Allergy screening including a comparison of prick test results with allergen-coated lancets (Phazet®) and liquid extracts

During an allergy screening of families with a history of allergy in one or more subjects, skin prick tests (SPT) were performed in duplicate in 314 adults. The tests were performed with a new type of lancet with a 0.9 mm long point, loaded either with allergen (Phazet) or used together with standardized extracts (10,000 and 100,000 BU/ml). Wheals obtained with both methods were compared, and related to total IgE concentrations and history. A wheal area of 3 and 7 mm2 was used as cut-off limit. Results with Phazet were close to those with Pharmalgen 100,000 BU/ml. With both methods precision was good for allergens, but less for Phazet histamine than for the corresponding wet test. SPT results obtained with Phazet and 100,000 BU/ml correlated better with history than the results with 10,000 BU/ml. Using a wheal size of 7 mm2 as cut-off limit the efficiency for five tested allergens was 91%. "False positive" tests, possibly indicating an unobserved or latent type of allergy, were found more often with higher serum IgE concentrations. The safety of SPT was confirmed and Phazet was well accepted by nurses and tested subjects.