Diagnosis of Allergic Reactions to Drugs

Abstract

In diagnosing drug allergies, history, skin testing, some in vitro laboratory tests, and provocation (challenge) testing are the backbone of the investigation. If skin prick testing elicits no reaction, intradermal testing is usually employed. The latter test is more sensitive but produces more false positives. The COADEX classification should be used to assess clinical relevance of positive patch tests. Assays for drug-specific serum IgE antibodies are useful in cases of skin test-negative or equivocal reactors or when skin tests are unreliable/unavailable. In interpreting results of IgE antibody tests, receiver-operating characteristic (ROC) curves provide more information to aid discrimination between positive and negative results. Drug challenge is the best way to confirm an allergic reaction, and it is considered to be the “gold standard” in the diagnosis of drug hypersensitivities. In anaphylaxis, the ratio of total to mature tryptase is typically less than 10. Given the technical improvements made with BAT and the test’s validation for a number of drugs, it continues to be applied to many drug reactions. Non-proliferation-based in vitro assays of cell surface activation markers, cytokines, chemokines, and skin-homing receptors will be increasingly applied to diagnosis. ELISPOT assays (e.g., for IFN-γ and granzyme B) show potential for diagnosis and the chemokine CCL27 and CLA and are promising markers for aiding efforts to understand the relationship between T cells, drugs, and adverse delayed skin reactions.