What does class 3 allergy mean

Acute response

In the early stages of allergy, a type I hypersensitivity reaction against an allergen encountered for the first time and presented by a professional antigen-presenting cell causes a response in a type of immune cell called a TH2 lymphocyte; a subset of T cells that produce a cytokine called interleukin-4 (IL-4). These TH2 cells interact with other lymphocytes called B cells, whose role is production of antibodies. Coupled with signals provided by IL-4, this interaction stimulates the B cell to start production of a large quantity of a specific type of antibody known as IgE. Secreted IgE circulates in the blood and binds to an IgE-specific receptor (a helpful of Fc receptor called FcεRI) on the surface of other kinds of immune cells called mast cells and basophils, which are both involved in the acute inflammatory response.

The IgE-coated cells, at this stage, are sensitized to the allergen.[32]

If later exposure to the same allergen occurs, the allergen can bind to the IgE molecules held on the surface of the mast cells or basophils. Cross-linking of the IgE and Fc receptors occurs when more than one IgE-receptor complicated interacts with the same allergenic molecule, and activates the sensitized cell. Activated mast cells and basophils undergo a process called degranulation, during which they release histamine and other inflammatory chemical mediators (cytokines, interleukins, leukotrienes, and prostaglandins) from their granules into the surrounding tissue causing several systemic effects, such as vasodilation, mucous secretion, nerve stimulation, and smooth muscle contraction.

This results in rhinorrhea, itchiness, dyspnea, and anaphylaxis. Depending on the individual, allergen, and mode of introduction, the symptoms can be system-wide (classical anaphylaxis), or localized to specific body systems; asthma is localized to the respiratory system and eczema is localized to the dermis.[32]

Late-phase response

After the chemical mediators of the acute response subside, late-phase responses can often happen. This is due to the migration of other leukocytes such as neutrophils, lymphocytes, eosinophils and macrophages to the initial site. The reaction is generally seen 2–24 hours after the original reaction.[73] Cytokines from mast cells may frolic a role in the persistence of long-term effects.

Late-phase responses seen in asthma are slightly diverse from those seen in other allergic responses, although they are still caused by release of mediators from eosinophils and are still dependent on activity of TH2 cells.[74]

Allergic contact dermatitis

Although allergic contact dermatitis is termed an «allergic» reaction (which generally refers to type I hypersensitivity), its pathophysiology actually involves a reaction that more correctly corresponds to a type IV hypersensitivity reaction.[75] In type IV hypersensitivity, there is activation of certain types of T cells (CD8+) that destroy target cells on contact, as well as activated macrophages that produce hydrolyticenzymes.


Diagnosis

Effective management of allergic diseases relies on the ability to make an precise diagnosis.[76] Allergy testing can assist confirm or law out allergies.[77][78] Correct diagnosis, counseling, and avoidance advice based on valid allergy test results reduces the incidence of symptoms and need for medications, and improves quality of life.[77] To assess the presence of allergen-specific IgE antibodies, two diverse methods can be used: a skin prick test, or an allergy blood test.

Both methods are recommended, and they own similar diagnostic value.[78][79]

Skin prick tests and blood tests are equally cost-effective, and health economic evidence shows that both tests were cost-effective compared with no test.[77] Also, early and more precise diagnoses save cost due to reduced consultations, referrals to secondary care, misdiagnosis, and emergency admissions.[80]

Allergy undergoes dynamic changes over time.

Regular allergy testing of relevant allergens provides information on if and how patient management can be changed, in order to improve health and quality of life.

What does class 3 allergy mean

Annual testing is often the practice for determining whether allergy to milk, egg, soy, and wheat own been outgrown, and the testing interval is extended to 2–3 years for allergy to peanut, tree nuts, fish, and crustacean shellfish.[78] Results of follow-up testing can guide decision-making regarding whether and when it is safe to introduce or re-introduce allergenic food into the diet.[81]

Patch testing

Main article: Patch test

Patch testing is a method used to determine if a specific substance causes allergic inflammation of the skin.

It tests for delayed reactions. It is used to assist ascertain the cause of skin contact allergy, or contact dermatitis. Adhesive patches, generally treated with a number of common allergic chemicals or skin sensitizers, are applied to the back. The skin is then examined for possible local reactions at least twice, generally at 48 hours after application of the patch, and again two or three days later.

Other testing

Challenge testing: Challenge testing is when little amounts of a suspected allergen are introduced to the body orally, through inhalation, or via other routes.

Except for testing food and medication allergies, challenges are rarely performed. When this type of testing is chosen, it must be closely supervised by an allergist.

Elimination/challenge tests: This testing method is used most often with foods or medicines. A patient with a suspected allergen is instructed to modify his diet to totally avoid that allergen for a set time. If the patient experiences significant improvement, he may then be «challenged» by reintroducing the allergen, to see if symptoms are reproduced.

Unreliable tests: There are other types of allergy testing methods that are unreliable, including applied kinesiology (allergy testing through muscle relaxation), cytotoxicity testing, urine autoinjection, skin titration (Rinkel method), and provocative and neutralization (subcutaneous) testing or sublingual provocation.[89]

Blood testing

An allergy blood test is quick and simple, and can be ordered by a licensed health care provider (e.g., an allergy specialist) or general practitioner.

Unlike skin-prick testing, a blood test can be performed irrespective of age, skin condition, medication, symptom, disease activity, and pregnancy. Adults and children of any age can get an allergy blood test. For babies and extremely young children, a single needle stick for allergy blood testing is often more tender than several skin pricks.

An allergy blood test is available through most laboratories. A sample of the patient’s blood is sent to a laboratory for analysis, and the results are sent back a few days later. Multiple allergens can be detected with a single blood sample. Allergy blood tests are extremely safe, since the person is not exposed to any allergens during the testing procedure.

The test measures the concentration of specific IgE antibodies in the blood. Quantitative IgE test results increase the possibility of ranking how diverse substances may affect symptoms. A law of thumb is that the higher the IgE antibody worth, the greater the likelihood of symptoms. Allergens found at low levels that today do not result in symptoms can not assist predict future symptom development. The quantitative allergy blood result can assist determine what a patient is allergic to, assist predict and follow the disease development, estimate the risk of a severe reaction, and explain cross-reactivity.[84][85]

A low entire IgE level is not adequate to law out sensitization to commonly inhaled allergens.[86]Statistical methods, such as ROC curves, predictive worth calculations, and likelihood ratios own been used to examine the relationship of various testing methods to each other.

