In vitro diagnosis of drug allergy. Assessment of the chromatin activation test (CAT).

A controlled in vitro study was performed on people suspected to be allergic to one or more drugs by using the chromatin activation test. This test is based on the decrease of the nuclear lymphocyte birefringence induced by stimulation with allergens. A group of 70 patients with suspected drug hypersensitivity and a control group of 37 persons were studied. Fifty-two patients were evaluated by clinical criteria and the cause-effect relationship classified as definitive, probable, possible, improbable and not related. Previously, 18 patients had been considered allergic to penicillin by means of RAST and/or skin tests. The chromatin activation of the peripheral lymphocytes was determined by comparing the nuclear birefringence of cells incubated with different sequential drug concentrations, with that detected in cells incubated without drugs, employing a polarized light microscope. When possible, the oral challenge was carried out in the negative cases. In 123 tests made in the patient group, 45 were positive and distributed as follows: in the cases of definitive imputability (83.3%), probable (60.5%), possible (22.7%), improbable (0%) and not related (0%); in the cases with RAST and/or skin positive tests (33.3%). Thirty-two of 36 oral tests confirmed those results. Among 50 tests performed in the control group, two (4%) were false positive. These results point to the usefulness of this test in the diagnosis of drug allergy. Copyright 1997 John Wiley & Sons, Ltd.