Biomarker: F423-IgE Ara h 2

Overview

Ara h 2 is a major allergenic protein from peanut (Arachis hypogaea). It is a conglutin-type 2S albumin seed-storage protein and belongs to the peanut allergen family recognized by the WHO/IUIS allergen nomenclature system. Sensitization to Ara h 2 is associated with IgE-mediated peanut allergy, but a positive result indicates allergen-specific sensitization and does not by itself establish clinical allergy. Serum Ara h 2-specific IgE testing can support evaluation of suspected peanut allergy, particularly when interpreted with the clinical history, whole-peanut testing, and, when necessary, a medically supervised oral food challenge.

Clinical Use Cases

Evaluation of suspected peanut allergy: Measures Ara h 2-specific IgE as a component of the diagnostic evaluation in patients with symptoms suggestive of IgE-mediated reactions to peanut.
Serum-specific IgE assessment: Helps determine whether IgE sensitization is directed toward a major peanut component rather than only toward the whole-peanut extract.
Clarification of uncertain cases: May improve diagnostic confidence and help reduce the need for oral food challenges in selected patients, although it cannot replace a challenge when the diagnosis remains unclear.
Interpretation with clinical history: Results should be assessed alongside the timing, reproducibility, and characteristics of symptoms after peanut exposure. Detectable Ara h 2-specific IgE without a compatible clinical history is not sufficient to diagnose peanut allergy.
Assessment alongside other tests: May be used with whole-peanut serum-specific IgE, skin-prick testing, and other peanut components such as Ara h 1, Ara h 3, and Ara h 6.
Clinical risk assessment: Higher Ara h 2-specific IgE concentrations have been associated with reactions during oral food challenges in some studies, but individual variation is substantial and the result should not be used alone to predict reaction severity.

Specimen Types

Serum: The standard specimen for laboratory measurement of Ara h 2-specific IgE.
Blood: Venous blood collection is used to obtain serum for allergen-specific IgE testing.

Measurement Methods

Allergen-specific IgE testing: In-vitro immunoassays measure IgE antibodies directed against Ara h 2 in serum or blood. Results are commonly reported in kUA/L or an equivalent allergen-specific IgE unit.
Component-resolved diagnostics: Measures IgE to the individual peanut protein Ara h 2 rather than only to a whole-peanut extract. This may help distinguish sensitization patterns and provide additional diagnostic information.
Multiplex component testing: Ara h 2 may be measured together with other peanut components, including Ara h 1, Ara h 3, Ara h 6, Ara h 8, and Ara h 9, when broader component profiling is clinically indicated.
Skin-prick testing and oral food challenge: These are clinical evaluation methods rather than blood-based measurements. Skin-prick testing can support assessment of IgE sensitization, while a medically supervised oral food challenge remains the reference method when clinical allergy cannot be confirmed or excluded by history and IgE testing.

Test Preparation and Influencing Factors

Fasting: Fasting is generally not required for serum-specific IgE testing unless other tests collected during the same visit require it.
Medications: Antihistamines can interfere with skin-prick testing but generally do not prevent measurement of serum-specific IgE. Medication decisions should follow the clinician’s instructions.
Clinical history: The timing, reproducibility, and symptoms associated with peanut exposure primarily affect interpretation rather than the laboratory measurement itself.
Sensitization versus allergy: A positive Ara h 2-specific IgE result demonstrates sensitization. Clinical allergy requires correlation with a compatible reaction history or, when appropriate, a medically supervised oral food challenge.
Concentration threshold: Diagnostic cutoffs vary by age, geographic region, assay, and study population. Published thresholds should not be applied universally without clinical validation.
Total IgE and assay characteristics: Total IgE concentration, assay calibration, reporting units, and laboratory-specific analytical characteristics can influence interpretation of quantitative results.
Age and population: Predictive values differ between children and adults and among populations with different peanut exposure patterns and prevalence of peanut allergy.
Cross-reactive sensitization: IgE binding to related proteins can contribute to a positive result without proving that peanut ingestion causes symptoms.
Timing after exposure: Serum-specific IgE generally reflects sensitization over time and does not by itself determine whether a reaction will occur during a particular exposure.
Reaction severity: Ara h 2-specific IgE concentration should not be used alone to predict the severity of a future reaction. Studies have reported associations with challenge outcomes, but substantial individual variation remains.

Cross-Reactivity

Ara h 6 and Ara h 7: These peanut allergens are also conglutin-type 2S albumins. Ara h 2 shares structural and sequence relationships with Ara h 6 and Ara h 7, and IgE responses to these components may overlap.
Other peanut components: Sensitization to Ara h 2 may occur with sensitization to Ara h 1, Ara h 3, or Ara h 6. Testing several components can help characterize the peanut sensitization profile, but component patterns do not independently establish clinical allergy.
Tree-nut allergens: Immunologic cross-reactivity between peanut 2S albumins and homologous proteins in some tree nuts has been described. However, IgE cross-binding does not establish that a person with Ara h 2 sensitization will react clinically to a particular tree nut.
Pollen-related sensitization: Ara h 8 is a Bet v 1-related peanut component and is associated with pollen-related cross-reactivity. Ara h 8 sensitization represents a different molecular pattern from Ara h 2 sensitization and may be associated with tolerance or predominantly localized oral symptoms in some pollen-sensitized individuals.
Clinical relevance: Cross-reactivity should be interpreted with the patient’s exposure history and symptoms. Positive component results should not be treated as proof of clinically meaningful cross-allergy.