Comparison of specific radioimmunoassays for cyclosporine

This study compares two recently introduced radioimmunoassay kits involving specific monoclonal antibodies to cyclosporine. One kit (Sandimmun) involved 3H-labeled CsA (3H-CsA) as tracer and the other (CY-CLO-Trac-SP) involved a 125I-labeled conjugated derivative of CsA. The kits were nearly equivalent in method performance characteristics. They produced superimposed standard curves and equivalent values to transplanted patient samples. Concentrations of CsA determined by either kit were apparently equivalent to values measured by high-performance liquid chromatography, suggesting that the specific monoclonal antibodies used with the kits detect in trough blood mainly native CsA. The 125I-labeled CsA, when compared with the 3H-CsA alternative, increased the sensitivity and precision, decreased the turnaround time, and provided a technically efficient and conveniently capable method of replacing HPLC for measuring native CsA.