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Blood Test Tracker

Codfish IgE

Shows whether your immune system has made IgE antibodies to codfish. This is called sensitization and doesn't always mean a fish allergy.

AI-verified against cited sources. Awaiting expert reviewAlso called f3, F003LOINC 6082-2

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What it is

Codfish is a common white fish. This test measures IgE, the type of antibody linked to allergic reactions, that your body has made against codfish. The main codfish allergen is a small muscle protein called parvalbumin (Gad c 1). It survives cooking and is very similar in many kinds of fish, so IgE to cod often shows up for other fish too. Sensitization means your body has made IgE antibodies to a substance. It does not always mean you are allergic.

Why it matters

Fish allergy can cause reactions that range from hives and stomach upset to a serious reaction called anaphylaxis. A positive codfish result shows that IgE is present. It does not prove you are allergic, and many sensitized people eat fish without trouble. A negative result also doesn't fully rule out an allergy. Your history of reactions matters most, and an allergy specialist may use a supervised food challenge to settle the question.

If it’s high

A result above your lab's usual range means your body has made IgE antibodies to codfish. It is more likely to match a true fish allergy if you have had symptoms soon after eating fish. The number alone can't tell how strong a reaction would be, and no blood test can predict how severe a future reaction will be.

Common causes

  • Sensitization without symptoms, which is common with food IgE tests
  • Cross-reaction with parvalbumin, the shared protein in many fish, so cod IgE can be positive in people who react to other fish
  • A weak result of 0.10 to 0.34 kU/L, which labs treat as uncertain
  • A true fish allergy, with symptoms soon after eating fish

What can help

  • If you have had symptoms after eating fish, talk with your clinician before eating it again
  • Ask whether an allergy specialist could test other kinds of fish and decide if a supervised food challenge makes sense
  • Ask for a written plan for what to do if you have a reaction

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: 0–0.1 kU/L. Source: Thermo Fisher Scientific, ARUP Laboratories, Labcorp, Quest Diagnostics, Thermo Fisher Scientific (Phadia), Journal of Allergy and Clinical Immunology, NIAID / Journal of Allergy and Clinical Immunology, World Allergy Organization Journal, Clinical Reviews in Allergy & Immunology, Annals of Allergy, Asthma & Immunology, Children's Minnesota.

ImmunoCAP class scale as printed by Quest and ARUP (cut points differ by about 0.01 between labs)

  • Class 0: absent or undetectablebelow 0.1 kU/L
  • Class 0/1: very low level, relevance uncertain0.1 to under 0.35 kU/L
  • Class 1: low level0.35 to under 0.7 kU/L
  • Class 2: moderate level0.7 to under 3.5 kU/L
  • Class 3: high level3.5 to under 17.5 kU/L
  • Class 4: very high level17.5 to under 50 kU/L
  • Class 5: very high level50 to under 100.01 kU/L
  • Class 6: very high level100.01 and above kU/L

Labcorp class scale (ImmunoCAP, as printed on Labcorp reports)

  • 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 100.01 kU/L
  • Class VI: very high100.01 and above kU/L

What can affect your result

  • Species: cod IgE often cross-reacts with other fish, but IgE to another fish doesn't always mean you react to it when you eat it
  • Cooking: the main fish allergen (parvalbumin) is very heat-stable, so cooking doesn't remove it
  • Age and how long you have avoided fish can change how a given number relates to symptoms
  • Lab method: results from different labs or assay systems may not be comparable
  • Medicines: antihistamines do not change this blood test, unlike skin prick testing
  • Very high total IgE can produce weak, nonspecific positive results.
  • Different assay systems give different numbers for the same blood sample, so compare results from the same lab and method.
  • Some labs reject samples that are hemolyzed (red cells broken), jaundiced (icteric) or lipemic (very fatty).

Antibody levels usually change slowly, over months to years.

When to talk to a clinician

Call your local emergency number if, soon after eating fish, you have trouble breathing, throat tightness, swelling of the lips or tongue, repeated vomiting, dizziness or fainting. See a clinician soon if you get hives, itching or stomach upset after eating fish.

Questions you could ask

  • How should I read this result if I've never had a reaction to fish?
  • Does this result fit the symptoms I've had after eating fish?
  • Should I see an allergy specialist, and would testing for other kinds of fish help?
  • Is a supervised food challenge appropriate for me?
  • What should my plan be if I have a reaction?

