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Blood Test Tracker

Ana o 3 (cashew) IgE

Measures IgE to Ana o 3, a protein stored in cashew seeds. Higher levels are more common in people with true cashew allergy, including strong reactions.

AI-verified against cited sources. Awaiting expert reviewAlso called f443, rAna o 3LOINC 82539-8

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What it is

Ana o 3 is a protein that stores energy in the cashew seed. It belongs to a family called 2S albumins. Labs measure IgE to Ana o 3 on its own (ImmunoCAP f443), often as a follow-up after a whole-cashew IgE test is detectable. Labcorp, for example, runs it automatically when the cashew IgE is above 0.10 kU/L. Results come in kilounits per liter (kU/L), and many labs also print a class from 0 to 6.

Why it matters

A whole-cashew test can be detectable in people who are not truly allergic, for example because of pollen proteins or shared sugar structures. Ana o 3 is one specific cashew seed protein, so testing for it can help sort out those cases. Labcorp notes that IgE to Ana o 3 is associated with reactions that affect the whole body, and that cashew and pistachio are closely related and often cross-react. Even so, the result is one piece of the picture. Your history and, sometimes, a supervised food challenge decide whether you react.

If it’s high

A level above your lab's range means your immune system has made IgE to the cashew protein Ana o 3. Higher levels are more common in people who are truly allergic to cashew, including people who have strong reactions, and may also go with allergy to pistachio. It does not predict exactly how you would react, and your clinician reads it with your history.

Common causes

  • Sensitization without symptoms, where the antibody is present but cashew is tolerated
  • Cross-reacting IgE from pistachio, which is closely related to cashew
  • True (primary) cashew allergy
  • 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 and whether a supervised food challenge makes sense
  • Ask whether related nuts, such as pistachio, walnut and peanut, should be looked at too
  • If you have been told to avoid cashew, ask which foods can hide it, such as nut butters, pesto, baked goods and some Asian dishes

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, Labcorp, Allergy, U.S. Food and Drug Administration, Journal of Allergy and Clinical Immunology.

ImmunoCAP IgE classes (Mayo Clinic Laboratories cashew component wording)

  • Class 0: negativebelow 0.1 kU/L
  • Class 0/1: equivocal or borderline0.1 to under 0.35 kU/L
  • Class 1: low positive0.35 to under 0.7 kU/L
  • Class 2: moderate positive0.7 to under 3.5 kU/L
  • Class 3: high positive3.5 to under 17.5 kU/L
  • Class 4: very high positive17.5 to under 50 kU/L
  • Class 5: very high positive50 to under 100 kU/L
  • Class 6: very high positive100 and above kU/L

What can affect your result

  • Whole-cashew IgE can be detectable for other reasons, such as pollen proteins or shared sugar structures, while Ana o 3 stays undetectable
  • Allergy to other nuts, especially pistachio, which can cross-react
  • Age and how recently cashew was eaten or avoided
  • 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 (a caution Mayo Clinic Laboratories lists for its peanut and other allergen IgE tests).
  • 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 cashew 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

  • What should I know about cashew that is hidden in foods?
  • How often, if at all, should we recheck this?
  • How does this result fit with my whole-cashew IgE and my history?
  • Should other nuts, such as pistachio, walnut or peanut, be looked at too?
  • Would a supervised food challenge help clarify my result?
  • My Ana o 3 is in the usual range but my whole-cashew test is not. What does that mean for me?

Questions people ask

Why was this test ordered after my cashew test?

A whole-cashew test can be detectable for reasons other than a true allergy, such as pollen proteins or shared sugar structures. Ana o 3 is a specific cashew seed protein, so a result for it can help sort out those cases. Some labs add it automatically when the cashew test is above 0.10 kU/L.

Can I still be allergic to cashew if my Ana o 3 is in the usual range?

Possibly. Cashew has other proteins that can bind IgE, and blood tests alone cannot rule out an allergy, so a result in the usual range does not settle the question. Your clinician weighs it with your history and other tests.

Does roasting or cooking cashews make them safe?

Labcorp advises that people sensitized to Ana o 3 should avoid roasted or heated cashews as well as raw ones. Ask your allergist what this means for you.

Show the science and sources

For clinicians and researchers

Quantitative IgE to recombinant Ana o 3 (ImmunoCAP f443), a 2S albumin seed storage protein, by fluoroenzyme immunoassay. Mayo prints a reference value of <0.10 kU/L and ARUP prints 0.09 kU/L or lower. In a multicentre study of 61 children (42 cashew-allergic), Ana o 3 sIgE separated allergic from tolerant children better than cashew extract sIgE (area under the curve 0.94 vs 0.78), and a 95% probability of allergy was estimated at 2.0 kU/L (Lange 2017). Cutoffs differ between studies and populations and do not transfer between assay brands (NIAID 2010). Labcorp states that sensitization to Ana o 3 indicates primary cashew allergy and that 2S albumins are associated with systemic reactions. People sensitized to Ana o 3 are advised to avoid raw as well as roasted or heated cashew, and to be assessed for pistachio, walnut and peanut. A positive whole-cashew IgE with a negative Ana o 3 may reflect other cashew storage proteins, lipid transfer protein, PR-10 or profilin pollen proteins, or cross-reactive carbohydrate determinants (Labcorp). Cashew and pistachio show extensive cross-reactivity, and NIAID reports higher sIgE correlations between cashew and pistachio. Mayo's peanut IgE listing cautions that false positives can occur above about 2,500 kU/L total IgE; its cashew component page does not repeat this.

LOINC 82539-8 (primary), 113002-0. Specimen: serum.

Sources

  1. Cashew Component rAna o 3 (test ID FCCA3), Mayo Clinic Laboratories
  2. Allergen, Food, Cashew Component rAna o 3, IgE (ARUP test 3018561), ARUP Laboratories
  3. Allergen Profile, Cashew Nut, IgE With Component Reflex (Labcorp test 604159), Labcorp
  4. Ana o 3-specific IgE is a good predictor for clinically relevant cashew allergy in children, Allergy (2017)
  5. 510(k) Decision Memorandum K173726: ImmunoCAP Specific IgE (ImmunoCAP Allergen f447, rAra h 6, Peanut), U.S. Food and Drug Administration (2018)
  6. 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)
  7. Peanut, IgE with Reflex to Peanut Components, IgE, Serum (test ID PEANT), Mayo Clinic Laboratories

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

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