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Blood Test Tracker

Alpha-gal IgE

Measures IgE antibodies to alpha-gal, a sugar found in red meat and other mammal products. It is linked to a tick-related allergy that causes delayed reactions.

AI-verified against cited sources. Awaiting expert reviewAlso called o215, α-GalLOINC 73837-7

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What it is

Alpha-gal is a sugar found in most mammals, such as cows and pigs, but not in people. In the US, bites from the lone star tick are most often linked to making IgE antibodies against it, according to the CDC. This test measures that IgE in your blood. In alpha-gal syndrome, reactions to red meat, and sometimes dairy or gelatin, often start hours after eating rather than minutes.

Why it matters

Alpha-gal reactions can be hard to link to a meal because they usually begin 2 to 6 hours later. The IgE blood test is the main test clinicians use, along with your symptoms and history. But many people have alpha-gal IgE and no symptoms, especially where lone star ticks live, so the number alone cannot tell whether you have the syndrome. In one German study of hunters and forest workers, about 1 in 5 had alpha-gal IgE, but only 5 of the 58 who tested positive had allergic symptoms.

If it’s high

A level above your lab's range means your immune system has made IgE against alpha-gal. For some people this goes along with allergic reactions to red meat, dairy or gelatin that start hours after eating. Many people with a positive result have never had a reaction. How strongly people react varies a lot, so the number alone cannot say how severe a reaction might be.

Common causes

  • Sensitization without symptoms, which is common in areas with many ticks
  • Tick bites, most often from the lone star tick in the US (other tick species elsewhere)
  • Alpha-gal syndrome, a tick-related allergy to red meat and other mammal products
  • 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 or your clinician about your result and your symptom history, especially any hives, stomach pain or swelling that began hours after eating red meat, dairy or gelatin
  • Ask which foods and products that contain mammal ingredients, such as gelatin, matter for you
  • Preventing tick bites is the main way to limit new exposure, and the CDC has practical advice

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, Labcorp, Centers for Disease Control and Prevention, Journal of Allergy and Clinical Immunology, 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

What can affect your result

  • Ongoing tick bites can keep levels up, while levels tend to fall in people who avoid further bites
  • Where you live: the lone star tick has long been common in the southern and southeastern US and has spread into the central Midwest and up the eastern coast (Mayo Clinic Laboratories)
  • 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
  • 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).
  • Different labs and test brands give different numbers for the same blood sample, so compare results from the same lab and system.

Slow. Levels tend to fall over time in people who avoid further tick bites, but not in people who keep getting bitten. No fixed timeline is given in the sources.

When to talk to a clinician

Get emergency care right away (call 911 or your local emergency number) for trouble breathing, swelling of the lips, tongue or throat, dizziness or fainting, or severe stomach pain with vomiting, even if it starts hours after a meal. If you have hives, stomach upset or other symptoms several hours after eating red meat, dairy or gelatin, tell your clinician, even if your result is in the usual range.

Questions you could ask

  • How can I lower my chance of more tick bites?
  • Should we recheck this over time?
  • Do my symptoms and tick-bite history fit with this result?
  • Which foods and products with mammal ingredients, such as gelatin or dairy, should I ask about?
  • Would a skin test or other testing help clarify my result?
  • My result is in the usual range but I have had delayed reactions after red meat. What should we do next?

Questions people ask

I tested positive for alpha-gal IgE. Do I have alpha-gal syndrome?

Not necessarily. The CDC says a positive alpha-gal IgE test does not mean a person has the syndrome, and positive results can occur in people with no symptoms, particularly in regions with lone star ticks. Clinicians look at the result together with your symptoms, whether reactions are delayed, and your history of tick bites or time outdoors.

Why do reactions start hours after eating?

Alpha-gal reactions usually start about 2 to 6 hours after eating red meat or dairy, according to the CDC, unlike most food allergies, which start within minutes. Experts are still studying why the delay happens.

Will my level change over time?

It can. Studies described in a 2020 NIAID workshop report found that alpha-gal IgE levels tend to fall in people who avoid further tick bites, but not in people who keep being bitten.

Show the science and sources

For clinicians and researchers

Quantitative IgE to galactose-alpha-1,3-galactose (ImmunoCAP o215) by fluoroenzyme immunoassay; ARUP and Labcorp use ImmunoCAP and Mayo lists FEIA. Assays use alpha-gal-bearing proteins on the solid phase, most often beef thyroglobulin or cetuximab, with similar performance (NIAID workshop 2020). Reports of reaction onset range from about 2 to 8 hours after ingestion (CDC 2 to 6 hours, Mayo 3 to 6 hours, Labcorp 3 to 8 hours), and the NIAID workshop lists exercise, alcohol and NSAIDs as cofactors. Sensitization is common without symptoms: among 300 hunters and forest workers in southwest Germany, 19.3% had alpha-gal IgE, and 5 of the 58 positives (cutoff 0.35 IU/mL) had symptoms, and the workshop notes sensitization can reach 10 to 20% of people in some regions where ticks are common. The CDC states a positive sIgE test does not mean a person has AGS, and skin testing may also be used. IgE to alpha-gal is also linked to immediate reactions to intravenous cetuximab (Mayo). Labcorp notes total IgE can help the assessment because some cases are non-atopic with low total IgE. Mayo flags class 2 and above (0.70 kU/L or more) and notes false positives can occur above about 2,500 kU/L total IgE.

LOINC 73837-7 (primary). Specimen: serum.

Sources

  1. Galactose-Alpha-1,3-Galactose (Alpha-Gal), IgE, Serum (test ID ALGAL), Mayo Clinic Laboratories
  2. Allergen, Food, Alpha-Gal (galactose-alpha-1,3-galatose) IgE (ARUP test 3003923), ARUP Laboratories
  3. Galactose-Alpha-1,3-Galactose (Alpha-Gal), IgE, Serum (Labcorp test 650001), Labcorp
  4. About Alpha-gal Syndrome, Centers for Disease Control and Prevention (2026)
  5. Clinical Diagnosis and Testing (Alpha-gal Syndrome), Centers for Disease Control and Prevention (2026)
  6. Symptoms of Alpha-gal Syndrome, Centers for Disease Control and Prevention (2026)
  7. On the cause and consequences of IgE to galactose-alpha-1,3-galactose: A report from the National Institute of Allergy and Infectious Diseases Workshop on Understanding IgE-Mediated Mammalian Meat Allergy, Journal of Allergy and Clinical Immunology (2020)
  8. 510(k) Decision Memorandum K173726: ImmunoCAP Specific IgE (ImmunoCAP Allergen f447, rAra h 6, Peanut), U.S. Food and Drug Administration (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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