Evaluation of patients with suspected peanut allergy
Evaluation of patients with possible peanut cross-reactivity
The determination of the relative amount of IgE antibody to total peanut, and IgE antibodies to specific peanut components, can aid in assessment of the potential strength and type of allergenic response to peanuts.
IgE antibody to total peanut extract will be tested.
If detectable total peanut IgE antibody is present, additional specific peanut allergen antibody testing will be performed. This is comprised of testing for IgE antibodies to the potential allergens Ara h 2, Ara h 1, Ara h 3, Ara h 6, Ara h 8, Ara h 9, and profilin Bet v2.
| Test Id | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| PNTCP | Peanut Components, IgE, S | No | No |
Testing begins with analysis of peanut IgE. If peanut IgE is negative (<0.10 kU/L), testing is complete.
If peanut IgE is 0.10 kU/L or greater, then 7 peanut components (Ara h 2, Ara h 1, Ara h 3, Ara h 6, Ara h 8, Ara h 9, and profilin Bet v2) are performed at an additional charge.
Fluorescent Enzyme Immunoassay (FEIA)
Ground Nut
Monkey Nut
Glycinin (h 1 and h 3)
Conglutin (h 2)
A bet v 1-homologous allergen (h 8)
Group 1 Fagales-related protein (h 8)
PR-10 Protein (h 8)
Non-specific Lipid Transfer Protein (ns-LTP) (h 9)
PR-14 Protein (h 9)
Bet v2
Profilin
Testing begins with analysis of peanut IgE. If peanut IgE is negative (<0.10 kU/L), testing is complete.
If peanut IgE is 0.10 kU/L or greater, then 7 peanut components (Ara h 2, Ara h 1, Ara h 3, Ara h 6, Ara h 8, Ara h 9, and profilin Bet v2) are performed at an additional charge.
Serum
For a listing of allergens available for testing, see Allergens - Immunoglobulin E (IgE) Antibodies in Special Instructions
Container/Tube:
Preferred: Red top
Acceptable: Serum gel
Specimen Volume: 2 mL
If not ordering electronically, complete, print, and send an Allergen Test Request (T236) with the specimen.
0.75 mL
| Gross hemolysis | OK |
| Gross lipemia | OK |
| Gross icterus | OK |
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum | Refrigerated (preferred) | 14 days | |
| Frozen | 90 days | ||
| Ambient | 7 days |
Evaluation of patients with suspected peanut allergy
Evaluation of patients with possible peanut cross-reactivity
Testing begins with analysis of peanut IgE. If peanut IgE is negative (<0.10 kU/L), testing is complete.
If peanut IgE is 0.10 kU/L or greater, then 7 peanut components (Ara h 2, Ara h 1, Ara h 3, Ara h 6, Ara h 8, Ara h 9, and profilin Bet v2) are performed at an additional charge.
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 a systemic and potentially life-threatening anaphylactic reaction. 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 potential peanut-specific IgE allergen antibodies, either by skin testing or in vitro serology testing. In vitro testing has generally focused on assessing for the presence of total 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 have demonstrated a correlation between total peanut IgE allergen antibodies and an increased likelihood of a clinical allergic response.
Once an elevated antibody response to total peanut IgE extract is established, assessment for the presence of specific IgE antibodies to the most common peanut allergenic components will be performed.
During peanut component allergen testing the presence of IgE antibodies specific for potentially allergenic individual proteins, namely Ara h 1, Ara h 2, Ara h 3, Ara h 6, Ara h 8, Ara h 9, and profilin protein Bet v2, are assessed. The determination of the relative amount of IgE antibody to specific peanut components can aid in assessment of the potential strength and type of allergenic response (see Table below).
Ara h 1, 2, 3, and 6 are seed storage proteins and are the most relevant for evaluation of suspected peanut allergy.(2,3) The presence of antibodies to Ara h 2, in particular, exhibits strong association with potential systemic reactions. Ara h 1, 2, and 3-specific IgE antibodies tend to be associated with more severe allergic reactions. Ara h6 shares substantial, but not complete, cross-reactivity with Ara h2, and often exhibits similarity in terms of the degree and type of allergenicity.
