7-2.b. Value of in vitro tests
The in vitro diagnostic method most frequently used for diagnosing delayed HSRs is the lymphocyte transformation test (LTT). This test identifies the proliferation of drug-specific T cells from patients with HSR upon the stimulation with the suspected drug(s) by measuring the incorporation of [3H].62 However, to our knowledge there is only one study using this method with PPI. In this study LTT was performed in 28 subjects with occupational allergy to omeprazole diagnosed by positive patch test results. From these patients, 23 showed a positive LTT result, yielding a sensitivity of 82%. From the 56 subjects with negative patch test results, 46 showed a negative LTT, yielding a specificity of 82%.87 Another study has analyzed the role of drug lymphocyte activation test (LAT) measuring granulysin and interferon-γ in 69 cases of PPI delayed reactions including SJS/TEN and DRESS.71 They found that LAT measuring granulysin had a sensitivity of 59.3% and specificity of 96.4%.