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Blood Test Tracker

Pecan Nut IgE

Measures IgE antibodies to pecan nut in your blood. A detectable result means you are sensitized to pecan, which is not the same as an allergy.

AI-verified against cited sources. Awaiting expert reviewAlso called f201LOINC 6208-3

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What it is

IgE is a type of antibody your immune system can make against a food protein. Pecan is a tree nut in the walnut family. This test measures IgE to an extract of pecan nut using a method called ImmunoCAP (also written f201). It is a food test, and it is separate from the pecan tree pollen test. Results come in kilounits per liter (kU/L), and many labs also print a class from 0 to 6.

Why it matters

Tree nut allergy is less likely than milk or egg allergy to be outgrown. In US surveys from 2015 to 2016, about 0.6% of children and 0.5% of adults reported a pecan allergy. This test can help you and your clinician look at whether pecan might be behind symptoms such as hives, stomach upset or mouth itching. On its own it cannot confirm an allergy, because many people with pecan IgE eat pecans without trouble. Pecan is closely related to walnut. In studies of people with tree nut allergy, nearly all of those allergic to pecan were also allergic to walnut. Roughly two in three of those allergic to walnut were also allergic to pecan. 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 pecan. In general, higher levels make a reaction to pecan more likely, but the link is not exact. Some people with high levels eat pecans with no problem, and some people with low or even undetectable levels do react. Your clinician reads the number together with your symptoms.

Common causes

  • Sensitization without symptoms, where you make the antibody but eat pecans with no problem
  • Cross-reacting IgE from walnut, whose proteins are very similar to pecan's
  • Cross-reacting IgE from other tree nuts or peanut
  • Pollen allergy, since some nut proteins resemble pollen proteins, which usually causes milder mouth symptoms
  • A true pecan 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 of eating pecans and other tree nuts
  • Keep notes on any symptoms after pecans or foods that contain them, including how soon they began
  • Ask whether a walnut test, a skin test or a supervised food challenge would help clarify your result
  • If you have been told to avoid pecans, 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, Allergy, Allergy, Asthma & Immunology Research, 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

What can affect your result

  • Age, and how long pecan has been avoided or eaten before the test
  • Walnut allergy, since the two nuts are close relatives and often go together
  • Other allergies, such as to other tree nuts, peanut or pollen, 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, because results from different systems are not directly comparable
  • 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.
  • 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 pecans 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

  • Could my pollen allergy be part of this result?
  • How often, if at all, should we recheck this?
  • Does this result fit with my history of eating pecans?
  • Would a walnut test, a skin test or a supervised food challenge help clarify what this result means?
  • Should I be checked for reactions to other tree nuts or peanut?
  • My result is in the usual range but I have had symptoms after pecans. What should we do next?

Questions people ask

Does a positive pecan IgE mean I am allergic to pecans?

Not by itself. The test shows that your immune system has made IgE to pecan, which is called sensitization. An expert panel convened by the NIAID says these blood tests alone cannot confirm a food allergy. In one US study of people with a positive tree nut test, about a third (36%) had a history of reactions to tree nuts. Your clinician looks at the result with your symptoms, and sometimes a supervised food challenge.

I am allergic to walnut. Should I expect to react to pecan?

Often, but not always. Pecan and walnut are close relatives. In studies, roughly two in three people allergic to walnut were also allergic to pecan, and nearly everyone allergic to pecan was also allergic to walnut. Ask your clinician whether you should avoid pecans and how to find out for sure.

If my result is negative, can I rule out a pecan allergy?

Not always. A negative result makes an IgE-mediated allergy less likely, but undetectable levels do sometimes occur in people who react. If you have had symptoms after eating pecans, tell your clinician even when this result is negative.

Show the science and sources

For clinicians and researchers

Quantitative allergen-specific IgE to a pecan nut extract (Carya illinoinensis, ImmunoCAP f201) by fluoroenzyme immunoassay. Mayo and ARUP (as a component of its tree nut profile) list LOINC 6208-3. The ImmunoCAP Specific IgE system reports up to 100 kUA/L with a limit of quantitation of 0.1 kUA/L, and its maker recommends a 0.35 kUA/L cutoff while telling each lab to set its own range (FDA review K173726). Mayo flags class 2 and above (0.70 kU/L or more), while ARUP lists 0.34 kU/L or lower as the pecan reference interval. Allergen-specific IgE shows sensitization, not clinical allergy; higher levels go with a higher probability of reaction, but predictive values vary by population and cannot be moved between assay systems, and undetectable IgE occasionally occurs in IgE-mediated food allergy (NIAID 2010, Guideline 7). NIAID's cross-reactivity table lists about 92% sensitization between tree nuts with 12 to 37% clinical reactivity (from reported reactions, not challenges), and notes higher serum IgE correlations between pecan and walnut. In the NUT CRACKER study of 83 patients evaluated for six tree nuts, most were sensitized to 5 or 6 nuts but over half were allergic to only 1 or 2; two thirds of walnut-allergic patients were also allergic to pecan, all pecan-allergic patients were allergic to walnut, and knowledge of which nuts tend to go together, combined with skin tests and a basophil activation test, separated allergic from tolerant patients correctly for pecan in 66%, the lowest of the four nuts reported (Elizur 2018). A 2025 review reports that 97 to 100% of people allergic to pecan are also allergic to walnut and 64 to 75% of walnut-allergic people are allergic to pecan, one of the two highest overlaps along with cashew and pistachio, and that storage proteins and lipid transfer proteins go with systemic reactions while PR-10 proteins and profilins usually cause milder pollen-food symptoms (Jeong 2025). In one US series of 278 patients with positive tree nut IgE, 36% had a history of acute reactions, and 58% of those challenged who had all IgE levels of 5 kUA/L or less passed, though NIAID noted an ideal cutoff cannot be set from those data. Mayo notes false positives can occur above about 2,500 kU/L total IgE.

LOINC 6208-3 (primary), 112234-0. Specimen: serum.

Sources

  1. Pecan-Food, IgE, Serum (test ID PEC), Mayo Clinic Laboratories
  2. Allergens, Food, Tree Nuts Profile IgE (ARUP test 3017913), ARUP Laboratories
  3. 510(k) Decision Memorandum K173726: ImmunoCAP Specific IgE (ImmunoCAP Allergen f447, rAra h 6, Peanut), U.S. Food and Drug Administration (2018)
  4. 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)
  5. Allergy Blood Test, MedlinePlus, National Library of Medicine
  6. NUT Co Reactivity - ACquiring Knowledge for Elimination Recommendations (NUT CRACKER) study, Allergy (2018)
  7. Update on Tree Nut and Seed Allergies: Prevalence, Clinical Characteristics, Diagnosis, and Management, Allergy, Asthma & Immunology Research (2025)

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

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