Sandwich Enzyme lmmunoassay of Cystatin C in Serum with Commercially Available Antibodies

We developed a sandwich enzyme immunoassay for de-termining cystatin C in serum by usingcommercially avail-able antibodies. We optimized each assay step (e.g., concentrations of coating rabbit anti-human cystatin C antibodies and horseradish peroxidase-conjugated anti-bodies) and studied the binding kinetics of antigen and antibodies. The within-assay cv was <5%, the between-assay CV was 8.8%, the detection limitwas 0.9 /.Lg/L,and the assay can be performed within 2 h. Cystatin C con-centrations in sera from men were significantly higher than in women (mean and SD: 2.14 ± 0.31 vs 1.78 ± 0.26 mg/L). We studied the cystatin C concentrationsin sera of 31 outpatients with suspected kidney damages to char-acterize the behavior of this Iow-M, protein as a possible indicator for estimating the glomerular filtration rate. Th