The V-twin system (Dade Behring Laboratories): a useful tool for immunosuppressive drug monitoring

The predose trough cyclosporine (CsA) level (C0) was widely used to assess the possibility of drug nephrotoxicity. Owing to its potential limitation as an indicator of total drug exposure, 2-hour postdose (C2) monitoring has been considered to be a more accurate marker. The V-Twin analyzer (Vital SC, Netherlands) conceived for EMIT technologies (Dade Behring Laboratories) is proposed herein to determine CsA levels using a specific calibrator without any dilution, as well as tacrolimus (FK) and mycophenolate mofetil (MMF) levels. Both CsA (C0: n = 133 and C2: n = 55) and FK (n = 121) EMIT assays were compared to the RIA CsA assay (DiaSorin Laboratory) and to the MEIA tacrolimus assay (Abbott Laboratory), respectively. In addition, the feasibility of MMF EMIT assay was evaluated. Overall, 309 transplant patients were included in this study. For all parameters tested, total imprecision studies were lower than 10%, and the coefficient of linearity was r(2) > .99. For the CsA kit, the range of linearity was between 25 and 500 ng/mL for the C0 and 400 and 2000 ng/mL for the C2 assay. The values obtained were highly correlated with the RIA for the C0 levels (EMIT = 0.9 RIA+3.66; r = .97) and for the C2 levels (EMIT = 0.89 RIA-14.2; r = .956). Similar results were obtained with the EK EMIT kit, with a linearity range between 3 and 30 ng/mL, and a high concordance with the MEIA test (EMIT = 0.98 RIA+1.09; r = .96). Preliminary MMF results in 59 sera, containing from 0.1 to 30 microg/mL, showed that this examination could be included as a routine. The V-twin system is a useful tool for routine monitoring with a single method for C0 and C2 cyclosporine, tacrolimus, and mycophenolate levels.