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Blood Test Tracker

Brazil Nut IgE

Measures IgE antibodies to Brazil nut to show whether your immune system has become sensitized to it.

AI-verified against cited sources. Awaiting expert reviewAlso called f18, F018LOINC 6050-9

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What it is

This test measures IgE, the antibody type involved in allergic reactions, against Brazil nut (ImmunoCAP f18). Brazil nut is a tree nut that grows in the Amazon region. Results come in kilounits per liter (kU/L), and many labs also print a class from 0 to 6. Some labs automatically add a second test for Ber e 1, the main Brazil nut allergen, when this result is about 0.10 kU/L or higher.

Why it matters

In people who are allergic, Brazil nut can cause reactions from an itchy mouth to anaphylaxis. A positive result alone does not show that you are allergic, because many people have antibodies to nuts they eat without any trouble, and the antibodies can also come from related nuts. The result is most useful alongside your history of reactions.

If it’s high

A level above the 'none detected' range means the lab found IgE antibodies to Brazil nut. This is called sensitization. It is not the same as an allergy, and the number cannot tell you how severe a reaction would be. Higher levels make a reaction more likely, but your history, and sometimes a supervised food challenge, is what shows whether you are allergic. Your clinician can put the result in context.

Common causes

  • Sensitization to Brazil nut with no reaction when it is eaten
  • IgE that cross-reacts with related tree nuts such as walnut, pecan, hazelnut or cashew
  • Brazil nut allergy

What can help

  • Talk with an allergist about what this result means for you, including which nuts are safe to eat
  • Ask whether a Ber e 1 component test or a supervised food challenge would add clarity
  • Ask your clinician before adding nuts to the diet or removing them because of a number

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: ARUP Laboratories, Labcorp, Children's Minnesota Laboratory, Thermo Fisher Scientific (Phadia), American Academy of Pediatrics (Pediatrics).

ImmunoCAP IgE classes (ARUP, Iowa, Children's Minnesota and CUHK; labs differ on which class an exact edge value falls in)

  • 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

Labcorp class scale (cutoffs differ from the ImmunoCAP scale above; exactly 100.00 is class V)

  • Class 0: negativebelow 0.1 kU/L
  • Class 0/I: equivocal or low0.1 to under 0.32 kU/L
  • Class I: low0.32 to under 0.56 kU/L
  • Class II: moderate0.56 to under 1.41 kU/L
  • Class III: high1.41 to under 3.91 kU/L
  • Class IV: very high3.91 to under 19.01 kU/L
  • Class V: very high19.01 to under 100 kU/L
  • Class VI: very high100 and above kU/L

What can affect your result

  • Related tree nuts and seeds, which can cause cross-reacting IgE
  • Eczema, asthma and other allergies, which often occur together with food sensitization
  • The lab and test brand, because results from different systems are not directly comparable
  • Antihistamines generally don't interfere with blood IgE tests, unlike skin tests (AAP). MedlinePlus advises telling your provider about everything you take, since some medicines may matter for this test, so ask your clinician before changing any medicine.
  • Assays from different manufacturers aren't equivalent, so compare results only from the same lab and method (AAP).

Slow. IgE levels usually shift over months to years, not weeks.

When to talk to a clinician

Get urgent medical help for trouble breathing, swelling of the lips, tongue or throat, repeated vomiting, widespread hives, dizziness or fainting after eating nuts. Otherwise, talk with a clinician before eating Brazil nut if you have had any reaction to it, even if this result is low.

Questions you could ask

  • Which lab method was used, and should I use the same lab for future results?
  • Does this result match any reaction I have had to Brazil nut?
  • Would a Ber e 1 test or a supervised food challenge help?
  • Which other nuts do I need to be careful with?
  • Does a low result mean I can eat Brazil nut, or do we need more testing?

Questions people ask

What is the Ber e 1 test my lab added?

Ber e 1 is the main protein in Brazil nut that triggers allergic reactions. Some labs add it automatically when the Brazil nut result is about 0.10 kU/L or higher. It can help show whether the antibodies are to the Brazil nut protein itself or to similar proteins in other nuts.

Does a positive Brazil nut result mean I should avoid all nuts?

Not necessarily. Brazil nut IgE can cross-react with other tree nuts, but being sensitized to a nut is not the same as reacting to it. An allergist can tell you which nuts to avoid based on your history and tests.

What do the class numbers 0 to 6 mean?

The class groups the kU/L number from none detected (class 0) to very high (class 6). Higher classes mean more antibody and a higher chance of a reaction, but not a more severe one. Labcorp's class cutoffs differ from the ones ARUP and many hospital labs use, so compare the kU/L number rather than the class between labs.

Show the science and sources

For clinicians and researchers

Quantitative IgE to a Brazil nut (Bertholletia excelsa) extract (ImmunoCAP f18) by fluoroenzyme immunoassay; ARUP and Labcorp both use the ImmunoCAP system, which reports about 0.1 to 100 kUA/L. Results from the different FDA-cleared IgE systems are not equivalent (AAP 2012). Ber e 1 (f354), a 9 kDa 2S albumin, is the major allergen and resists heat and pepsin digestion; Thermo Fisher notes that Ber e 1 IgE can serve as a better marker of true Brazil nut allergy than the whole extract. Thermo Fisher also lists Ber e 2 (an 11S globulin-like protein) as a major allergen. ARUP (test 3018639) adds Ber e 1 when the Brazil nut result is 0.1 kU/L or higher, and Labcorp (profile 603972) adds it when the result is above 0.10 kU/L. Thermo Fisher reports co-sensitization with walnut, pecan, hazelnut, cashew and macadamia. Higher sIgE reflects the likelihood of a reaction, not its severity, and sensitization is common without clinical allergy (AAP 2012). ARUP reports 0.10 to 0.34 kU/L as 'clinical relevance undetermined'.

LOINC 6050-9 (primary), 112147-4. Specimen: serum.

Sources

  1. Allergen, Food, Brazil Nut With Reflex to Component, IgE (test 3018639), ARUP Laboratories
  2. Brazil Nut (test 602477), Labcorp
  3. Allergen Profile, Brazil Nut, IgE With Component Reflexes (test 603972), Labcorp
  4. Sample report 607120, Allergens with Component Reflexes Area 20 (class description table), Labcorp
  5. Allergen (IgE) ImmunoCAP, University of Iowa Hospitals & Clinics, Pathology Handbook
  6. Allergen IgE (laboratory test information), Children's Minnesota Laboratory
  7. Immunoglobulin E (IgE, Allergen-Specific), Serum, Chinese University of Hong Kong, Prince of Wales Hospital ward manual
  8. Your quick guide to using ImmunoCAP Specific IgE testing, Thermo Fisher Scientific (Phadia) (2024)
  9. Allergy Testing in Childhood: Using Allergen-Specific IgE Tests (clinical report), American Academy of Pediatrics (Pediatrics) (2012)
  10. Allergy Blood Tests, MedlinePlus (National Library of Medicine)
  11. Allergen Encyclopedia: Brazil nut (f18), Thermo Fisher Scientific (Phadia)

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

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