Determination of the stability of diluted allergen extracts using a concentration step prior to EAST inhibition

Background Generally the stability of diluted allergen extracts, as used for skin testing, provocation testing and immunotherapy can not be measured using a normal enzyme allergosorbent test (EAST) inhibition method.Objective The aim of this study was to determine the stability of diluted allergen extracts using an ultrafiltration step prior to the standard EAST inhibition procedure, in which the allergen extract was concentrated 100-fold.Methods This concentration procedure was validated for Dermatophagoides pteronyssinus, timothy pollen, birch pollen and cat dander extracts and used in a stability study in which three batches were stored for 1 year at 6 degrees C and 25 degrees C.Results There was no difference in relative potency before and after concentration of birch and timothy pollen extracts. D. pteronyssinus and cat dander extracts showed a significant decrease of 25% and 35% of the relative potency after concentration. The mean coefficient of variation of 12 determinations of the stability study was 11.8%.Conclusion For all allergens the 30 BU/mL or approximately 0.00025 mg/mL solution was stable for 12 months at both temperatures, except for D. pteronyssinus which declined rapidly at 25 degrees C.