FACTOR-VII-DEFICIENT SUBSTRATE PLASMAS DEPLETED OF PROTEIN-C RAISE THE SENSITIVITY OF THE FACTOR-VII BIOASSAY TO ACTIVATED FACTOR-VII - AN INTERNATIONAL STUDY
Gj. Miller et al., FACTOR-VII-DEFICIENT SUBSTRATE PLASMAS DEPLETED OF PROTEIN-C RAISE THE SENSITIVITY OF THE FACTOR-VII BIOASSAY TO ACTIVATED FACTOR-VII - AN INTERNATIONAL STUDY, Thrombosis and haemostasis, 71(1), 1994, pp. 38-48
Plasma from healthy individuals, pregnant women and patients on warfar
in were distributed to 3 laboratories supporting major cardiovascular
surveys (Northwick Park, Muenster and Houston) for assay of factor VII
Coagulant activity (VII(c)) with their own bio-assays. The mean VII(c
) in 147 samples agreed to within 1% of standard in Northwick Park and
Houston, but was 14% of standard lower in Muenster owing to its more
potent standard. In samples with an increased VII(c) the Northwick Par
k assay gave a higher result than the other assays owing to its increa
sed responsiveness to activated factor VII (VII(a)). Thus when VII(a)
concentrations were determined directly with a clotting assay which ut
ilises a soluble recombinant tissue factor, the increase in VII(c) wit
h increase in VII(a) was considerably greater with the Northwick Park
assay than the Muenster assay. This feature of the Northwick Park assa
y was traced to the virtual absence of protein C in its substrate plas
ma. Factor V(a) appears rate-limiting for the coagulant expression Of
VII(a) in test plasma. If the thrombotic response to release of tissue
factor is determined by the circulating concentration of VII(a), then
the Northwick Park factor VII bio-assay may be preferable to other bi
o-assays currently employed to estimate risk of acute coronary events.