Comparison of parallel line skin test assay (PLST) and ELISA inhibition (EI) methods for determination of relative potency of polymerized grass and ragweed antigenic extracts.

Relative potency estimates were performed by parallel line skin test assay (PLST) and ELISA inhibition methods for three polymerized allergen extracts (Bermuda grass, orchard grass, and a copolymer of short and giant ragweed) versus four unmodified RAST standardized reference extracts (Bermuda grass, orchard grass, and giant and short ragweed) in nine subjects. One subject experienced a systemic reaction, requiring treatment at the end of the PLST assay. Another subject had a systemic reaction during limited skin testing performed approximately 72 hours after completion of PLST. Relative potency values for the polymerized extracts obtained by PLST were much lower than those obtained by ELISA inhibition, but results were significantly (r = 0.95; p less than 0.01) correlated. Because polymerized allergen extracts are designed to be hypoallergenic, a skin test assay may underestimate their potency relative to an unmodified reference extract.