Biological standardization of allergenic extracts.

Accurate and precise methods of skin testing are essential for "in vivo" standardization of extracts from the same and different sources, for diagnostic efficacy as well as an important prognostic factor for evaluating the risk and benefit of immunotherapy. Skin test methods such as parallel line bioassay and ID50EAL which are based on the intradermal erythema response and yield the most sensitive, accurate, and precise bioassays as well as requiring the fewest injections and replicates should be preferentially selected for clinical use. Differentiating characteristics of parallel line bioassay and the ID50EAL method are presented. Proficiency test methods for assessing puncture and intradermal skin test methodologies should be made part of the clinicians' training and be incorporated into clinical practice in conjunction with standardized allergenic extracts. Assignment of Allergy Units to reference extracts based on accurate and precise "in vivo" methods such as the ID50EAL and to test extracts based on "in vitro" assays predictive of their "in vivo" relative potency as determined by parallel-line bioassay should facilitate the safe and effective clinical use of allergenic extracts.