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Blood Test Tracker

Peanut IgE

Measures IgE antibodies to whole peanut in your blood. A detectable result means you are sensitized to peanut, which is not the same as a peanut allergy.

AI-verified against cited sources. Awaiting expert reviewAlso called f13, f013LOINC 6206-7

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What it is

IgE is a type of antibody your immune system can make against a food protein. This test measures IgE to an extract of whole peanut using a method called ImmunoCAP (also written f13 or f013). The extract holds many peanut proteins, so it is a broad first look. Results come in kilounits per liter (kU/L), and many labs also print a class from 0 to 6. Peanut is a legume, like soy and lentils, not a tree nut.

Why it matters

Peanut allergy is one of the most common food allergies in the United States, affecting an estimated 1 to 2% of people. Reactions can range from mild to life-threatening. This test can help you and your clinician look at whether peanut might be behind symptoms such as hives, stomach upset or mouth itching. On its own it cannot confirm an allergy, because some people with a detectable level eat peanut without trouble. In general, higher levels go with a higher chance of reacting, but the number does not predict how serious a reaction would be. Your history matters most, and sometimes a supervised food challenge is the way to find out.

If it’s high

A level above your lab's range means your immune system has made IgE to peanut proteins. In general, higher levels make a reaction to peanut more likely, but the link is not exact. Some people with high levels eat peanut with no problem, and some people with low or even undetectable levels do react. The number does not say how severe a reaction would be.

Common causes

  • Sensitization without symptoms, where you make the antibody but eat peanut with no problem
  • A true peanut allergy
  • IgE to a mild peanut protein, such as Ara h 8, which is linked to birch pollen allergy
  • Cross-reacting IgE from other legumes or tree nuts, whose proteins look similar to peanut's
  • IgE to a harmless protein in the test extract
  • A very high total IgE (above about 2,500 kU/L), which can cause a false-positive reading

What can help

  • Talk with an allergist about how this result fits your history of eating peanut or foods that may contain it
  • Ask whether peanut component tests, such as Ara h 2, or a supervised food challenge would help clarify your result
  • Keep notes on any symptoms after peanut or foods that contain it, including how soon they began
  • If you have been told to avoid peanut, follow the plan your clinician gave you and ask about reading food labels

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: 0–0.09 kU/L. Source: Mayo Clinic Laboratories, ARUP Laboratories, U.S. Food and Drug Administration, Journal of Allergy and Clinical Immunology, Clinical & Experimental Allergy, MedlinePlus, National Library of Medicine.

ImmunoCAP IgE classes (ARUP labels; Mayo Clinic Laboratories class edges)

  • Class 0: no significant level detectedbelow 0.1 kU/L
  • Class 0/1: clinical relevance undetermined0.1 to under 0.35 kU/L
  • Class 1: low0.35 to under 0.7 kU/L
  • Class 2: moderate0.7 to under 3.5 kU/L
  • Class 3: high3.5 to under 17.5 kU/L
  • Class 4: very high17.5 to under 50 kU/L
  • Class 5: very high50 to under 100 kU/L
  • Class 6: very high100 and above kU/L

NIAID 2017 peanut-introduction guidance for infants with severe eczema or egg allergy

  • Below 0.35 kUA/L: peanut allergy unlikely (strong negative predictive value)below 0.35 kU/L
  • 0.35 kUA/L or higher: specialist visit advised; not enough on its own to show peanut allergy0.35 and above kU/L

What can affect your result

  • Age: most studies of peanut IgE were done in children, and in children a falling level over time is often a sign that tolerance is starting
  • Birch or other pollen allergy, which can cause IgE to mild peanut proteins
  • Allergy to other legumes or tree nuts, which can cause cross-reacting IgE
  • A very high total IgE (above about 2,500 kU/L) can cause false-positive results
  • The lab and test brand: results and predictive values found with one system cannot be applied to another
  • Where a lab draws its cutoff (0.10, 0.35 or 0.70 kU/L)
  • A very high total IgE (above about 2,500 kU/L) can cause false-positive results through nonspecific binding (Mayo Clinic Laboratories).
  • Antihistamines do not affect this blood test the way they affect skin-prick testing (NIAID 2010), but follow your clinician's instructions about any medicine before the test.
  • Some people with a high total peanut IgE eat peanut or pass a food challenge, which may be due to IgE against a harmless protein in the test extract (Mayo Clinic Laboratories).
  • Different labs and test brands give different numbers for the same blood sample, so compare results from the same lab and system.

When to talk to a clinician

Call 911 or your local emergency number if, after eating peanut or a food that may contain it, you have trouble breathing, swelling of the lips, tongue or throat, dizziness or fainting, or severe stomach pain with vomiting. Talk with a clinician or allergist about milder symptoms, such as hives or mouth itching, even if this result is in the usual range.

Questions you could ask

  • How often, if at all, should we recheck this?
  • Could my pollen allergy be part of this result?
  • How does this result fit with what happens when I eat peanut?
  • Would a peanut component test, such as Ara h 2, or a supervised food challenge help clarify things?
  • Do I need to avoid tree nuts or other legumes too?
  • Should I have a plan for accidental exposure?

Questions people ask

Does a positive peanut IgE mean I am allergic to peanut?

Not by itself. The test shows that your immune system has made IgE to peanut, which is called sensitization. An expert panel convened by the NIAID says these blood tests alone cannot confirm a food allergy. Your clinician looks at the result with your history of eating peanut, and sometimes a supervised food challenge.

Does a higher number mean a worse reaction?