These methods own shown that patients with a high entire IgE own a high probability of allergic sensitization, but further investigation with allergy tests for specific IgE antibodies for a carefully chosen of allergens is often warranted.

Laboratory methods to measure specific IgE antibodies for allergy testing include enzyme-linked immunosorbent assay (ELISA, or EIA),[87]radioallergosorbent test (RAST)[87] and fluorescent enzyme immunoassay (FEIA).[88]

Skin prick testing

Skin testing is also known as «puncture testing» and «prick testing» due to the series of tiny punctures or pricks made into the patient’s skin.

Little amounts of suspected allergens and/or their extracts (e.g., pollen, grass, mite proteins, peanut extract) are introduced to sites on the skin marked with pen or dye (the ink/dye should be carefully selected, lest it cause an allergic response itself). A little plastic or metal device is used to puncture or prick the skin. Sometimes, the allergens are injected «intradermally» into the patient’s skin, with a needle and syringe. Common areas for testing include the inside forearm and the back.

If the patient is allergic to the substance, then a visible inflammatory reaction will generally happen within 30minutes.

This response will range from slight reddening of the skin to a full-blown hive (called «wheal and flare») in more sensitive patients similar to a mosquito bite. Interpretation of the results of the skin prick test is normally done by allergists on a scale of severity, with +/− meaning borderline reactivity, and 4+ being a large reaction. Increasingly, allergists are measuring and recording the diameter of the wheal and flare reaction. Interpretation by well-trained allergists is often guided by relevant literature.[82] Some patients may believe they own sure their own allergic sensitivity from observation, but a skin test has been shown to be much better than patient observation to detect allergy.[83]

If a serious life-threatening anaphylactic reaction has brought a patient in for evaluation, some allergists will prefer an initial blood test prior to performing the skin prick test.

Skin tests may not be an option if the patient has widespread skin disease, or has taken antihistamines in the final several days.

Differential diagnosis

Before a diagnosis of allergic disease can be confirmed, other possible causes of the presenting symptoms should be considered.[90]Vasomotor rhinitis, for example, is one of numerous illnesses that share symptoms with allergic rhinitis, underscoring the need for professional differential diagnosis.[91] Once a diagnosis of asthma, rhinitis, anaphylaxis, or other allergic disease has been made, there are several methods for discovering the causative agent of that allergy.


Prevention

Further information: Allergy prevention in children

Giving peanut products early may decrease the risk allergies while only breastfeeding during at least the first few months of life may decrease the risk of dermatitis.[92][93] There is no excellent evidence that a mother’s diet during pregnancy or breastfeeding affects the risk.[92] Nor is there evidence that delayed introduction of certain foods is useful.[92] Early exposure to potential allergens may actually be protective.[6]

Fish oil supplementation during pregnancy is associated with a lower risk.[93] Probiotic supplements during pregnancy or infancy may assist to prevent atopic dermatitis.[94][95]



What You Need to Know About Food Allergy Testing

by David Stukus, MD

Whenever I meet with families for the first time and enquire the parents whether their kid has any food allergies, I often hear the following reply: “I don’t know, he/she’s never been tested”.

This always presents a amazing chance to discuss the role of diagnostic testing for food allergies, as I’d love to do in this forum.

Before we go any further, I’d love to define some common terms that you may encounter when reading about or discussing food allergies:

  • IgE mediated hypersensitivity/allergy – Commonly referred to as “food allergy”, in which IgE antibody specific for a food is formed and attaches to the allergy cells throughout the body. Whenever that food is ingested, it causes immediate onset symptoms, generally within minutes or up to 3 hours after ingestion.

    Typical symptoms include hives, swelling, itchy/water nose and eyes, difficulty breathing/swallowing, vomiting, and can progress to loss of consciousness. Skin prick or blood specific IgE testing is extremely likely to be positive for that food.

  • Anaphylaxis – Rapid onset, progressive, severe symptoms involving more than one organ system that can happen with IgE mediated food allergy.
  • Sensitization – This is the detection of specific immunoglobulin E (IgE) through skin prick or blood testing towards a specific food, but without the development of symptoms after that food is ingested. In other words, a positive allergy test result to a food that your kid has eaten without any problems, or has never eaten.
  • Allergy – This is an immune response to a specific food.

    Symptoms should happen every time that food is ingested. These immune system changes drop into two categories: Immunoglobulin E (IgE) mediated and non-IgE-mediated.

  • Non-IgE mediated reaction – This is an immunologically mediated, typically delayed-onset reaction to a specific food. This is mediated by other parts of the immune system separate from IgE, specifically T-cells. These symptoms are not immediate in onset and can happen hours to days after ingestion. Anaphylaxis is not part of this response and most symptoms involve the gastrointestinal tract, with vomiting, upset stomach, diarrhea, or blood in the stool. Skin prick or blood specific IgE testing is negative.
  • Sensitivity or intolerance – This is a non-immunologic response to a certain food or foods.

    Symptoms happen when that food is consumed, but may be variable over time. This also most often includes gastrointestinal symptoms and does not include symptoms observed with IgE mediated reactions. Skin prick or blood specific IgE testing is negative.

When trying to determine whether a kid has a food allergy, there are numerous steps involved. First, the most significant part is taking a careful history of suspected foods, the timing and types of symptoms that happen, and any treatment that has before used to assist make symptoms better.

What does class 3 allergy mean

If the history is consistent with an IgE mediated allergy, then testing is often pursued. However, a excellent law of thumb to remember is, if your kid can eat a food without developing any symptoms, then they are unlikely to be allergic to that food. Why is that? Because the best test is actual ingestion of the food. In regards to IgE mediated allergy, you’re almost always going to know if a certain food makes your kid ill, and there are no ‘hidden’ food allergies. In numerous circumstances, the history is more consistent with non-IgE mediated symptoms or intolerance and skin prick or specific IgE testing is not helpful, necessary, or indicated.

This is the point when numerous families enquire, “Why don’t we just do the allergy tests to discover out for sure?” If only it were so easy.

Before we discuss any further, I’d love to mention something that is extremely significant to hold in mind when discussing food allergy testing. A positive test result for food allergy is not, in and of itself, diagnostic for food allergy. These tests are best utilized to assist confirm a suspicious history for IgE mediated food allergies.

