Isoniazid in patient plasma may cause a false-positive result on the complement-dependent cytotoxicity test

Correct definition of clinically relevant anti-HLA antibodies is important for transplant organ allocation and outcome. We describe a candidate for kidney transplantation who was treated with isoniazid because of active tuberculosis. The patient's serum gave a positive antibody result on screening with the complement-dependent cytotoxicity (CDC) test but a negative result on screening with a bead-based assay (Luminex). The clinical history indicated no immunologic stimuli. Subsequent testing on fresh serum samples confirmed the discrepancy between CDC and Luminex results. An autologous cross-match test gave negative results, and the antibodies were sensitive to dithiothreitol treatment. We postulated that nonspecific binding of drug-antibody complexes to panel lymphocytes in the CDC test may have caused the observed lympholysis. This case, although isolated, emphasizes the importance of the combined use of CDC and solid phase assays. The CDC results alone would have led to the erroneous conclusion that the patient was highly sensitized.