The Role of Skin and Provocation Tests

The diagnostic value of skin tests has not been fully evaluated during the last decade. Reliable skin test procedures are generally lacking, and test concentrations are unknown or poorly validated for most drugs (De-moly 2005). Skin prick tests and intradermal tests are particularly important for reactive haptens in order to demonstrate an IgE-dependent mechanism. They should be performed 4-6 weeks after the reaction by specialists in an appropriate setting, since the tests themselves can induce an anaphylactic reaction, although rarely.

Depending on the drug, the sensitivity and predictive values of tests vary from excellent (penicillin, muscle relaxants) to satisfactory (opioids, thiopental) all the way to poor or unknown (local anesthetics, paracetamol, sulfonamide, contrast media, nonsteroidal anti-inflammatory drugs). For details, see Sects. 4.7 and 4.8.

The best standardized skin test exists for the |3-lac-tam ring of penicillin. An IgE-dependent hypersensi-tivity can be demonstrated by a positive skin prick test and/or intradermal test after 20 min (Brockow et al. 2002).

A drug provocation test is carried out for diagnostic/therapeutic purposes and consists of the controlled administration of the drug to a patient with a history that suggests drug allergies. The European Network of Drug Allergy from the European Academy of Allergology and Clinical Immunology recommends the use of a provocation test when skin tests and biological tests are not available or not validated. This approach has elicited some controversial discussion, because with the exception of aspirin and |3-lactams, results of tests are only available for very small patient groups. One of the most important reports on drug provocation tests, con ducted in 1,372 patients, could show true drug hypersensitivity in only 17.6% ofthepatients (Demoly2005). This is of crucial importance for the therapeutic future of these patients. Drug provocation tests should nevertheless be regarded as a serious and potentially dangerous procedure (Aberer et al. 2003).

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