Background: The diagnosis of a drug allergy is mainly based upon a very detailed history and the clinical findings. In addition, several in vitro or in vivo tests can be performed to demonstrate a sensitization to a certain drug. One of the in vitro tests is the lymphocyte transformation test (LTT), which can reveal a sensitization of T-cells by an enhanced proliferative response of peripheral blood mononuclear cells to a certain drug.
Objective: To evaluate the sensitivity and specificity of the LTT, 923 case histories of patients with suspected drug allergy in whom a LTT was performed were retrospectively analysed.
Methods: Based on the history and provocation tests, the probability (P) of a drug allergy was estimated to be > 0.9, 0.5-0.9, 0.1-0.5 or < 0.1, and was put in relation to a positive or negative LTT.
Results: Seventy-eight of 100 patients with a very likely drug allergy (P > 0.9) had a positive LTT, which indicates a sensitivity of 78%. If allergies to betalactam-antibiotics were analysed separately, the sensitivity was 74.4%. Fifteen of 102 patients where a classical drug allergy could be excluded (P < 0.1), had nevertheless a positive LTT (specificity thus 85%). The majority of these cases were classified as so-called pseudo-allergic reaction to NSAIDs. Patients with a clear history and clinical findings for a cotrimoxazole-related allergy, all had a positive LTT (6/6), and in patients who reacted to drugs containing proteins, sensitization could be demonstrated as well (i.e. hen's egg lysozyme, 7/7). In 632 of the 923 cases, skin tests were also performed (scratch and/or epicutaneous), for which we found a lower sensitivity than for the LTT (64%), while the specificity was the same (85%).
Conclusion: Although our data are somewhat biased by the high number of penicillin allergies and cannot be generalized to drug allergies caused by other compounds, we conclude that the LTT is a useful diagnostic test in drug allergies, able to support the diagnosis of a drug allergy and to pinpoint the relevant drug.