Variation in potency of extracts used for allergy skin tests.

Extracts of 11 common inhalant allergens, produced by three different commercial suppliers, were compared by the skin prick test (SPT) in 21 atopic subjects. Good correlation was found between the three brands for positive reactions to grass pollens and English plantain pollen. Eighteen subjects with clinical sensitivity to house dust had diagnostically positive reactions to two of the house dust mite extracts, the third preparation produced no reactions that would be considered as diagnostically significant by the usual criteria. The extracts of house dust mixtures possessed little biological activity and were considered unsatisfactory for accurate diagnostic purposes. One of the three extracts of dog hair and dander produced false positive results in 17 of 21 subjects. The variability of reactions to fungi and animal hair and dander is discussed.