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Blood Test Tracker

Walnut IgE

Measures IgE antibodies to walnut. A raised result can reflect a true walnut allergy or a pollen-related pattern, and it does not confirm an allergy on its own.

AI-verified against cited sources. Awaiting expert reviewAlso called f256LOINC 6273-7

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What it is

This test measures IgE antibodies to walnut (Juglans species, ImmunoCAP f256). Walnut allergy comes in more than one form. Some people react to walnut proteins that survive cooking and digestion, which can cause more serious reactions. Others, especially adults with pollen allergy, mainly get an itchy mouth and throat. This test looks at walnut as a whole, so it cannot tell the forms apart on its own.

Why it matters

Knowing why you are sensitized to walnut matters, because the chance of a serious reaction differs between patterns. That is why some labs add tests for individual walnut proteins (components) when this result is 0.10 kU/L or higher. Walnut and pecan come from the same plant family and share proteins, so many physicians advise treating them together. Your result is read with your history of reactions and sometimes a supervised food challenge. A positive 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 walnut. It shows sensitization. Whether it comes from a true walnut allergy or from a milder pollen-related pattern cannot be told from this number alone.

Common causes

  • A milder pollen-related pattern, such as an itchy mouth and throat, in people with birch pollen allergy
  • A true walnut allergy, including reactions that affect the whole body
  • IgE that also reacts with pecan or other nuts and seeds that share similar proteins
  • Sensitization without any symptoms

What can help

  • Ask an allergist whether tests for walnut components (such as Jug r 1, Jug r 2 and Jug r 3) would help show which pattern you have
  • Ask what to do about walnut, pecan 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 walnut result could be related to it
  • If you have ever reacted to walnut, ask about a plan for accidental exposure

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 (catalog mirrored at testcatalog.org), ARUP Laboratories, U.S. Food and Drug Administration.

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

ImmunoCAP IgE classes (ARUP Laboratories)

  • Class 0: no significant level foundbelow 0.1 kU/L
  • Class 0/1: clinical relevance undetermined0.1 to under 0.35 kU/L
  • Class 1: low0.35 to under 0.71 kU/L
  • Class 2: moderate0.71 to under 3.51 kU/L
  • Class 3: high3.51 to under 17.51 kU/L
  • Class 4: very high17.51 to under 50.01 kU/L
  • Class 5: very high50.01 to under 100.01 kU/L
  • Class 6: very high100.01 and above kU/L

What can affect your result

  • Birch pollen allergy and other pollen allergies, which can cause IgE to walnut
  • Cross-reactivity with pecan (same plant family), hazelnut and other nuts that have similar proteins
  • Which walnut proteins your IgE targets, which this whole-walnut test cannot show
  • 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)
  • 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 walnut 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 walnut is also worth mentioning to your clinician.

Questions you could ask

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

Questions people ask

Does a positive walnut result mean I am allergic to walnut?

Not by itself. The test shows IgE, called sensitization. Some people with walnut IgE eat walnut without trouble, and a negative result does not fully rule out a reaction. Allergists combine your history with the result and sometimes use a supervised food challenge.

What are Jug r 1, Jug r 2 and Jug r 3, and why might they be added?

They are individual walnut proteins. Studies link IgE to Jug r 1 and Jug r 2 with a higher chance of reactions that go beyond the mouth, and IgE to Jug r 3 with both mouth symptoms and body-wide reactions. Some labs, such as Mayo Clinic Laboratories, automatically add the Jug r 1 and Jug r 3 tests when the whole walnut result is 0.10 kU/L or higher.

Do I need to avoid pecans too?

Not automatically. Walnut and pecan share proteins, and many physicians advise avoiding both, but not everyone who reacts to one reacts to the other. 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 walnut extract (Juglans spp., ImmunoCAP f256). Mayo Clinic Laboratories (BLWRF) and ARUP (0055209) both report it with LOINC 6273-7. Reported as allergen-specific IgE by ImmunoCAP fluoroenzyme immunoassay in kUA/L, with calibrators traceable to the WHO IgE reference (IRP 75/502 or the 3rd International Standard 11/234). 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). Mayo's reflex test starts with whole-walnut IgE and adds the walnut components Jug r 1 and Jug r 3 when the result is 0.10 kU/L or higher; it is listed as useful for evaluating suspected walnut food allergy. Thermo Fisher describes Jug r 1 (a 2S albumin seed storage protein), Jug r 2 (a vicilin), Jug r 3 (a nonspecific lipid transfer protein), Jug r 4 (an 11S globulin), Jug r 6 and Jug r 7 (a profilin). It reports that walnut has heat- and digestion-stable proteins linked to a high risk of systemic reactions, that IgE to Jug r 1 and Jug r 2 is associated with risk for systemic reactions, and that Jug r 3 is a stable lipid transfer protein linked to local symptoms and systemic reactions. Walnut and pecan are in the same plant family (Juglandaceae) and share cross-reactive allergens. Cross-reactivity with birch pollen is described through Bet v 1 and Bet v 2, and IgE cross-reactivity has also been reported with pistachio, hazelnut, Brazil nut, chestnut and pine nut. In adults, pollen-associated oral allergy syndrome is the most usual manifestation (Thermo Fisher). Sensitization alone is not sufficient to define food allergy, and sIgE tests alone are not diagnostic; results from different laboratories or assay systems may not be comparable (NIAID 2010).

LOINC 6273-7 (primary). Specimen: serum.

Sources

  1. Walnut-Food, IgE, with Reflex to Walnut-Food Components, IgE, Serum (test ID BLWRF), Mayo Clinic Laboratories (catalog mirrored at testcatalog.org)
  2. Allergen, Food, Walnut (Juglans spp.) IgE (ARUP test 0055209), ARUP Laboratories
  3. f256 Walnut (Allergen Encyclopedia), Thermo Fisher Scientific (Phadia)
  4. ImmunoCAP Specific IgE (allergen component f447) 510(k) decision memorandum K173726, U.S. Food and Drug Administration
  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. Walnut (test 602530), Labcorp

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

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