Assessing skin prick tests reliability in ECRHS-I.

Abstract

Atopy, the clinical definition of an immunoglobulin E (IgE) high-responder, can be documented either by the detection of IgE antibodies in serum or by a positive skin prick test. Epidemiological studies use different reaction sizes to define a skin test reaction as positive or negative. The aim of the study was to identify the best cut-off level for skin prick tests. Using the data collected during the European Community Respiratory Health Survey (ECHRS I) the association of serum allergen-specific IgE and skin prick tests [Dermatophagoides pteronyssinus (Der p), cat, timothy grass and Cladosporium] were assessed. The proportion of the 11 355 subjects (49.9% men), with positive skin tests ranged from 10.4% (cut-off >5 mm) to 20.9% (cut-off >0 mm) for Der p, 3.5-10.2% for cat, 9.3-16.6% for timothy grass and 0.2 and 2.3% for Cladosporium. For identifying subjects with detectable specific IgE (>0.35 kU/l) the most appropriate cut-off appeared to be over 0 mm for Der p, cat and timothy grass (Youden Index over 0.81). However, the relationship between serum IgE and skin prick test for Cladosporium was weak (Youden index under 0.56). In epidemiological studies, a single method may be chosen to assess allergenic sensitivity. A cut-off level of over 0 mm for skin prick tests was best at identifying those with allergen-specific IgE.