Diagnostics of cutaneous adverse drug reactions: evaluation of patch tests, lymphocyte transformation tests, and drug provocation tests

Background: Patch tests (PT) and/or lymphocyte transformation tests (LTT) are typically performed, when diagnosed with cutaneous adverse drug reactions (CADR). However, their positivity rates can vary depending on the rash type. Additionally, these tests do not always produce positive results, even when the causative drug is used. Conversely, non-specific reactions can occasionally occur. Objectives: This study aimed to evaluate the positive rates of PT and LTT for different rash types and to analyze the false-positive and false-negative results of these tests in relation to drug provocation outcomes. Methods: This was a retrospective descriptive study. The results of PT, LTT, and drug provocation tests for patients diagnosed with CADR at Department of Dermatology, Kyoto Prefectural University of Medicine, from January 2008 to May 2018, were assessed. Results: A total of 234 patients were diagnosed with CADR, with 43 showing positive reactions to one or more drugs. The highest positivity rate was found in cases of fixed drug eruption. Among the 138 patients who underwent LTT, 44 tested positive for one or more drugs. Drug provocation tests were performed on 31 patients, with 5 exhibiting positive reactions to five drugs. It was observed that three antibiotics produced false-negative results in both PT and LTT. Additionally, antipyretic analgesics yielded false positive results in LTT for 4 patients. Conclusion: It was suggested that the reactivity of PT and LTT could differ based on the rash type. False negatives and false positives might also happen. These factors should be considered when interpreting the test results.