Monitoring Cyclosporine in Liver-Transplant Recipients: Effects of Clinical Status on the Performance of Two Monoclonal Antibody-Based Methods

The characteristics of the Abbott selective fluorescence polarization immunoassay for cyclosporine in whole blood (mxsP) were compared with the lncstar radioimmunoas-say by using kit standards (INC8P) or TDXSP standards (INcTDx)with samples from adult (48) and pediatric (24) liver-transplant recipients and a further 32 control speci-mens. The rDxsP assay was faster, less labor intensive, and more precise at higher concentrations; it gave results a median of 5 zg/L lower than INCSPvalues, irrespective of biliary 1-tube status, patient’s age, or severity of cholestasis in nine patients, comparisons being made for serum bilirubin more than eight times normal or <50 jLmol/L. However, both assays overestimated INCTDXval-ues by-10%. There was a progressive increase in the ratio of TDXSP to both INCSP and INCTDX results in 57 samples stratified in relation to serum bilirubinconcentra-tions. Cross-reactivity of TDXSP with cyclosponne metab-olites Ml (23%) or Ml 7 (12%) was greater than for INCSP (15 % and 5%, respectively) or INCTDX(22 % and 4%, respectively), but the converse was true with M21 (2 % fo