EVALUATION OF THE PRO-TRAC TACROLIMUS MONOCLONAL WHOLE-BLOOD ENZYME-LINKED-IMMUNOSORBENT-ASSAY FOR MONITORING OF TACROLIMUS LEVELS IN PATIENTS AFTER KIDNEY, HEART, AND LIVER-TRANSPLANTATION

In a prospective study, we evaluated a novel enzyme-linked immunosorbe nt assay (ELISA) (Pro-Trac) for determining tacrolimus (FK 506) concen trations in whole blood. Results obtained by the ELISA were compared w ith those obtained either by microparticle enzyme immunoassay (MEIA) o r by high-performance liquid chromatography/mass spectrometry (HPLC-MS ). The lower limit of quantitation of the ELISA was 0.5 mu g/L. The wi thin-series coefficient of variation (CV) was <11%. For spiked blood s amples containing different concentrations of tacrolimus, interassay C V was 23.6% at 2.5 mu g/L; however, at 15 and 60 mu g/L, interassay CV was 44.9 and 50.8%, respectively. In crossover studies including bloo d samples from patients after liver, heart, or kidney transplantation, ELISA results correlated with those of the HPLC-MS (r = 0.73) as well as with those generated by MEIA (r = 0.82). The ELISA and MEIA showed 52.3 and 56.2% cross-reactivity with 15-O-demethyltacrolimus, respect ively, but only 5.0 and 5.4% cross-reactivity with 13-O-demethyltacrol imus. We conclude that if assay precision in the upper range is improv ed, the Pro-Trac ELISA might be a valuable alternative to the MEIA for therapeutic drug monitoring of tacrolimus.