Influence of matrix effect upon cyclosporine A test by fluorescence polarization immunoassay and enzyme-multiplied immunoassay technique methods

Objective To explore the matrix effect on cyclosporine A (CsA) test by fluorescence polarization immunoassay (FPIA) and enzyme-multiplied immunoassay technique (EMIT), explain the discrepancy of external quality control results between these two methods and find the corrective action.Methods One hundred whole blood samples with various concentrations were adopted and CsA levels were detected by FPIA and EMIT.The results were compared with each other.Moreover, the influence of residual metal ions upon immunoreactions was assessed by adding Cu2+ and Zn2+.The effect of non-whole blood matrix on extraction efficiency for quality control materials and CsA calibrator was evaluated by adding identical volume of Hb-rich reagents followed with re-extraction.Results There is good correlation between results measured with FPIA(X) and EMIT(Y) methods ( Y=0.926 8X -8.115,R2 =0.996 9).Neither FPIA nor EMIT was affected by residual metal ions ( P ＞ 0.05 ). Non-whole blood matrix decreased the extraction efficiency of two methods, but it could be corrected by supplementation of the Hb-rich reagents (≥30 g/L).Conclusions Non-whole blood matrix may be the main reason for the inconsistent results measured by FPIA and EMIT methods.It could be corrected by using Hb-rich reagents.In addition,we should consider the influence of low lib on CsA test,espocially for organ transplant patients with lower Hb ( ＜30 g/L). Key words: Cyclosporine;  Fluorescence polarization immunoassay;  Enzyme multiplied immunoassay technique;  Quality control;  Evaluation studies