They own high rates of falsely elevated and meaningless results and are not useful screening tools. Some commercial laboratories offer convenient “screening panels”, in which numerous diverse foods are included. These are rarely utilized by Allergists/Immunologists, but more commonly ordered by primary care providers. This often results in falsely elevated results, along with diagnostic confusion and unnecessary dietary elimination. Ultimately, your kid may own food(s) removed from their diet for no reason other than a meaningless positive test result.

This may then lead to anxiety, family hardship due to food avoidance, and potentially nutritional deficiencies.

There are 3 main ways to test for IgE mediated food allergy:

When trying to determine whether a kid has a food allergy, there are numerous steps involved. First, the most significant part is taking a careful history of suspected foods, the timing and types of symptoms that happen, and any treatment that has before used to assist make symptoms better.

What does class 3 allergy mean

If the history is consistent with an IgE mediated allergy, then testing is often pursued. However, a excellent law of thumb to remember is, if your kid can eat a food without developing any symptoms, then they are unlikely to be allergic to that food. Why is that? Because the best test is actual ingestion of the food. In regards to IgE mediated allergy, you’re almost always going to know if a certain food makes your kid ill, and there are no ‘hidden’ food allergies. In numerous circumstances, the history is more consistent with non-IgE mediated symptoms or intolerance and skin prick or specific IgE testing is not helpful, necessary, or indicated.

This is the point when numerous families enquire, “Why don’t we just do the allergy tests to discover out for sure?” If only it were so easy.

Before we discuss any further, I’d love to mention something that is extremely significant to hold in mind when discussing food allergy testing. A positive test result for food allergy is not, in and of itself, diagnostic for food allergy. These tests are best utilized to assist confirm a suspicious history for IgE mediated food allergies.

They own high rates of falsely elevated and meaningless results and are not useful screening tools. Some commercial laboratories offer convenient “screening panels”, in which numerous diverse foods are included. These are rarely utilized by Allergists/Immunologists, but more commonly ordered by primary care providers. This often results in falsely elevated results, along with diagnostic confusion and unnecessary dietary elimination. Ultimately, your kid may own food(s) removed from their diet for no reason other than a meaningless positive test result.

This may then lead to anxiety, family hardship due to food avoidance, and potentially nutritional deficiencies.

There are 3 main ways to test for IgE mediated food allergy:

    • Skin Prick Testing (SPT): This involves placing a drop of allergen onto the surface of the skin, and then pricking through it to introduce the allergen into the top layer of the skin. If specific IgE antibody towards that allergen is present and attached to the allergy cells, then an itchy bump and surrounding redness (wheal/flare) should develop within 15 minutes. These tests own a high negative predictive worth (when a test yields a negative result, it is extremely likely to be correct), but a low positive predictive worth (when a test yields a positive result, it is less likely to be correct) which can result in untrue positive test results.

      Thus, it is not a excellent screening tool but is a extremely dependable test to confirm a history that is consistent with an IgE mediated food allergy.
      In order to get precise results, every antihistamines should be discontinued for days before testing. A common myth is that skin prick testing is not dependable in young infants and children. Actually, skin prick testing to foods is dependable at any age if you own a history of IgE mediated food allergy. Tests may be negative in young children when they are performed for other conditions such as non-IgE mediated formula or food intolerance.

  • Cardiovascular (eg, tachycardia, hypotension)
  • Generalized (eg, anaphylactic shock).

    By definition, anaphylaxis is a life-threatening reaction that occurs on exposure to an allergen and involves acute respiratory distress, cardiovascular failure, or involvement of two or more organ systems.4

  • Cutaneous (eg, acute urticaria, angioedema)
  • Specific IgE (sIgE) Blood Testing (previously and commonly referred to as RAST or ImmunoCAP testing): This test measures levels of specific IgE directed towards foods in the blood. The range, depending upon the laboratory techniques, can go from kU/L to kU/L. This also has a extremely high negative predictive worth but a low positive predictive worth.

    Mildly elevated results are often encountered, especially in children who own other types of allergic conditions such as eczema, asthma, and allergic rhinitis. The predictive values for likelihood of an allergy being present differ with every food, but in general, the higher the level, the more likely that an IgE mediated allergy is present. This is also a extremely poor screening test due to the high rates of falsely elevated and meaningless results.

    I’ve met numerous families whose children own been ‘screened for food allergies’ in the setting of eczema or other conditions and the report lists every food that was tested as being ‘high’, as their cutoff for reporting this is often set extremely low, at levels that are generally meaningless.

    This leads to diagnostic confusion and unnecessary dietary elimination. In addition, numerous laboratories will report an arbitrary class designation (a created worth that is assigned to a result that has no meaning or scientific basis), along with the actual level of specific IgE obtained. This is of no clinical use and also does not assist determine whether food allergy is present. It is also commonly misunderstood that higher blood test levels indicate increased ”severity”. Unfortunately there is no test that can determine severity. Individuals with higher blood (or skin) tests are at no more increased risk of anaphylaxis than someone with minimally positive tests.

    TAKE NOTE: «Class Levels» are meaningless.

  • Respiratory (eg, acute bronchospasm, rhinoconjunctivitis)
  • Gastrointestinal (eg, vomiting, diarrhea)
  • Physician Supervised Oral Food Challenge (commonly referred to as IOFC on KFA):This entails consumption of gradually increasing amounts of the suspected food allergen while being supervised by a physician, generally an Allergist.

    If no symptoms develop that are consistent with an IgE mediated food allergy (hives, swelling, anaphylaxis), then it makes the presence of IgE directed toward that food unlikely. This is often considered the gold standard for food allergy testing, and can be considered a excellent way to ‘rule out’ food allergy or determine if a previously diagnosed food allergy has gone away. This is time consuming as most challenges take hours to finish but can be a extremely dependable test.

    TAKE NOTE: The gold standard for diagnosing a food allergy is through a physician-supervised oral food challenge.

  • Immulite (Siemens AG, Berlin, Germany)
  • ImmunoCAP (Phadia AB, Uppsala, Sweden)
  • HYTEC (Hycor/Agilent, Garden Grove, CA).

As you can see, performing diagnostic testing for food allergies can be extremely complicated and requires careful consideration about what tests to order and how to interpret them.

