Concordance between crude extract and component allergens in a multiple allergen simultaneous test: a large-scale...

Multiple allergen simultaneous tests (MAST) increasingly incorporate both crude extract and molecular component allergens for specific IgE testing. However, systematic data on the diagnostic concordance between these two approaches remain limited. We evaluated the agreement between crude extract and corresponding component allergen results using a MAST panel in a large clinical laboratory cohort.

We retrospectively analysed deduplicated MAST results from a high-volume referral laboratory over a two-month period. For 29 crude extract allergens paired with 48 corresponding component allergens, positivity rates were assessed using a cutoff of class 2 or higher (≥0.70 IU/mL). Concordance was defined as both crude extract and at least one component allergen being positive, or both being negative. Agreement was evaluated using percent agreement and Cohen's kappa coefficient.

A total of 19,949 patients were included. The highest positivity rates were observed for Dermatophagoides farinae (31.8%), D. pteronyssinus (29.9%), rDer f 2 (24.2%), and cat epithelium (12.2%). Overall percent agreement exceeded 90% for most allergen pairs, primarily driven by high negative agreement. Cohen's kappa revealed substantial agreement (κ ≥ 0.6) for ten allergens including D. farinae, cat dander, and birch pollen, whereas eight allergens including D. pteronyssinus and milk showed poor agreement (κ < 0.1) due to low component allergen positivity despite positive crude extract results.

Diagnostic concordance between crude extract and component allergen testing in MAST varies substantially across allergen sources. These findings underscore the need for allergen-specific interpretation guidelines when reporting MAST results incorporating component allergens in clinical laboratories.