Biomarker: F256-IgE Walnut

Overview

F256-IgE Walnut measures immunoglobulin E (IgE) antibodies directed against walnut proteins in serum. IgE is involved in immediate-type allergic reactions, including reactions that may cause hives, gastrointestinal symptoms, breathing difficulty, or anaphylaxis. A detectable or elevated result indicates sensitization to walnut but does not by itself confirm clinical walnut allergy or predict reaction severity. The test is clinically useful when interpreted with exposure history, symptoms, examination, and, when necessary, skin testing or a medically supervised oral food challenge.

Clinical Use Cases

Evaluation of suspected IgE-mediated walnut allergy.
Assessment of patients with symptoms occurring minutes to hours after walnut exposure.
Support for diagnostic evaluation when skin testing is unsuitable or may be affected by medications or skin disease.
Investigation of possible sensitization to walnut in patients with tree-nut allergy.
Follow-up assessment when an allergist is evaluating whether walnut allergy may have resolved.
Research assessment of walnut sensitization and comparison with component-specific testing, such as Jug r 1-specific IgE.

Specimen Types

Serum from venous blood.
Plasma may be accepted by some laboratory platforms, according to the laboratory’s validated collection requirements.

Measurement Methods

In-vitro allergen-specific IgE immunoassay.
Fluorescence enzyme immunoassay or other solid-phase immunoassay platforms.
Quantitative reporting is commonly expressed in kUA/L or an equivalent IgE concentration unit.
Component-resolved diagnostics may separately measure IgE to walnut proteins, including Jug r 1, Jug r 3, and other recognized walnut components. These are distinct from whole-walnut F256-IgE testing.

Test Preparation and Influencing Factors

Fasting is generally not required for a serum-specific IgE blood test.
Patients should report all medications and supplements. Antihistamines commonly affect skin-prick testing but generally do not interfere with serum-specific IgE measurement.
Do not stop prescribed medication unless instructed by a healthcare professional.
Results should be interpreted with the timing and nature of symptoms, the amount and form of walnut consumed, and the patient’s clinical history.
Cross-reactivity with related tree nuts, pollens, or other plant allergens may produce a positive result without clinical walnut allergy.
A positive result indicates sensitization and does not confirm allergy; a negative or low result also does not completely exclude allergy when the clinical history is strongly suggestive.
The IgE concentration does not reliably predict the severity of a future reaction.
Oral food challenges, when needed, must be performed under specialist medical supervision because walnut can cause severe reactions.