There are extremely few indications to act out an extensive ‘screening panel’ for food allergies. However, obtaining a careful history of what specific foods cause symptoms and then using the type of symptoms can be a helpful guide to determine whether specific IgE testing is worth pursuing, or to go in a diverse direction.

Lastly, a expression of caution regarding other commonly used techniques (often utilized by non-board certified Allergists/Immunologists) that you may encounter. Specific IgG blood testing for foods, muscle provocation testing, acupuncture, hair/urine analysis, and applied kinesiology are not validated, standardized, or FDA approved tests for the diagnosis of food allergy or food intolerance.

Use of these tests is not recommended by the American Academy of Asthma, Allergy, and Immunology, or supported by the Guidelines for the Diagnosis and Management of Food Allergy, published in (Journal of Allergy and Clinical Immunology, (6); supplement S).

References

Guidelines for the Diagnosis and Management of Food Allergy, published in (Journal of Allergy and Clinical Immunology, (6); supplement S).

Dr. David Stukus is an Assistant Professor of Pediatrics in the Section of Allergy/Immunology at Nationwide Children’s Hospital in Columbus, Ohio. In addition to his interest in caring for families with food allergies and other allergic conditions, he also serves as the Director of the Complicated Asthma Clinic.

He currently serves as the chair of the Medical Advisory Team for Kids With Food Allergies and sits on the Board of Directors for the Asthma and Allergy Foundation of America. He previously completed his residency at Nationwide Children’s Hospital and his fellowship at the Cleveland Clinic. You can follow him on @AllergyKidsDoc.

Medical review October and April

Health care providers often need to assess allergic disorders such as allergic rhinoconjunctivitis, asthma, and allergies to foods, drugs, latex, and venom, both in the hospital and in the clinic.

Unfortunately, some symptoms, such as chronic nasal symptoms, can happen in both allergic and nonallergic disorders, and this overlap can confound the diagnosis and therapy.

What does class 3 allergy mean

Studies propose that when clinicians use the history and physical examination alone in evaluating possible allergic disease, the accuracy of their diagnoses rarely exceeds 50%.1

Blood tests are now available that measure immunoglobulin E (IgE) directed against specific antigens. These in vitro tests can be significant tools in assessing a patient whose history suggests an allergic disease.2 However, neither allergy skin testing nor these blood tests are intended to be used for screening: they may be most useful as confirmatory diagnostic tests in cases in which the pretest clinical impression of allergic disease is high.

In susceptible people, IgE is produced by B cells in response to specific antigens such as foods, pollens, latex, and drugs.

This antigen-specific (or allergen-specific) IgE circulates in the serum and binds to high-affinity IgE receptors on immune effector cells such as mast cells located throughout the body.

Upon subsequent exposure to the same allergen, IgE receptors cross-link and initiate downstream signaling events that trigger mast cell degranulation and an immediate allergic response—hence the term immediate (or Gell-Coombs type I) hypersensitivity.3

Common manifestations of type I hypersensitivity reactions include signs and symptoms that can be:

  1. Respiratory (eg, acute bronchospasm, rhinoconjunctivitis)
  2. Gastrointestinal (eg, vomiting, diarrhea)
  3. Cardiovascular (eg, tachycardia, hypotension)
  4. Cutaneous (eg, acute urticaria, angioedema)
  5. Generalized (eg, anaphylactic shock).

    By definition, anaphylaxis is a life-threatening reaction that occurs on exposure to an allergen and involves acute respiratory distress, cardiovascular failure, or involvement of two or more organ systems.4

The blood tests for allergic disease are immunoassays that measure the level of IgE specific to a specific allergen.

What does class 3 allergy mean

The tests can be used to assess sensitivity to various allergens, for example, to common inhalants such as dust mites and pollens and to foods, drugs, venom, and latex.

Types of immunoassays include enzyme-linked immunosorbent assays (ELISAs), fluorescent enzyme immunoassays (FEIAs), and radioallergosorbent assays (RASTs). At present, most commercial laboratories use one of three autoanalyzer systems to measure specific IgE:

  1. ImmunoCAP (Phadia AB, Uppsala, Sweden)
  2. Immulite (Siemens AG, Berlin, Germany)
  3. HYTEC (Hycor/Agilent, Garden Grove, CA).

These systems use a solid-phase polymer (cellulose or avidin) in which the antigen is embedded.

The polymer also facilitates binding of IgE and, therefore, increases the sensitivity of the test.5 Specific IgE from the patient’s serum binds to the allergen embedded in the polymer, and then unbound antibodies are washed off.

Despite the term “RAST,” these systems do not use radiation. A fluorescent antibody is added that binds to the patient’s IgE, and the quantity of IgE present is calculated from the quantity of fluorescence.6 Results are reported in kilounits of antibody per liter (kU/L) or nanograms per milliliter (ng/mL).5–7

In general, the sensitivity of these tests ranges from 60% to 95% and their specificity from 30% to 95%, with a concordance among diverse immunoassays of 75% to 90%.8

Levels of IgE for a specific allergen are also divided into semiquantitative classes, from class I to class V or VI.

In general, class I and class II correlate with a low level of allergen sensitization and, often, with a low likelihood of a clinical reaction. On the other hand, classes V and VI reflect higher degrees of sensitization and generally correlate with IgE-mediated clinical reactions upon allergen exposure.

The interpretation of a positive (ie, “nonzero”) test result must be individualized on the basis of clinical presentation and risk factors. A specialist can make an significant contribution by helping to interpret any positive test result or a negative test result that does not correlate with the patient’s history.

Allergy blood testing is convenient, since it involves only a standard blood draw.

In theory, allergy blood testing may be safer, since it does not expose the patient to any allergens.

On the other hand, numerous patients experience bruising from venipuncture performed for any reason: 16% in one survey.9 In another survey,10 adverse reactions of any type occurred in % of patients undergoing venipuncture but only in % of those undergoing allergy skin testing. Therefore, allergy blood testing may be most appropriate in situations in which a patient’s history suggests that he or she may be at risk of a systemic reaction from a traditional skin test or in cases in which skin testing is not possible (eg, extensive eczema).

Another advantage of allergy blood testing is that it is not affected by drugs such as antihistamines or tricyclic antidepressants that suppress the histamine response, which is a problem with skin testing.

Allergy blood testing may also be useful in patients on long-term glucocorticoid therapy, although the data conflict.

