Allergenic extracts are biologically active products which retain the ability to trigger an immune response. The intensity of this response is a general representation of the relative biological strength, or potency, of an extract.
The FDA requires that all standardized allergenic extracts be tested for potency and then labeled with a specific potency value. This value is derived using a parallel-line assay that measures either the mass units of a major allergen or the inhibition of IgE-antigen binding. In each case, a newly manufactured lot of extract is compared to a reference extract to estimate the new product’s “relative” potency.
Such a measure of potency, however, represents only a single parameter of an allergenic extract. The potency value by itself may not reveal important differences in an extract’s allergen composition. Therefore, it is important to understand how an extract’s potency is determined and how this relates to the product’s clinical performance.