Biomarker: F048-IgE Onion

Overview

F048-IgE Onion measures immunoglobulin E (IgE) antibodies that recognize onion (Allium cepa) allergens, usually in serum. IgE is involved in immediate allergic reactions, and onion-specific IgE indicates sensitization to onion. High levels may support an IgE-mediated onion allergy when consistent symptoms occur after exposure, while low or undetectable levels make sensitization less likely but do not independently exclude allergy. The test is clinically useful as part of an allergy evaluation, but a positive result alone does not confirm clinical allergy or predict reaction severity.

Clinical Use Cases

Supports evaluation of suspected immediate allergic reactions after eating, handling, or inhaling onion.
Helps identify onion sensitization in patients with a compatible history of urticaria, angioedema, respiratory symptoms, gastrointestinal symptoms, or anaphylaxis.
May be used alongside skin-prick testing and clinical history when evaluating suspected IgE-mediated food allergy.
Supports investigation of suspected cross-sensitization involving garlic and other Allium species.
May help guide a medically supervised oral food challenge when the history and initial testing are inconclusive. Oral food challenge remains the reference method for confirming food allergy.

Specimen Types

Serum, typically collected by venipuncture for quantitative allergen-specific IgE testing.
Skin-prick test material, using an onion extract, for in-vivo assessment of sensitization.
In selected research or specialized clinical settings, whole blood may be used for cellular assays such as basophil activation testing, although this is not the usual specimen for routine onion-specific IgE measurement.

Measurement Methods

Fluorescence enzyme immunoassay or related automated immunoassay for quantitative serum onion-specific IgE.
ImmunoCAP testing, an automated allergen-specific IgE immunoassay used in clinical studies of onion allergy.
Radioallergosorbent testing, an older serum-specific IgE method used in onion sensitization research.
Enzyme-linked immunosorbent assay, including inhibition assays for investigating allergen binding or possible cross-reactivity in research settings.
Skin-prick testing with onion extract as a complementary in-vivo method, although it does not measure serum IgE concentration.

Test Preparation and Influencing Factors

Fasting is generally not required for an allergy blood test.
Patients should report all medicines and supplements to the ordering clinician. Medication instructions vary by test type; antihistamines can interfere with skin-prick testing, while blood-test requirements may differ by laboratory.
Medications should not be stopped unless specifically instructed by a health care professional.
Testing should be directed by a relevant clinical history rather than broad, unspecific food panels, which can produce clinically irrelevant positive results.
A positive result indicates sensitization and must be interpreted with the timing, type, and reproducibility of symptoms after onion exposure.
The measured IgE concentration does not reliably predict reaction severity.
Results may vary with the onion extract, assay platform, calibration, and laboratory reference classification.
Recent ingestion of onion is not generally required for serum-specific IgE testing, but the collection date and recent allergic reactions should be documented.
A negative result reduces the likelihood of IgE sensitization but does not absolutely exclude clinically relevant allergy.