Prolonged oral glucocorticoid use is associated with a decrease in mast cell density and histamine content in the skin,11,12 although in one study a corticosteroid was found not to affect the results of skin-prick testing for allergy.13 Thus, allergy blood testing can be performed in patients who own severe eczema or dermatographism or who cannot safely suspend taking antihistamines or tricyclic antidepressants.

Immune system response to a substance that most people tolerate well

For the medical journal of this title, see Allergy (journal).

Allergy
Hives are a common allergic symptom
Specialty Immunology
Symptoms Red eyes, itchy rash, runny nose, shortness of breath, swelling, sneezing[1]
Types Hay fever, food allergies, atopic dermatitis, allergic asthma, anaphylaxis[2]
Causes Genetic and environmental factors[3]
Diagnostic method Based on symptoms, skin prick test, blood test[4]
Differential diagnosis Food intolerances, food poisoning[5]
Prevention Early exposure to potential allergens[6]
Treatment Avoiding known allergens, medications, allergen immunotherapy[7]
Medication Steroids, antihistamines, epinephrine, mast cell stabilizers, antileukotrienes[7][8][9][10]
Frequency Common[11]

Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment.[12] These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis.[2] Symptoms may include red eyes, an itchy rash, sneezing, a runny nose, shortness of breath, or swelling.[1]Food intolerances and food poisoning are separate conditions.[4][5]

Common allergens include pollen and certain foods.[12] Metals and other substances may also cause problems.[12] Food, insect stings, and medications are common causes of severe reactions.[3] Their development is due to both genetic and environmental factors.[3] The underlying mechanism involves immunoglobulin E antibodies (IgE), part of the body’s immune system, binding to an allergen and then to a receptor on mast cells or basophils where it triggers the release of inflammatory chemicals such as histamine.[13] Diagnosis is typically based on a person’s medical history.[4] Further testing of the skin or blood may be useful in certain cases.[4] Positive tests, however, may not mean there is a significant allergy to the substance in question.[14]

Early exposure to potential allergens may be protective.[6] Treatments for allergies include avoiding known allergens and the use of medications such as steroids and antihistamines.[7] In severe reactions injectable adrenaline (epinephrine) is recommended.[8]Allergen immunotherapy, which gradually exposes people to larger and larger amounts of allergen, is useful for some types of allergies such as hay fever and reactions to insect bites.[7] Its use in food allergies is unclear.[7]

Allergies are common.[11] In the developed world, about 20% of people are affected by allergic rhinitis,[15] about 6% of people own at least one food allergy,[4][6] and about 20% own atopic dermatitis at some point in time.[16] Depending on the country about 1–18% of people own asthma.[17][18] Anaphylaxis occurs in between –2% of people.[19] Rates of numerous allergic diseases appear to be increasing.[8][20] The expression «allergy» was first used by Clemens von Pirquet in [3]

As you can see, performing diagnostic testing for food allergies can be extremely complicated and requires careful consideration about what tests to order and how to interpret them.

There are extremely few indications to act out an extensive ‘screening panel’ for food allergies. However, obtaining a careful history of what specific foods cause symptoms and then using the type of symptoms can be a helpful guide to determine whether specific IgE testing is worth pursuing, or to go in a diverse direction.

Lastly, a expression of caution regarding other commonly used techniques (often utilized by non-board certified Allergists/Immunologists) that you may encounter.

Specific IgG blood testing for foods, muscle provocation testing, acupuncture, hair/urine analysis, and applied kinesiology are not validated, standardized, or FDA approved tests for the diagnosis of food allergy or food intolerance. Use of these tests is not recommended by the American Academy of Asthma, Allergy, and Immunology, or supported by the Guidelines for the Diagnosis and Management of Food Allergy, published in (Journal of Allergy and Clinical Immunology, (6); supplement S).

References

Guidelines for the Diagnosis and Management of Food Allergy, published in (Journal of Allergy and Clinical Immunology, (6); supplement S).

Dr.

David Stukus is an Assistant Professor of Pediatrics in the Section of Allergy/Immunology at Nationwide Children’s Hospital in Columbus, Ohio. In addition to his interest in caring for families with food allergies and other allergic conditions, he also serves as the Director of the Complicated Asthma Clinic. He currently serves as the chair of the Medical Advisory Team for Kids With Food Allergies and sits on the Board of Directors for the Asthma and Allergy Foundation of America.

What does class 3 allergy mean

He previously completed his residency at Nationwide Children’s Hospital and his fellowship at the Cleveland Clinic. You can follow him on @AllergyKidsDoc.

Medical review October and April

Health care providers often need to assess allergic disorders such as allergic rhinoconjunctivitis, asthma, and allergies to foods, drugs, latex, and venom, both in the hospital and in the clinic.

Unfortunately, some symptoms, such as chronic nasal symptoms, can happen in both allergic and nonallergic disorders, and this overlap can confound the diagnosis and therapy. Studies propose that when clinicians use the history and physical examination alone in evaluating possible allergic disease, the accuracy of their diagnoses rarely exceeds 50%.1

Blood tests are now available that measure immunoglobulin E (IgE) directed against specific antigens.

These in vitro tests can be significant tools in assessing a patient whose history suggests an allergic disease.2 However, neither allergy skin testing nor these blood tests are intended to be used for screening: they may be most useful as confirmatory diagnostic tests in cases in which the pretest clinical impression of allergic disease is high.

In susceptible people, IgE is produced by B cells in response to specific antigens such as foods, pollens, latex, and drugs.

This antigen-specific (or allergen-specific) IgE circulates in the serum and binds to high-affinity IgE receptors on immune effector cells such as mast cells located throughout the body.

Upon subsequent exposure to the same allergen, IgE receptors cross-link and initiate downstream signaling events that trigger mast cell degranulation and an immediate allergic response—hence the term immediate (or Gell-Coombs type I) hypersensitivity.3

Common manifestations of type I hypersensitivity reactions include signs and symptoms that can be:

  1. Respiratory (eg, acute bronchospasm, rhinoconjunctivitis)
  2. Gastrointestinal (eg, vomiting, diarrhea)
  3. Cardiovascular (eg, tachycardia, hypotension)
  4. Cutaneous (eg, acute urticaria, angioedema)
  5. Generalized (eg, anaphylactic shock).

