Enzyme immunoassay of human protein C by using monoclonal antibodies

An enzyme-linked immunosorbent assay (ELISA) for measuring human protein C by using two monoclonal antibodies directed toward the heavy chain of protein C is reported. This assay enabled the determination of protein C in concentrations of 10 to 400 ng/ml in less than 3 hours with a single antigen-antibody reaction. Within-run and between-run coefficients of variation were less than 8%. The mean concentrations of protein C in plasma of 42 normal subjects, 24 patients with liver disease, 27 with DIC, 48 with warfarin therapy and 15 with congenital protein C deficiency, were 4.2, 3.0, 2.3, 2.1 and 1.9 micrograms/ml, respectively. The results obtained with the present ELISA correlated well with those of radioimmunoassay (r = 0.935, n = 81) as well as those of Laurell's Rocket method (r = 0.910, n = 81) by using rabbit anti-human protein C serum. The present method was sensitive and specific for measurement of protein C and also PIVKA-protein C in plasma.