Questions people ask

If my cod result is positive, do I have to avoid all fish?

Not necessarily. Many fish share the same protein, so IgE to cod often shows up for other fish, but IgE to another fish doesn't always mean you react when you eat it. One review reported that around 4 in 10 people with allergy to this protein tolerate at least one fish species, and fish with less of it, such as tuna, are more often tolerated. An allergy specialist can test and, if it makes sense, supervise safe trials. Avoid trying fish on your own if you have had a reaction.

Can I have a negative result and still be allergic?

It's uncommon, but yes. Undetectable IgE can happen in people with an IgE-mediated food allergy. If your history strongly suggests a reaction, your clinician may suggest a supervised food challenge before you eat fish again.

Can I test positive without ever having a reaction?

Yes. IgE sensitization is common and doesn't always cause symptoms. A food IgE test on its own doesn't confirm a food allergy.

Show the science and sources

Units

  • 1 kU/L = 1 kU/L
  • 1 kU/L = 1 UA/mL

For clinicians and researchers

ImmunoCAP f3 is a fluorescent enzyme immunoassay for IgE to a codfish extract (manufacturer range 0.1 to 100 kUA/L; above 100 is printed as >100). The dominant allergen, Gad c 1, is a beta-parvalbumin (a panallergen across fish species) that is extremely heat-stable. Enolase and aldolase are other, heat-labile fish allergens, and fish with less beta-parvalbumin, such as tuna (under 0.05 mg/g, versus 1 to 2.5 mg/g in cod, in one survey), are sometimes tolerated by people who react to other species. One review reported that about 41% of people with allergy to beta-parvalbumin tolerate at least one fish species. In the NIAID 2010 summary table, codfish versus other fish showed IgE cross-reactivity in 5% to 100% and clinical reactivity in 30% to 75% of studied patients, so serologic cross-reactivity does not equal clinical cross-reactivity. Gad c 1 component testing is listed as a separate marker in this catalog. Undetectable IgE occasionally occurs in IgE-mediated food allergy, which is why a supervised oral food challenge remains the reference standard. ARUP labels 0.10 to 0.34 kU/L as clinical relevance undetermined, while other labs call it equivocal or very low. The class tables differ slightly between labs, so use the class your own report prints.

LOINC 6082-2 (primary), 112163-1. Specimen: serum.

Sources

  1. Allergens, Food, Fish Profile IgE (test 2007036), ARUP Laboratories
  2. F003-IgE Codfish (test 602465), Labcorp
  3. Sample patient report: Allergens with Component Reflex, Area 20 (test 607120), Labcorp (2021)
  4. ImmunoCAP Specific IgE Blood Test: Allergy Test List (interpretation table and test codes), Quest Diagnostics (2017)
  5. ImmunoCAP Specific IgE blood test results: Interpretation (respiratory results interpretation guide), Thermo Fisher Scientific (Phadia) (2023)
  6. ImmunoCAP Fish, Shellfish and Mollusk Allergens (Thermo Fisher product page; lists f3 codfish; measuring range 0.1 to 100 kUA/L), Thermo Fisher Scientific
  7. ImmunoCAP allergy: Change to Reference Interval Interpretation, UR Medicine Labs, University of Rochester Medical Center (2022)
  8. Prevalence of allergic sensitization in the United States: results from the National Health and Nutrition Examination Survey (NHANES) 2005-2006, Journal of Allergy and Clinical Immunology (2014)
  9. Guidelines for the Diagnosis and Management of Food Allergy in the United States: Report of the NIAID-Sponsored Expert Panel, NIAID / Journal of Allergy and Clinical Immunology (2010)
  10. IgE allergy diagnostics and other relevant tests in allergy, a World Allergy Organization position paper, World Allergy Organization Journal (2020)
  11. Fish Allergy: Fishing for Novel Diagnostic and Therapeutic Options, Clinical Reviews in Allergy & Immunology (2022)
  12. Codfish allergy in adults: IgE cross-reactivity among fish species, Annals of Allergy, Asthma & Immunology (1997)
  13. Allergen IgE (laboratory test manual entry; class table and reporting rules), Children's Minnesota (2018)

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

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