Introduction: 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.
Method: 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.
Results: 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).
Conclusion: 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.