Progress report of an external quality assessment scheme for cyclosporine assay

Beginning in 1987, an external quality assessment (EQA) scheme for cyclosporine (CsA) assay was organized by our Institute and supported by National Research Council (CNR); in 1991, the CNR EQA joined the French CsA interlaboratory program organized by Service de Radiopharmacie et Radioanalyse, University of Lyon. During the last 2 years (1993 and 1994 cycles), > 170 laboratories (from seven European countries) participated in this survey, assaying 44 control samples prepared from pooled blood of heart- and renal-transplant patients; normal pools added with known amounts of CsA were also distributed. During the whole EQA period, a trend toward the use of specific and nonisotopic techniques has been observed. In 1994, 91% of the collected results have been produced by specific methods [high-pressure liquid chromatography (HPLC) or specific immunoassays developed to assay the native molecule of CsA without its metabolites];in the same cycle, the fully automated techniques [TDx, fluorescence polarization immunoassay (FPIA), and enzyme-multiplied immunoassay (EMIT)] accounted for 73% of total results. CsA concentration measured by monoclonal specific immunoassays [(TDx FPIA, radioimmunoassay (RIA) Cyclo-Trac, and EMIT] was well correlated with those from HPLC (r = 0.99-1.00); results from EMIT were very close to those from HPLC, whereas results from RIA Cyclo-Trac and TDx were slightly overestimated (10-20%). Nonspecific methods (TDx polyclonal and nonspecific RIA Cyclo-Trac) measured CsA concentrations 3-4 times higher than those found by HPLC. The cross-reactivity of CsA metabolites in specific immunoassays was estimated from data of patients' samples and spiked samples; an interference of 6% in RIA Cyclo-Trac, 7% in EMIT, and 26% in TDx FPIA was found. The precision coefficient of variation (CV% between laboratory and between assay) of the methods observed in the 1994 EQA cycle was 9.5 for TDx polyclonal FPIA, 10.4 for TDx monoclonal FPIA, 10.5 for EMIT, 10.6 for RIA specific Cyclo-Trac, 14.2 for RIA nonspecific Cyclo-Trac, and 15.2 for HPLC.