Not exactly. Higher levels make a reaction more likely, but MedlinePlus notes that the amount of IgE does not predict how serious an allergy may be. The number says more about the odds of reacting than about how severe a reaction would be.

My result is negative. Can I rule out a peanut allergy?

Not always. A negative result makes an IgE-mediated peanut allergy less likely, but undetectable levels do sometimes occur in people who react. An expert panel says that when the history is highly suggestive, a physician-supervised food challenge is needed before telling someone they are not allergic. Tell your clinician about any symptoms after peanut, even when this result is negative.

How is whole-peanut IgE different from Ara h 2?

The whole-peanut test uses a mix of many peanut proteins, so it can be detectable even when you eat peanut without trouble. Ara h 2 is a single peanut protein that is most closely tied to true peanut allergy, so a component test can help sort out an unclear result. Neither replaces your history or a supervised food challenge.

My infant has eczema. What does the 0.35 cutoff mean?

For infants with severe eczema, egg allergy or both, a US expert panel (NIAID, 2017) advises considering peanut IgE and/or skin testing before peanut is introduced. Early introduction lowers the risk of peanut allergy in high-risk infants. The panel says a result under 0.35 kUA/L makes peanut allergy unlikely, while 0.35 or higher should lead to a specialist visit. A result at or above 0.35 does not by itself mean your baby is allergic. Talk with your child's clinician before feeding peanut to a high-risk infant.

Show the science and sources

For clinicians and researchers

Quantitative allergen-specific IgE to a whole peanut extract (ImmunoCAP f13) by fluoroenzyme immunoassay. Mayo and ARUP both list LOINC 6206-7. The ImmunoCAP Specific IgE system reports up to 100 kUA/L with a limit of quantitation of 0.1 kUA/L, is traceable to the WHO IgE reference (IRP 75/502 or 3rd IS 11/234), and its maker recommends a 0.35 kUA/L cutoff while telling each lab to set its own range (FDA review K173726). Allergen-specific IgE shows sensitization, not clinical allergy. Higher levels go with a higher probability of reaction, but predictive values varied between studies, cutoffs defined as 95% predictive values may be more predictive than skin prick tests in some populations, and undetectable IgE occasionally occurs in IgE-mediated food allergy (NIAID 2010, Guideline 7). ImmunoCAP, Turbo-MP and Immulite gave significantly different values for the same samples, so predictive values cannot be moved between systems (NIAID 2010). In the HealthNuts infant cohort (100 allergic and 100 tolerant infants), the previously published 95% positive predictive value of 15 kUA/L for whole-peanut IgE had a specificity of 98% but found only 26% of infants with true peanut allergy, while Ara h 2 IgE found 60% at the same specificity (Dang 2012). A systematic review of 22 studies, 21 in children, called the accuracy of peanut extract IgE and skin tests suboptimal and found the best accuracy for Ara h 2 (Klemans 2015). Mayo lists Ara h 1, 2, 3 and 6 as stable storage proteins linked to whole-body reactions, Ara h 8 as a birch-pollen-related protein linked to local mouth symptoms, and Ara h 9 as a lipid transfer protein; in 144 children sensitized to Ara h 8 but not to Ara h 1, 2 or 3, 89.5% ate peanut or passed a challenge (Asarnoj 2012). Mayo also notes that some patients with significantly raised total peanut IgE pass an oral challenge, possibly because of IgE to a nonallergenic protein in the extract. For infants with severe eczema, egg allergy or both, the NIAID addendum (2017) advises considering peanut IgE and/or skin testing before early introduction: IgE under 0.35 kUA/L has strong negative predictive value, while 0.35 or higher lacks adequate positive predictive value and calls for specialist referral. In LEAP, among 530 infants with a negative baseline skin test, 13.7% of the avoidance group and 1.9% of the early-consumption group had peanut allergy at 60 months. In children, a falling sIgE is often a marker of tolerance, a high initial level goes with a lower rate of resolution, and far fewer children outgrow peanut or tree nut allergy than milk, egg, soy or wheat allergy (NIAID 2010). Mayo notes false positives can occur above about 2,500 kU/L total IgE.

LOINC 6206-7 (primary), 112151-6. Specimen: serum.

Sources

  1. Peanut, IgE, Serum (test ID PEAN), Mayo Clinic Laboratories
  2. Peanut, IgE with Reflex to Peanut Components, IgE, Serum (test ID PEANT), Mayo Clinic Laboratories
  3. Allergen, Food, Peanut (ARUP test 0055024), ARUP Laboratories
  4. 510(k) Decision Memorandum K173726: ImmunoCAP Specific IgE (ImmunoCAP Allergen f447, rAra h 6, Peanut), U.S. Food and Drug Administration (2018)
  5. Guidelines for the diagnosis and management of food allergy in the United States: report of the NIAID-sponsored expert panel, Journal of Allergy and Clinical Immunology (2010)
  6. Allergy Blood Test, MedlinePlus, National Library of Medicine
  7. Addendum guidelines for the prevention of peanut allergy in the United States: Report of the National Institute of Allergy and Infectious Diseases-sponsored expert panel, Journal of Allergy and Clinical Immunology (2017)
  8. Increasing the accuracy of peanut allergy diagnosis by using Ara h 2, Journal of Allergy and Clinical Immunology (2012)
  9. Diagnostic accuracy of specific IgE to components in diagnosing peanut allergy: a systematic review, Clinical & Experimental Allergy (2015)
  10. Peanut component Ara h 8 sensitization and tolerance to peanut, Journal of Allergy and Clinical Immunology (2012)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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