Immunoglobulin E antibodies against Ara h 8 are generally associated with milder peanut allergies and may be seen in the context of birch pollen sensitization. Ara h 8 is a homologue of the birch pollen allergen Bet v1.(4) Ara h 9 is a member of the lipid transfer protein (LTP) family. LTP is ubiquitous throughout the plant kingdom and is 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.(5) In addition, because of the significant sequence homology, cross-reactivity of IgE antibodies may be observed between Ara h 9 and LTP in commonly consumed plants such as peaches, apples, and plums.
Finally, IgE antibodies to the profilin Bet v2, while associated with birch pollen sensitivity, also represent a minor peanut allergen marker as it is cross-reactive with the peanut profilin, Ara h5. As profilin proteins are present in many other foods, sensitivity to profilin Bet v2 may be associated in broad allergen cross-reactivity among foods, including mango, peach, apple, hazelnut, celery, carrot, paprika, anise, fennel, coriander, cumin, tomato, and potato. The presence of antibodies to profilin Bet v2 is typically associated with milder allergic reactions and oral allergy syndrome.
Table of Specific Peanut Allergens
| Allergen | Most common reaction type | Heat and digestion stability | Selected potential cross-reactivity with other allergens |
| Ara h1 (storage peanut protein) | Systemic | Stable | Some potential allergenic cross reactivity with plant vicilins, including those found in soy and pea |
| Ara h2 (storage peanut protein) | Systemic | Strongly stable | Some potential allergenic cross reactivity with almond and brazil nut allergens Ara h6 |
| Ara h3 (storage peanut protein) | Systemic | Stable | Some potential allergenic cross reactivity with hazelnut and soybean allergens |
| Ara h6 (storage peanut protein) | Systemic | Strongly stable | Ara h2 |
| Ara h8 (PR-10 protein, Bet v 1-homologous allergen) | Associated with local reactions such as oral allergy syndrome (OAS) | Labile to heat and digestion | Associated with allergy to birch and birch related tree pollen |
| Ara h9 (lipid transfer protein) | Associated with both systemic reactions and local reactions such as OAS | Stable | Associated with allergy to peach and peach related fruits |
| Profilin Bet v2 | Associated with more minor local reactions such as OAS | Labile to heat and digestion | Associated with allergy to a broad variety of pollen and plant products from trees, nuts, grasses, and weeds |
| Class | IgE kU/L | Interpretation |
| 0 | <0.10 | Negative |
| 0/1 | 0.10-0.34 | Borderline / Equivocal |
| 1 | 0.35-0.69 | Equivocal |
| 2 | 0.70-3.49 | Positive |
| 3 | 3.50-17.4 | Positive |
| 4 | 17.5-49.9 | Strongly positive |
| 5 | 50.0-99.9 | Strongly positive |
| 6 | > or =100 | Strongly positive |
Concentrations > or =0.70 kU/L (Class 2 and above) will flag as abnormally high.
When detectable total peanut IgE antibody is present (> or =0.10 IgE kUa/L), additional specific component IgE antibody testing will be performed. If at least one potential specific allergenic peanut component IgE is detectable (> or =0.10 IgE kUa/L), an interpretative report will be provided.
When the sample is negative for total peanut IgE antibody (<0.10 IgE kUa/L), further testing for specific peanut component IgE antibodies will not be performed. Negative IgE results for total peanut antibody may indicate a lack of sensitization to potential peanut allergenic components.
Results from peanut specific IgE antibody testing must be interpreted in the context of patient’s clinical evaluation and history of allergen exposures.
Negative results for IgE to total peanut and any peanut components do not completely exclude the possibility of clinically relevant allergic responses upon exposure to peanut. Clinical correlation of results from in vitro IgE testing with patient history of allergic or anaphylactic responses to peanut is recommended.