    By definition, anaphylaxis is a life-threatening reaction that occurs on exposure to an allergen and involves acute respiratory distress, cardiovascular failure, or involvement of two or more organ systems.4

The blood tests for allergic disease are immunoassays that measure the level of IgE specific to a specific allergen. The tests can be used to assess sensitivity to various allergens, for example, to common inhalants such as dust mites and pollens and to foods, drugs, venom, and latex.

Types of immunoassays include enzyme-linked immunosorbent assays (ELISAs), fluorescent enzyme immunoassays (FEIAs), and radioallergosorbent assays (RASTs).

At present, most commercial laboratories use one of three autoanalyzer systems to measure specific IgE:

  1. ImmunoCAP (Phadia AB, Uppsala, Sweden)
  2. Immulite (Siemens AG, Berlin, Germany)
  3. HYTEC (Hycor/Agilent, Garden Grove, CA).

These systems use a solid-phase polymer (cellulose or avidin) in which the antigen is embedded. The polymer also facilitates binding of IgE and, therefore, increases the sensitivity of the test.5 Specific IgE from the patient’s serum binds to the allergen embedded in the polymer, and then unbound antibodies are washed off.

Despite the term “RAST,” these systems do not use radiation.

A fluorescent antibody is added that binds to the patient’s IgE, and the quantity of IgE present is calculated from the quantity of fluorescence.6 Results are reported in kilounits of antibody per liter (kU/L) or nanograms per milliliter (ng/mL).5–7

In general, the sensitivity of these tests ranges from 60% to 95% and their specificity from 30% to 95%, with a concordance among diverse immunoassays of 75% to 90%.8

Levels of IgE for a specific allergen are also divided into semiquantitative classes, from class I to class V or VI.

In general, class I and class II correlate with a low level of allergen sensitization and, often, with a low likelihood of a clinical reaction. On the other hand, classes V and VI reflect higher degrees of sensitization and generally correlate with IgE-mediated clinical reactions upon allergen exposure.

The interpretation of a positive (ie, “nonzero”) test result must be individualized on the basis of clinical presentation and risk factors. A specialist can make an significant contribution by helping to interpret any positive test result or a negative test result that does not correlate with the patient’s history.

Allergy blood testing is convenient, since it involves only a standard blood draw.

In theory, allergy blood testing may be safer, since it does not expose the patient to any allergens.

On the other hand, numerous patients experience bruising from venipuncture performed for any reason: 16% in one survey.9 In another survey,10 adverse reactions of any type occurred in % of patients undergoing venipuncture but only in % of those undergoing allergy skin testing. Therefore, allergy blood testing may be most appropriate in situations in which a patient’s history suggests that he or she may be at risk of a systemic reaction from a traditional skin test or in cases in which skin testing is not possible (eg, extensive eczema).

Another advantage of allergy blood testing is that it is not affected by drugs such as antihistamines or tricyclic antidepressants that suppress the histamine response, which is a problem with skin testing.

Allergy blood testing may also be useful in patients on long-term glucocorticoid therapy, although the data conflict.

Prolonged oral glucocorticoid use is associated with a decrease in mast cell density and histamine content in the skin,11,12 although in one study a corticosteroid was found not to affect the results of skin-prick testing for allergy.13 Thus, allergy blood testing can be performed in patients who own severe eczema or dermatographism or who cannot safely suspend taking antihistamines or tricyclic antidepressants.

Immune system response to a substance that most people tolerate well

For the medical journal of this title, see Allergy (journal).

Allergy
Hives are a common allergic symptom
Specialty Immunology
Symptoms Red eyes, itchy rash, runny nose, shortness of breath, swelling, sneezing[1]
Types Hay fever, food allergies, atopic dermatitis, allergic asthma, anaphylaxis[2]
Causes Genetic and environmental factors[3]
Diagnostic method Based on symptoms, skin prick test, blood test[4]
Differential diagnosis Food intolerances, food poisoning[5]
Prevention Early exposure to potential allergens[6]
Treatment Avoiding known allergens, medications, allergen immunotherapy[7]
Medication Steroids, antihistamines, epinephrine, mast cell stabilizers, antileukotrienes[7][8][9][10]
Frequency Common[11]

Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment.[12] These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis.[2] Symptoms may include red eyes, an itchy rash, sneezing, a runny nose, shortness of breath, or swelling.[1]Food intolerances and food poisoning are separate conditions.[4][5]

Common allergens include pollen and certain foods.[12] Metals and other substances may also cause problems.[12] Food, insect stings, and medications are common causes of severe reactions.[3] Their development is due to both genetic and environmental factors.[3] The underlying mechanism involves immunoglobulin E antibodies (IgE), part of the body’s immune system, binding to an allergen and then to a receptor on mast cells or basophils where it triggers the release of inflammatory chemicals such as histamine.[13] Diagnosis is typically based on a person’s medical history.[4] Further testing of the skin or blood may be useful in certain cases.[4] Positive tests, however, may not mean there is a significant allergy to the substance in question.[14]

Early exposure to potential allergens may be protective.[6] Treatments for allergies include avoiding known allergens and the use of medications such as steroids and antihistamines.[7] In severe reactions injectable adrenaline (epinephrine) is recommended.[8]Allergen immunotherapy, which gradually exposes people to larger and larger amounts of allergen, is useful for some types of allergies such as hay fever and reactions to insect bites.[7] Its use in food allergies is unclear.[7]

Allergies are common.[11] In the developed world, about 20% of people are affected by allergic rhinitis,[15] about 6% of people own at least one food allergy,[4][6] and about 20% own atopic dermatitis at some point in time.[16] Depending on the country about 1–18% of people own asthma.[17][18] Anaphylaxis occurs in between –2% of people.[19] Rates of numerous allergic diseases appear to be increasing.[8][20] The expression «allergy» was first used by Clemens von Pirquet in [3]


Cause

Risk factors for allergy can be placed in two general categories, namely host and environmental factors.[31] Host factors include heredity, sex, race, and age, with heredity being by far the most significant.

However, there own been recent increases in the incidence of allergic disorders that cannot be explained by genetic factors alone. Four major environmental candidates are alterations in exposure to infectious diseases during early childhood, environmental pollution, allergen levels, and dietary changes.[32]

Insect stings

Main article: Insect sting allergy

Typically, insects which generate allergic responses are either stinging insects (wasps, bees, hornets and ants) or biting insects (mosquitoes, ticks).

