Biomarker: F427-IgE Ara h 9

Overview

F427-IgE Ara h 9 measures serum specific immunoglobulin E (sIgE) antibodies directed against Ara h 9, a peanut allergen belonging to the nonspecific lipid transfer protein family. Ara h 9 is heat- and digestion-resistant and may cross-react with related lipid transfer proteins, including peach Pru p 3 and mugwort Art v 3. A positive result indicates sensitization, but does not by itself establish clinical peanut allergy or predict reaction severity. The test may support evaluation of suspected peanut or lipid transfer protein allergy, particularly in Mediterranean populations or when testing with whole-peanut extract is negative, although its sensitivity is limited.

Clinical Use Cases

Supports component-resolved evaluation of suspected peanut allergy.
Identifies sensitization to the peanut lipid transfer protein Ara h 9.
Helps assess possible lipid transfer protein cross-reactivity involving peanut, peach, and other plant foods.
May be useful when clinical symptoms suggest peanut allergy but whole-peanut extract sIgE is negative.
Provides additional information in selected patients with suspected lipid transfer protein allergy.
May help distinguish a lipid transfer protein sensitization pattern from pollen-associated Ara h 8 sensitization.
Should be interpreted with clinical history and, when indicated, supervised oral food challenge because a positive result does not confirm clinical reactivity.

Specimen Types

Venous blood, processed to obtain serum.
Serum is the typical specimen for quantitative Ara h 9-specific IgE measurement.

Measurement Methods

Singleplex serum allergen-specific IgE immunoassay using purified or recombinant Ara h 9.
Component-resolved diagnostics performed as an individual assay.
Multiplex allergen microarray testing that includes Ara h 9, usually providing semiquantitative results.
Results are commonly reported in kUA/L or kU/L, depending on the assay system.

Test Preparation and Influencing Factors

Fasting is generally not required for serum-specific IgE testing.
Antihistamines usually do not affect serum sIgE results, although they can affect skin-prick testing.
Recent peanut ingestion does not generally require postponing blood collection.
Results may vary with age, geographic region, dietary exposures, and the patient’s overall sensitization pattern.
Cross-reactivity with lipid transfer proteins from peach, mugwort, plane tree, and other plants can produce a positive result without clinically relevant peanut allergy.
A positive result demonstrates sensitization rather than definite allergy; symptom history and, when necessary, supervised oral food challenge remain important for diagnosis.
Ara h 9-specific IgE has relatively low sensitivity, so a negative result does not reliably exclude peanut allergy.