VARIABILITY IN PLASMA PROTHROMBIN CONCENTRATION - IMPLICATIONS FOR USE IN EPIDEMIOLOGY

Recent evidence suggests a major role for prothrombin as a risk factor for thrombosis. However, estimating prothrombin levels from a deficie nt plasma-based clotting assay (factor IIc) is expensive and technical ly difficult in the setting of population-based research. We report th e development of an enzyme-linked immunosorbent assay (ELISA) for prot hrombin using purified antigen and polyclonal anti-prethrombin-1 IgG. Three different quality control plasmas had coefficients of variation (CV) of 6.5%, 4.9%, and 4.8%. Analytical recovery averaged 103.8%. Res ults from the ELISA correlated well with factor IIc results (r = 0.75) . The 5th-95th percentile range for healthy men (n = 10) and women (n = 16) was 97.7 mu g/ml to 161.8 mu g/ml. The assay exhibited no signif icant cross-reactivity with other vitamin-K-dependent proteins. Prothr ombin showed no diurnal variation. In a study of biovariability the an alytical variability, CVA, was 3.1%; the within-subject variability, C VI, was 7.3%; the between-subject variability, CVG, was 14.5%. The cri tical difference for sequential values (i.e. the smallest percentage c hange unlikely to be due to CVA or CVI) significant at P = 0.05 was 21 .9%. The index of individuality, CVI/CVG, was 0.50. On the basis of th e overall biovariability data, primarily the index of individuality, p rothrombin as measured in our ELISA is well suited for applications in population-based research. Blood Coag Fibrinol 9:525-531 (C) 1998 Lip pincott Williams & Wilkins.