What does class 4 peanut allergy mean

Class

IgE kU/L

Interpretation

0

<

Negative

0/1

Borderline / Equivocal

1

Equivocal

2

Positive

3

Positive

4

Strongly positive

5

Strongly positive

6

> or =

Strongly positive

Reference values apply to every ages.


Clinical ReferenceRecommendations for in-depth reading of a clinical nature

1.

Sicherer SH, Wood RA: Advances in diagnosing peanut allergy. J Allergy Clin ImmunolPract ;

2. Eller E, Bindslev-Jensen C: Clinical worth of component-resolved diagnostics in peanut-allergic patients. Allergy ;

3. Hong X, Caruso D, Kumar R, et al: IgE, but not IgG4, antibodies to Ara h 2 distinguish peanut allergy from asymptomatic peanut sensitization. Allergy ;

4. Klemans RJ, van Os-Medendorp H, Blankestijn M, et al: Diagnostic accuracy of specific IgE to components in diagnosing peanut allergy: a systematic review. Clin Exp Allergy ;

5.

Asarnoj A, Nilsson C, Lidholm J, et al: Peanut component Ara h 8 sensitization and tolerance to peanut. J Allergy Clin Immunol ;


InterpretationProvides information to help in interpretation of the test results

Negative for entire peanut IgE:

-Negative IgE results for entire peanut may indicate a lack of sensitization to peanut. Because IgE antibodies specific for entire peanut are not detectable, testing for peanut components is not performed.

Positive for entire peanut IgE/negative for peanut component IgE:

-Positive IgE results for entire peanut in the absence of detectable IgE responses to any peanut components may indicate a low to moderate sensitization to peanut.

Correlation with patient history of allergic or anaphylactic responses to peanut is recommended.

Positive for entire peanut IgE/positive for peanut component IgE:

-Positive IgE results to the storage proteins Ara h 1, Ara h 2, and Ara h 3 in the context of a positive IgE result for entire peanut may be associated with sensitization to peanut, with increased risk for allergic reaction upon exposure to peanut, and/or with a stronger risk for a systemic reaction.

-Positive IgE results to Ara h 8 in the context of a positive IgE result for entire peanut, but with negative antibodies to Ara h 1, Ara h 2, and Ara h 3, may be associated with cross-reactivity with birch and birch-related tree pollens and/or with an increased risk of a localized allergic reaction.

-Positive IgE results to Ara h 9 own been associated with both systemic and localized reactions, and with cross-reactivity to peach and peach-related fruits.


Special InstructionsLibrary of PDFs including pertinent information and forms related to the test

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. Gastrointestinal (eg, vomiting, diarrhea)
  2. Respiratory (eg, acute bronchospasm, rhinoconjunctivitis)
  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. Immulite (Siemens AG, Berlin, Germany)
  2. ImmunoCAP (Phadia AB, Uppsala, Sweden)
  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.

What is nut allergy?

An allergy occurs when your body’s immune system, which normally fights infection, overreacts to a substance called an allergen.

Most allergens are not obviously harmful and they own no effect on people who are not allergic to them. Allergic reactions to allergens can vary from mild to life-threatening.

Both peanuts and tree nuts (for example, walnuts, hazelnuts, almonds, cashews, pecans, Brazils and pistachios) can act as allergens, and can cause an allergic reaction in some people. When you come into contact with something that you are allergic to (an allergen), a group of cells in your body, called mast cells, release a substance called histamine. Histamine causes the tiny blood vessels in the tissues of your body to leak fluid which causes the tissues to swell.

This results in a number of diverse symptoms.

Strictly speaking, peanuts are not nuts, they are legumes, in the same family as peas and beans. Peanuts grow underground whereas other nuts grow on trees. The expression nut in this leaflet can mean either tree nuts or peanuts.

See also the separate leaflets calledAllergies and Food Allergy and Intolerance for more information about allergy in general.


Clinical InformationDiscusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Peanut allergy is one of the most common food allergies in the United States, with an estimated prevalence of approximately 1% to 2%.(1) The clinical symptoms of peanut allergy may range from relatively mild, such as rhinorrhea, pruritus, or nausea, to an anaphylactic reaction that is systemic and potentially life-threatening.

The diagnosis of peanut allergy is dependent upon the presence of compatible clinical symptoms in the context of peanut exposure, with support from identification of peanut-specific IgE antibodies, either by skin testing or in vitro serology testing. In vitro testing has generally focused on assessing for the presence of entire peanut IgE antibodies. These antibodies are identified by immunoassay in which the capture allergen is an extract prepared from natural peanut raw material.

Most studies own demonstrated a correlation between entire peanut IgE antibodies and an increased likelihood of a clinical allergic response. However, some patients with significantly elevated concentrations of entire peanut IgE antibodies do not own any reaction when istered a peanut oral food challenge. In some cases, this may be due to the presence of an IgE antibody specific for a nonallergenic protein present within the peanut extract.

This is the basis of component allergen testing, in which the presence of IgE antibodies specific for individual proteins, namely Ara h 1, Ara h 2, Ara h 3, Ara h 8, and Ara h 9, within the peanut extract are assessed. Ara h 1, 2, and 3 are seed storage proteins, and are the most relevant for evaluation of suspected peanut allergy.(2,3) Ara h 2, in specific, has the best sensitivity and specificity for clinically relevant peanut allergic disease. Ara h 1, 2, and 3-specific IgEs also tend to be associated with more severe allergic reactions. Ara h 9 is a member of the lipid transfer protein (LTP) family.

LTPs are ubiquitous throughout the plant kingdom, and are also extremely homologous. IgE antibodies specific for Ara h 9 may be associated with allergic reactions upon peanut ingestion, although published data on this is not conclusive.(4) In addition, because of the significant sequence homology, cross-reactivity of IgE antibodies may be observed between Ara h 9 and LTPs in commonly consumed plants such as peaches, apples, and plums. Lastly, Ara h 8 is a homologue of the birch pollen allergen Bet v 1.

What does class 4 peanut allergy mean

IgE antibodies against Ara h 8 are generally associated with milder peanut allergies and may be seen in the context of birch pollen sensitization.(5)


Testing AlgorithmDelineates situations when tests are added to the initial order. This includes reflex and additional tests.

Testing begins with analysis of peanut IgE. If peanut IgE is undetectable (< kU/L), testing is completed.

If peanut IgE is detectable (> or = kU/L), then the 5 peanut components (Ara h 2, Ara h 1, Ara h 3, Ara h 8, and Ara h 9) are performed at an additional charge.



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:

  • Anaphylaxis – Rapid onset, progressive, severe symptoms involving more than one organ system that can happen with IgE mediated food allergy.
  • 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.

  • 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. 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. 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.

What does class 4 peanut allergy mean

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.

What does class 4 peanut allergy mean

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.

What does class 4 peanut allergy mean

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.

  • 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.

  • 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.

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.

What does class 4 peanut allergy mean

You can follow him on @AllergyKidsDoc.

Medical review October and April

Useful ForSuggests clinical disorders or settings where the test may be helpful

Evaluation of patients with suspected peanut allergy

Evaluation of patients with possible peanut cross-reactivity

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

Useful ForSuggests clinical disorders or settings where the test may be helpful

Evaluation of patients with suspected peanut allergy

Evaluation of patients with possible peanut cross-reactivity


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