Stinging insects inject venom into their victims, whilst biting insects normally introduce anti-coagulants.

Genetics

Allergic diseases are strongly familial: identical twins are likely to own the same allergic diseases about 70% of the time; the same allergy occurs about 40% of the time in non-identical twins.[50] Allergic parents are more likely to own allergic children,[51] and those children’s allergies are likely to be more severe than those in children of non-allergic parents. Some allergies, however, are not consistent along genealogies; parents who are allergic to peanuts may own children who are allergic to ragweed. It seems that the likelihood of developing allergies is inherited and related to an irregularity in the immune system, but the specific allergen is not.[51]

The risk of allergic sensitization and the development of allergies varies with age, with young children most at risk.[52] Several studies own shown that IgE levels are highest in childhood and drop rapidly between the ages of 10 and 30 years.[52] The peak prevalence of hay fever is highest in children and young adults and the incidence of asthma is highest in children under [53]

Overall, boys own a higher risk of developing allergies than girls,[51] although for some diseases, namely asthma in young adults, females are more likely to be affected.[54] These differences between the sexes tend to decrease in adulthood.[51]

Ethnicity may frolic a role in some allergies; however, racial factors own been hard to separate from environmental influences and changes due to migration.[51] It has been suggested that diverse genetic loci are responsible for asthma, to be specific, in people of European, Hispanic, Asian, and African origins.[55]

Toxins interacting with proteins

Another non-food protein reaction, urushiol-induced contact dermatitis, originates after contact with poison ivy, eastern poison oak, western poison oak, or poison sumac.

Urushiol, which is not itself a protein, acts as a hapten and chemically reacts with, binds to, and changes the shape of integral membrane proteins on exposed skin cells. The immune system does not recognize the affected cells as normal parts of the body, causing a T-cell-mediated immune response.[46] Of these poisonous plants, sumac is the most virulent.[47] The resulting dermatological response to the reaction between urushiol and membrane proteins includes redness, swelling, papules, vesicles, blisters, and streaking.[48]

Estimates vary on the percentage of the population that will own an immune system response.

Approximately 25 percent of the population will own a strong allergic response to urushiol.

What does class 3 allergy mean

In general, approximately 80 percent to 90 percent of adults will develop a rash if they are exposed to milligrams (×10−5gr) of purified urushiol, but some people are so sensitive that it takes only a molecular trace on the skin to initiate an allergic reaction.[49]

Foods

Main article: Food allergy

A wide variety of foods can cause allergic reactions, but 90% of allergic responses to foods are caused by cow’s milk, soy, eggs, wheat, peanuts, tree nuts, fish, and shellfish.[33] Other food allergies, affecting less than 1 person per 10, population, may be considered «rare».[34] The use of hydrolysed milk baby formula versus standard milk baby formula does not appear to change the risk.[35]

The most common food allergy in the US population is a sensitivity to crustacea.[34] Although peanut allergies are notorious for their severity, peanut allergies are not the most common food allergy in adults or children.

Severe or life-threatening reactions may be triggered by other allergens, and are more common when combined with asthma.[33]

Rates of allergies differ between adults and children. Peanut allergies can sometimes be outgrown by children. Egg allergies affect one to two percent of children but are outgrown by about two-thirds of children by the age of 5.[36] The sensitivity is generally to proteins in the white, rather than the yolk.[37]

Milk-protein allergies are most common in children.[38] Approximately 60% of milk-protein reactions are immunoglobulin E-mediated, with the remaining generally attributable to inflammation of the colon.[39] Some people are unable to tolerate milk from goats or sheep as well as from cows, and numerous are also unable to tolerate dairy products such as cheese.

Roughly 10% of children with a milk allergy will own a reaction to beef. Beef contains little amounts of proteins that are present in greater abundance in cow’s milk.[40]Lactose intolerance, a common reaction to milk, is not a form of allergy at every, but rather due to the absence of an enzyme in the digestive tract.

Those with tree nut allergies may be allergic to one or to numerous tree nuts, including pecans, pistachios, pine nuts, and walnuts.[37] Also seeds, including sesame seeds and poppy seeds, contain oils in which protein is present, which may elicit an allergic reaction.[37]

Allergens can be transferred from one food to another through genetic engineering; however genetic modification can also remove allergens.

Little research has been done on the natural variation of allergen concentrations in unmodified crops.[41][42]

Medications

Main article: Drug allergy

See also: Adverse drug reaction and Drug eruption

About 10% of people report that they are allergic to penicillin; however, 90% turn out not to be.[45] Serious allergies only happen in about %.[45]

Hygiene hypothesis

Main article: Hygiene hypothesis

Allergic diseases are caused by inappropriate immunological responses to harmless antigens driven by a TH2-mediated immune response.

Numerous bacteria and viruses elicit a TH1-mediated immune response, which down-regulates TH2 responses. The first proposed mechanism of action of the hygiene hypothesis was that insufficient stimulation of the TH1 arm of the immune system leads to an overactive TH2 arm, which in turn leads to allergic disease.[56] In other words, individuals living in too sterile an environment are not exposed to enough pathogens to hold the immune system busy. Since our bodies evolved to deal with a certain level of such pathogens, when they are not exposed to this level, the immune system will attack harmless antigens and thus normally benign microbial objects—like pollen—will trigger an immune response.[57]

The hygiene hypothesis was developed to explain the observation that hay fever and eczema, both allergic diseases, were less common in children from larger families, which were, it is presumed, exposed to more infectious agents through their siblings, than in children from families with only one kid.

The hygiene hypothesis has been extensively investigated by immunologists and epidemiologists and has become an significant theoretical framework for the study of allergic disorders. It is used to explain the increase in allergic diseases that own been seen since industrialization, and the higher incidence of allergic diseases in more developed countries. The hygiene hypothesis has now expanded to include exposure to symbiotic bacteria and parasites as significant modulators of immune system development, along with infectious agents.

Epidemiological data support the hygiene hypothesis.

