Biomarker: O215-IgE Alpha-Gal

Overview

O215-IgE Alpha-Gal measures immunoglobulin E antibodies directed against galactose-alpha-1,3-galactose, a carbohydrate found on many non-primate mammalian cells and products. These antibodies are associated with alpha-gal syndrome, an allergy that can cause delayed reactions after exposure to mammalian meat or other mammalian-derived products. A detectable result indicates sensitization but does not by itself establish clinical allergy, because some people have alpha-gal-specific IgE without symptoms. The test is clinically useful when interpreted with compatible symptoms, exposure history, and timing of reactions.

Clinical Use Cases

Support diagnosis of alpha-gal syndrome in patients with compatible delayed allergic reactions after mammalian meat or other mammalian-derived exposures.
Identify sensitization to alpha-gal in patients with a relevant history of tick exposure or suspected tick-associated allergy.
Provide laboratory confirmation for clinical and public-health case definitions of alpha-gal syndrome. A serum or plasma concentration of at least 0.1 kU/L or IU/mL is used as confirmatory laboratory evidence in the CDC case definition.
Monitor alpha-gal-specific IgE over time in selected patients, particularly after avoidance of additional tick bites. Levels may decline, although the rate varies among individuals.
Support evaluation of suspected mammalian meat allergy when skin-prick testing with meat extracts is inconclusive.

Specimen Types

Serum.
Plasma, including EDTA plasma, when validated by the testing laboratory.

Measurement Methods

Quantitative allergen-specific IgE immunoassay using an alpha-gal allergen component, commonly designated ImmunoCAP Allergen o215.
Automated fluorescence enzyme immunoassay, such as the ImmunoCAP system, with results commonly reported in kU/L or IU/mL.
Allergy skin testing may be used as an adjunct, but blood measurement of alpha-gal-specific IgE is the principal laboratory method for evaluating suspected alpha-gal syndrome.

Test Preparation and Influencing Factors

Fasting is generally not required for alpha-gal-specific IgE blood testing.
Results must be interpreted with symptoms, reaction timing, dietary or medication exposures, and tick-bite or outdoor-exposure history. A positive result alone does not diagnose alpha-gal syndrome.
Additional tick bites may increase alpha-gal-specific IgE levels, whereas sustained avoidance of tick bites may be followed by a decline.
The concentration does not reliably predict reaction severity.
The timing of symptoms is relevant because reactions to alpha-gal commonly occur several hours after exposure rather than immediately.
Antihistamines generally do not interfere with a blood-based specific-IgE assay, although they can affect skin-prick test results.
Total IgE concentration and geographic exposure to ticks may influence interpretation because asymptomatic sensitization is relatively common in some regions.
Testing should be ordered for patients with a compatible clinical history rather than used as a screening test in asymptomatic individuals.