The batch‐to‐batch variation of the potency of dog– and cat–allergen‐coated lancets

In clinical work I formed the impression that the potency of Phazet® lancets, for cat and dog allergens, was lower than earlier and too low to diagnose all clinically sensitive children with cat and dog allergy. Therefore, I decided to investigate the potency of newly produced and several years old Phazet lancets coated with dog and cat allergens. Twenty‐six adults with case histories of cat and/or dog allergy and skin reactive to extracts of either dog dander or cat epithelium were skin prick tested in duplicate with one old batch and one newly produced batch of Phazet dog and/or cat lancets as well as the in‐house reference of cat and/or dog allergen, 100 000 BU/ml. The potency of Phazet lancets in relation to the standard was evaluated by the median slope of the allergen dose‐response relationship. The potency of the old dog lancets (mean 48 900 BU/ml) was higher (NS) than that of the newly produced lancets (mean 28 000 BU/ml), and the potency of both types of lancets was significantly less (P<0.001) than that of the dog allergen in‐house standard. On the other hand, the potency of newly produced (123 000 BU/ml), but not old (108 000), cat‐allergen‐coated Phazet lancets was higher than that of the cat allergen in‐house reference extract (P = 0.048). There was a marked variation in potency between patients. Most of this variation was due to factors varying between patients, not between lancets, indicating that the composition of the allergen on the lancets was partly different from that of the standard. The results indicate that skin prick tests must be used for the batch control of allergen‐coated lancets and that such lancets used in scientific work must be calibrated against a standard by skin prick testing.