What does class 3 allergy mean

Studies own shown that various immunological and autoimmune diseases are much less common in the developing world than the industrialized world and that immigrants to the industrialized world from the developing world increasingly develop immunological disorders in relation to the length of time since arrival in the industrialized world.[58] Longitudinal studies in the third world protest an increase in immunological disorders as a country grows more affluent and, it is presumed, cleaner.[59] The use of antibiotics in the first year of life has been linked to asthma and other allergic diseases.[60] The use of antibacterial cleaning products has also been associated with higher incidence of asthma, as has birth by Caesarean section rather than vaginal birth.[61][62]

Latex

Latex can trigger an IgE-mediated cutaneous, respiratory, and systemic reaction.

The prevalence of latex allergy in the general population is believed to be less than one percent. In a hospital study, 1 in surgical patients ( percent) reported latex sensitivity, although the sensitivity among healthcare workers is higher, between seven and ten percent. Researchers attribute this higher level to the exposure of healthcare workers to areas with significant airborne latex allergens, such as operating rooms, intensive-care units, and dental suites.

These latex-rich environments may sensitize healthcare workers who regularly inhale allergenic proteins.[43]

The most prevalent response to latex is an allergic contact dermatitis, a delayed hypersensitive reaction appearing as dry, crusted lesions. This reaction generally lasts 48–96 hours. Sweating or rubbing the area under the glove aggravates the lesions, possibly leading to ulcerations.[43]Anaphylactic reactions happen most often in sensitive patients who own been exposed to a surgeon’s latex gloves during abdominal surgery, but other mucosal exposures, such as dental procedures, can also produce systemic reactions.[43]

Latex and banana sensitivity may cross-react.

Furthermore, those with latex allergy may also own sensitivities to avocado, kiwifruit, and chestnut.[44] These people often own perioral itching and local urticaria. Only occasionally own these food-induced allergies induced systemic responses. Researchers suspect that the cross-reactivity of latex with banana, avocado, kiwifruit, and chestnut occurs because latex proteins are structurally homologous with some other plant proteins.[43]

Stress

Chronic stress can aggravate allergic conditions.

This has been attributed to a T helper 2 (TH2)-predominant response driven by suppression of interleukin 12 by both the autonomic nervous system and the hypothalamic–pituitary–adrenal axis. Stress management in highly susceptible individuals may improve symptoms.[63]

Other environmental factors

There are differences between countries in the number of individuals within a population having allergies. Allergic diseases are more common in industrialized countries than in countries that are more traditional or agricultural, and there is a higher rate of allergic disease in urban populations versus rural populations, although these differences are becoming less defined.[64] Historically, the trees planted in urban areas were predominantly male to prevent litter from seeds and fruits, but the high ratio of male trees causes high pollen counts.[65]

Alterations in exposure to microorganisms is another plausible explanation, at present, for the increase in atopic allergy.[32] Endotoxin exposure reduces release of inflammatory cytokines such as TNF-α, IFNγ, interleukin, and interleukin from white blood cells (leukocytes) that circulate in the blood.[66] Certain microbe-sensing proteins, known as Toll-like receptors, found on the surface of cells in the body are also thought to be involved in these processes.[67]

Gutworms and similar parasites are present in untreated drinking water in developing countries, and were present in the water of developed countries until the routine chlorination and purification of drinking water supplies.[68] Recent research has shown that some common parasites, such as intestinal worms (e.g., hookworms), secrete chemicals into the gut wall (and, hence, the bloodstream) that suppress the immune system and prevent the body from attacking the parasite.[69] This gives rise to a new slant on the hygiene hypothesis theory—that co-evolution of humans and parasites has led to an immune system that functions correctly only in the presence of the parasites.

Without them, the immune system becomes unbalanced and oversensitive.[70] In specific, research suggests that allergies may coincide with the delayed establishment of gut flora in infants.[71] However, the research to support this theory is conflicting, with some studies performed in China and Ethiopia showing an increase in allergy in people infected with intestinal worms.[64] Clinical trials own been initiated to test the effectiveness of certain worms in treating some allergies.[72] It may be that the term ‘parasite’ could turn out to be inappropriate, and in fact a hitherto unsuspected symbiosis is at work.[72] For more information on this topic, see Helminthic therapy.


Signs and symptoms

Affected organ Common signs and symptoms
Nose Swelling of the nasal mucosa (allergic rhinitis) runny nose, sneezing
Sinuses Allergic sinusitis
Eyes Redness and itching of the conjunctiva (allergic conjunctivitis, watery)
Airways Sneezing, coughing, bronchoconstriction, wheezing and dyspnea, sometimes outright attacks of asthma, in severe cases the airway constricts due to swelling known as laryngeal edema
Ears Feeling of fullness, possibly pain, and impaired hearing due to the lack of eustachian tube drainage.

Skin Rashes, such as eczema and hives (urticaria)
Gastrointestinal tract Abdominal pain, bloating, vomiting, diarrhea

Many allergens such as dust or pollen are airborne particles. In these cases, symptoms arise in areas in contact with air, such as eyes, nose, and lungs. For instance, allergic rhinitis, also known as hay fever, causes irritation of the nose, sneezing, itching, and redness of the eyes.[21] Inhaled allergens can also lead to increased production of mucus in the lungs, shortness of breath, coughing, and wheezing.[22]

Aside from these ambient allergens, allergic reactions can result from foods, insect stings, and reactions to medications love aspirin and antibiotics such as penicillin.

Symptoms of food allergy include abdominal pain, bloating, vomiting, diarrhea, itchy skin, and swelling of the skin during hives. Food allergies rarely cause respiratory (asthmatic) reactions, or rhinitis.[23] Insect stings, food, antibiotics, and certain medicines may produce a systemic allergic response that is also called anaphylaxis; multiple organ systems can be affected, including the digestive system, the respiratory system, and the circulatory system.[24][25][26] Depending on the rate of severity, anaphylaxis can include skin reactions, bronchoconstriction, swelling, low blood pressure, coma, and death.

This type of reaction can be triggered suddenly, or the onset can be delayed. The nature of anaphylaxis is such that the reaction can seem to be subsiding, but may recur throughout a period of time.[26]

Skin

Substances that come into contact with the skin, such as latex, are also common causes of allergic reactions, known as contact dermatitis or eczema.[27] Skin allergies frequently cause rashes, or swelling and inflammation within the skin, in what is known as a «weal and flare» reaction characteristic of hives and angioedema.[28]

With insect stings a large local reaction may happen (an area of skin redness greater than 10cm in size).[29] It can final one to two days.[29] This reaction may also happen after immunotherapy.[30]


RELATED VIDEO: