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Ara h 8 (peanut) IgE

Measures IgE to Ara h 8, a peanut protein that looks like a birch pollen protein. It is generally linked to milder, mouth-area symptoms, though stronger reactions are not ruled out.

AI-verified against cited sources. Awaiting expert reviewAlso called f352, rAra h 8LOINC 63477-4

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What it is

Ara h 8 is a protein in peanut that is very similar to Bet v 1, the main allergen in birch pollen. People with birch pollen allergy can make IgE that also recognizes Ara h 8. Ara h 8 is generally broken down by heat and digestion, so it tends to cause itching or tingling in the mouth rather than whole-body reactions. Labs measure it on its own (ImmunoCAP f352), usually after a whole-peanut IgE test is detectable.

Why it matters

A whole-peanut test can be detectable because of Ara h 8 alone. In a study of 144 children who were sensitized to Ara h 8 but not to Ara h 1, 2 or 3, about 9 in 10 either ate peanut regularly or passed a peanut challenge, and about 1 in 10 had mouth symptoms only. So Ara h 8 on its own usually points to a milder pattern. It is still one piece of the picture, and rare reactions can happen, so your clinician reads it with your other peanut results and your history.

If it’s high

A level above your lab's range means your immune system has made IgE to Ara h 8. It often goes along with birch pollen allergy. If this is the only peanut component that is detectable, the pattern is usually mild, such as itching or tingling in the mouth, if there are any symptoms. If Ara h 2 or other peanut seed proteins are also detectable, the picture is different, so your clinician reads the components together.

Common causes

  • Birch pollen allergy, since Ara h 8 closely resembles the main birch pollen allergen
  • Allergy to other pollens related to birch
  • Sensitization without symptoms, where peanut is eaten with no problem
  • 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 your Ara h 8 result fits with your other peanut component results
  • Ask whether birch pollen allergy is the likely source
  • Tell your clinician about any itching or tingling in your mouth after peanuts, nuts or fresh fruit, and how it changes with the pollen season
  • Ask how to check safely whether you tolerate peanut, rather than deciding from one result

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, UW Medicine Laboratory Medicine & Pathology, Quest Diagnostics, U.S. Food and Drug Administration, Journal of Allergy and Clinical Immunology, Clinical & Experimental Allergy.

ImmunoCAP IgE classes (Mayo Clinic Laboratories wording)

  • Class 0: negativebelow 0.1 kU/L
  • Class 0/1: borderline or equivocal0.1 to under 0.35 kU/L
  • Class 1: equivocal0.35 to under 0.7 kU/L
  • Class 2: positive0.7 to under 3.5 kU/L
  • Class 3: positive3.5 to under 17.5 kU/L
  • Class 4: strongly positive17.5 to under 50 kU/L
  • Class 5: strongly positive50 to under 100 kU/L
  • Class 6: strongly positive100 and above kU/L

What can affect your result

  • Birch and related tree pollen allergy
  • Which other peanut components are present, such as Ara h 2, which change how the result is read
  • Age, since most studies of Ara h 8 were done in children
  • A very high total IgE (above about 2,500 kU/L) can cause false-positive results
  • The lab and test brand, because results from different systems are not directly comparable
  • 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).
  • Different labs and test brands give different numbers for the same blood sample, so compare results from the same lab and system.

Slow. It usually shifts over months to years, not weeks.

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

  • Should we look at pollen allergies as part of this?
  • Does my Ara h 8 result fit with a birch pollen allergy?
  • How do my other peanut component results change the picture?
  • How can we safely check whether I tolerate peanut?
  • My Ara h 8 is in the usual range but my whole-peanut IgE is not. What does that mean for me?

Questions people ask

I only have Ara h 8, not Ara h 2. Does that mean peanut is safe for me?

It often points to a milder pattern. In one study of 144 children with IgE to Ara h 8 only, almost 9 in 10 ate peanut or passed a challenge, and about 1 in 10 had mouth symptoms only. Rare reactions still happen, so ask your allergist how to confirm that you tolerate peanut.

Why is Ara h 8 linked to birch pollen?

Ara h 8 has a shape very similar to Bet v 1, the main birch pollen allergen. IgE made against birch pollen can also bind Ara h 8, which is why people with birch pollen allergy can have a detectable peanut result.

Show the science and sources

For clinicians and researchers

Quantitative IgE to recombinant Ara h 8 (ImmunoCAP f352), a PR-10 protein homologous to the birch pollen allergen Bet v 1 that is labile to heat and digestion and associated with local reactions such as oral allergy syndrome (Mayo). In 144 children sensitized to Ara h 8 (0.35 kUA/L or more) but not to Ara h 1, 2 or 3 (under 0.35 kUA/L), 129 (89.5%) were peanut consumers or did not react to challenge and 14 (9.7%) had oral symptoms only; one boy with an earlier mild systemic reaction had lip swelling, stomach cramping and tiredness at a double-blind challenge. The authors concluded that isolated Ara h 8 sensitization indicates tolerance to peanut in almost all cases, while other, unidentified peanut determinants might cause symptoms in rare cases (Asarnoj 2012). In a systematic review, Ara h 8 and Ara h 9 had the weakest diagnostic accuracy for peanut allergy, and Ara h 2 the best (Klemans 2015). Cutoffs do not transfer between assay brands (NIAID 2010). Mayo notes false positives can occur above about 2,500 kU/L total IgE.

LOINC 63477-4 (primary), 112864-4. Specimen: serum.

Sources

  1. Peanut, IgE with Reflex to Peanut Components, IgE, Serum (test ID PEANT), Mayo Clinic Laboratories
  2. Mild Peanut IgE Ara h 8 (lab code RPTAH8), UW Medicine Laboratory Medicine & Pathology (2026)
  3. Peanut Component Panel (Quest test code 91681), Quest Diagnostics
  4. Diagnostic accuracy of specific IgE to components in diagnosing peanut allergy: a systematic review, Clinical & Experimental Allergy (2015)
  5. Peanut component Ara h 8 sensitization and tolerance to peanut, Journal of Allergy and Clinical Immunology (2012)
  6. 510(k) Decision Memorandum K173726: ImmunoCAP Specific IgE (ImmunoCAP Allergen f447, rAra h 6, Peanut), U.S. Food and Drug Administration (2018)
  7. 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)

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

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