Assay of factor VII activity by two techniques: evidence for increased conversion of VII to αVIIain hyperlipidaemia, with possible implications for ischaemic heart disease

Abstract

Factor VII was assayed in healthy adults and pregnant women by a coagulation method (VII_c) and a procedure (VII_t) based upon activation of factor X. Although VII_c and VII_t were highly correlated (r 0.8) they apparently measured different aspects of VII activity. This difference was related to plasma lipid concentrations. Plasma VII_c showed independent positive associations in vivo with VII_t, cholesterol and triglyceride concentrations, but was unaffected by in vitro adjustment of plasma lipoprotein concentrations. The difference between assays might be due to differing reactivities of VII. The VII_c assay measures VII in its in vivo proportions as the single-chain protein and fully active double-chain form (αVII_a). In VII_t, all VII is converted to αVII_a before measurement. Thus an increase in VII_c but not VII_t with increasing lipid concentrations reflects an increased proportion of VII as αVII_a, possibly secondary to activation of the contact system. This effect may explain at least part of the increased VII_c and normal VII_t in pregnancy, and the increased VII_c of hyperlipidaemias in general. The relative values of VII_c and VII_t are proposed as a measure of flux within the coagulation system, and as a measure of coagulability in hyperlipidaemia and other states.