Positive results for IgE to total peanut or any potential peanut allergenic components are not diagnostic for peanut allergy, and only indicate patient may be sensitized to peanut or a cross-reactive allergen. Clinical correlation of results from in vitro IgE testing with patient history of allergic or anaphylactic responses to peanut is recommended.
Testing for IgE antibodies may not useful in patients previously treated with immunotherapy to determine if residual clinical sensitivity exists, or in patients in whom the medical management does not depend upon identification of allergen specificity.
Some patients with significantly elevated concentrations of total peanut IgE antibodies do not have any reaction when administered a peanut oral food challenge. This may be due to the presence of an IgE antibody specific for a nonallergenic protein present within the peanut extract. Furthermore, some individuals with clinically insignificant or no sensitivity to allergens may have detectable levels of IgE antibodies in serum; therefore results must be interpreted in the clinical context.
False-positive results for IgE antibodies may occur in patients with markedly elevated serum IgE (>2500 kU/L) due to nonspecific binding to allergen solid phases.
1. Sicherer SH, Wood RA: Advances in diagnosing peanut allergy. J Allergy Clin Immunol Pract. 2013 Jan;1(1):1-13. doi: 10.1016/j.jaip.2012.10.004
2. Eller E, Bindslev-Jensen C: Clinical value of component-resolved diagnostics in peanut-allergic patients. Allergy. 2013 Feb;68(2):190-194. doi: 10.1111/all.12075
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. 2012 Dec;67(12):1538-1546. doi: 10.1111/all.12047
4. Asarnoj A, Nilsson C, Lidholm J, et al: Peanut component Ara h 8 sensitization and tolerance to peanut. J Allergy Clin Immunol. 2012 Aug;130(2):468-472. doi: 10.1016/j.jaci.2012.05.019
5. Klemans RJ, van Os-Medendorp H, Blankestijn M, Bruijzeel-Koomen CA, Knol EF, Knulst AC: Diagnostic accuracy of specific IgE to components in diagnosing peanut allergy: a systematic review. Clin Exp Allergy. 2015 Apr;45(4):720-730. doi: 10.1111/cea.12412
6. Koid AE, Chapman MD, Hamilton RG, et al: Ara h 6 complements Ara h 2 as an important marker for IgE reactivity to peanut. J Agric Food Chem. 2014 Jan 8;62(1):206-213. doi:10.1021/jf4022509
7. Bublin M, Breiteneder H: Cross-reactivity of peanut allergens. Curr Allergy Asthma Rep. 2014 Apr;14(4):426. doi: 10.1007/s11882-014-0426-8
8. Chan ES, Greenhawt MJ, Fleischer DM, Caubet JC: Managing cross-reactivity in those with peanut allergy. J Allergy Clin Immunol Pract. 2019 Feb;7(2):381-386. doi: 10.1016/j.jaip.2018.11.012
9. Simberloff T, Parambi R, Bartnikas LM, el al: Implementation of a standardized clinical assessment and management plan (SCAMP) for food challenges. J Allergy Clin Immunol Pract. 2017 Mar-Apr;5(2):335-344. doi:10.1016/j.jaip.2016.05.021
Specific IgE from the patient's serum reacts with the allergen of interest, which is covalently coupled to an ImmunoCAP. After washing away nonspecific IgE, enzyme-labeled anti-IgE antibody is added to form a complex. After incubation, unbound anti-IgE is washed away and the bound complex is then incubated with a developing agent. After stopping the reaction, the fluorescence of the eluate is measured. Fluorescence is proportional to the amount of specific IgE present in the patient's sample (ie, the higher the fluorescence value, the more IgE antibody is present).(Package insert: ImmunoCAP System Specific IgE FEIA. Phadia; Rev 06/2019)
Monday through Friday
This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.
86003
| Test Id | Test Order Name | Order LOINC Value |
|---|---|---|
| PEANT | Peanut Component Reflex, S | 6206-7 |
| Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
|---|---|---|
| PNUT | Peanut, IgE, S | 6206-7 |