A comparison of EMIT and FPIA methods for the detection of cyclosporin A blood levels: Does impaired liver function make a difference?

Objective: Apparent cyclosporin A (CSA) blood levels, as determined by fluorescence polarization immunoassay (FPIA) and enzyme-multiplied immunoassay technique (EMIT), were compared in CSA-treated patients with various degrees of liver dysfunction. Methods: FPIA and EMIT were performed in parallel according to test manufacturer instructions in blood from kidney (n = 82), liver (n = 96) and heart transplant (n = 20) patients. Results: The precision of both techniques was greatest in patients with the highest blood levels, and at each blood level greater for the FPIA than for the EMIT. Apparent CSA blood levels, as determined by EMIT, were typically approximately 70% of those determined by FPIA, indicating greater cross-reaction of the antibody in the FPIA with CSA metabolites. However, the ratio of values determined with EMIT and FPIA was very similar in kidney, liver and heart transplant patients. Among liver transplant patients it was also very similar in those without major alterations of hepatic function and in those with impaired excretory (increased bilirubin and γGT) or synthetic (i.e., reduced thromboplastin time) function. Extended storage of blood samples for up to 10 days did not affect apparent CSA blood level estimates by EMIT in a clinically relevant manner. Conclusions: We conclude that the greater specificity of the antibody in the EMIT for the CSA parent compound does not translate into a clinically relevant advantage for CSA monitoring.