Evidence-based diagnosis in patch testing.

Evidence-based medicine (EBM) is defined as the integration of the best research evidence with clinical expertise and patient values. Based on the principles of EBM, we can conclude that patch testing is cost-effective only if patients are selected on the basis of a clear-cut clinical suspicion of contact allergy and only if patients are tested with chemicals relevant to the problem (high pretest probability). Random patch testing (low pretest probability) should be discouraged. Proper pretest probability assessment can only be done in expert centres, because problem-based testing requires both a thorough knowledge of the patch-test procedure and knowledge about potential sensitizers in a specific environment.