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Blood Test Tracker

Hazelnut (Filbert) IgE

Measures IgE antibodies to hazelnut. A raised result can reflect a true hazelnut allergy or a milder pattern linked to birch pollen allergy.

AI-verified against cited sources. Awaiting expert reviewAlso called f17, f017LOINC 6136-6

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What it is

This test measures IgE antibodies to hazelnut, also called filbert (ImmunoCAP f17). Hazelnut allergy comes in two main forms. One is an itchy mouth and throat that happens in some people with birch pollen allergy, because hazelnut has a protein that looks like a birch pollen protein. The other is a reaction to hazelnut proteins that survive cooking and digestion, which can be more serious. This test looks at hazelnut as a whole, so it cannot tell the two apart on its own.

Why it matters

Knowing which type of hazelnut sensitization you have matters, because the chance of a serious reaction differs between them. That is why some labs add tests for individual hazelnut proteins (components) when this result is detectable. Your result is read together with your history of reactions, and sometimes a supervised food challenge. A detectable result alone does not confirm an allergy.

If it’s high

A level above your lab's range means your body has made more IgE to hazelnut. It shows sensitization. Whether it comes from the milder birch-pollen pattern or from true hazelnut allergy cannot be told from this number alone.

Common causes

  • Birch pollen allergy, which often goes with IgE to hazelnut and usually causes itching in the mouth and throat
  • A true hazelnut allergy
  • IgE that also reacts with similar proteins in other nuts, peanut or some fruits such as peach
  • Sensitization without symptoms
  • A very high total IgE (above about 2,500 kU/L), which can cause a false-positive reading

What can help

  • Ask an allergist whether tests for hazelnut components (Cor a 1, Cor a 8, Cor a 9 and Cor a 14) would help show which type you have
  • Ask what to do about hazelnut and other nuts while you wait for answers, and follow the plan your clinician gives you
  • If you have birch pollen allergy, ask whether your hazelnut result could be related to it

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.

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 pollen allergy, which is strongly linked to hazelnut sensitization
  • Cross-reactivity with other nuts, peanut and some fruits that have similar proteins
  • 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
  • Where a lab draws its cutoff (0.10, 0.35 or 0.70 kU/L)
  • Birch pollen allergy can raise hazelnut IgE through similar proteins, without a true hazelnut allergy (Mayo Clinic Laboratories).
  • A very high total IgE (above about 2,500 kU/L) can cause false-positive results through nonspecific binding (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.
  • Some labs reject hemolyzed, icteric or lipemic samples (ARUP).

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

When to talk to a clinician

Call 911 or your local emergency number right away if any of these happen after eating hazelnut or a food that may contain it: trouble breathing, swelling of the lips, tongue or throat, dizziness or fainting, repeated vomiting, or widespread hives. Do not wait for a lab result. For milder or past symptoms, talk with a clinician or allergist even if this result is in the usual range. Itching limited to the mouth after hazelnut is also worth mentioning to your clinician.

Questions you could ask

  • Should I have a plan in case of an accidental exposure?
  • Could my hazelnut result be related to birch pollen?
  • Would hazelnut component tests help show which type I have?
  • What should I do about other tree nuts and peanut?
  • My result is in the usual range but I have had symptoms after hazelnut. What should we do next?

Questions people ask

Why is my hazelnut result positive when I have birch pollen allergy?

Hazelnut contains a protein similar to the main birch pollen allergen, so IgE made against birch can also react to hazelnut. In many people this causes mostly itching in the mouth and throat, but not always, so your clinician may suggest tests for individual hazelnut proteins.

What are hazelnut components and why might they be added?

Components are individual hazelnut proteins. Some, like Cor a 1, are linked to milder, pollen-related symptoms. Others, like Cor a 9 and Cor a 14, are linked to a higher chance of reactions that affect the whole body. Some labs add these tests automatically when the whole hazelnut result is 0.10 kU/L or higher.

Does a positive hazelnut result mean I should avoid other nuts?

Not automatically. Hazelnut proteins can look like those in other nuts and in peanut, so some people react to more than one, but many do not. Ask your allergist which nuts need testing or a supervised challenge before you cut foods out.

Show the science and sources

For clinicians and researchers

Quantitative IgE to a whole hazelnut extract (Corylus avellana, ImmunoCAP f17). Reported as allergen-specific IgE by ImmunoCAP fluoroenzyme immunoassay in kUA/L, with calibrators traceable to the WHO IgE reference (IRP 75/502). The FDA-reviewed system has a limit of quantitation of 0.1 kUA/L and reports up to 100 kUA/L; its maker recommends a 0.35 kUA/L cutoff and tells each lab to set its own range (FDA review K173726). Components help separate pollen-related from primary allergy (Mayo Clinic Laboratories): Cor a 1 (PR-10, a Bet v 1 homolog) is heat- and digestion-labile, cross-reacts with birch and is mostly linked to local oropharyngeal symptoms; Cor a 8 (a lipid transfer protein) is heat- and digestion-stable and ranges from clinically silent to severe; Cor a 9 (11S globulin) and Cor a 14 (2S albumin) are heat- and digestion-stable and linked to a higher risk of severe systemic reactions. Cor a 9 can cross-react with 11S globulins in walnut, peanut, Brazil nut, soybean, cashew, almond and pistachio. Mayo's reflex test adds the four components when whole hazelnut IgE is 0.10 kU/L or more. Mayo cautions that negative results do not fully exclude a clinical reaction, and that positive results are not diagnostic. Sensitization alone does not define food allergy (NIAID 2010). Nonspecific binding can cause false positives when total IgE exceeds about 2,500 kU/L.

LOINC 6136-6 (primary), 112135-9. Specimen: serum.

Sources

  1. Hazelnut-Food, IgE, Serum (test ID NUTH), Mayo Clinic Laboratories
  2. Hazelnut-Food Components, IgE, Serum (Non-Orderable) (test ID NUTHX), Mayo Clinic Laboratories
  3. Allergen, Food, Hazelnut (Filbert) (ARUP test 0098617), ARUP Laboratories
  4. Hazelnut (Filbert) (F017-IgE Hazelnut) (Labcorp test 602483), Labcorp
  5. ImmunoCAP Specific IgE (allergen component f447) 510(k) decision memorandum K173726, U.S. Food and Drug Administration
  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. Specific IgE antibody criteria for Japanese cedar, Uni-CAP method (Appendix 3, in Japanese), Ministry of the Environment, Japan
  8. Allergy Testing units (LOINC Community Forum thread), Regenstrief Institute, LOINC Community Forum

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

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