[Diagnostic possibilities in drug allergies].

Drug allergies can be subclassified into three subgroups, which differ in their pathophysiology and require different diagnostic steps: (1.) classical drug allergies, which are directed to the drug itself, a reactive compound of the drug, or some contamination of it; (2.) pseudo-allergic reactions, which are caused by non-immune mediated degranulation of mast cells and basophils, and (3.) autoimmune reactions, in which the drug elicits an immune reaction to autologous structures. A very detailed (criminalistic) history has the highest priority for clarification of a suspected drug allergy. In addition, skin tests, serological tests and the lymphocyte transformation test may be useful. It is necessary to differentiate between tests which imitate the drug elicited allergic reaction (i.e. Coombs test in drug induced hemolytic anemia) and tests which only indicate sensitization. The detection of IgG antibodies to drugs bound to various carriers (nitrocellulose, sepharose) is controversial and the meaning of a positive result is unclear. Therefore, this test cannot be recommended for the routine diagnosis of drug allergy. Special emphasis is placed on the value of the lymphocyte transformation test, which is more often positive than other test procedures and may sometimes strengthen the suspicion that a disease may be caused by a drug. Nevertheless, this test requires cautious interpretation as it may be falsely positive as well as falsely negative.