Summary
A number of different methods are available for the measurement of factor VIIa. Almost
all of these employ ratios of two different measurements of factor VII. In order to
determine which is the most sensitive to activated factor VII we have compared currently
available methods in the following groups: two patients with haemophilia A following
treatment with activated recombinant factor VII (rVII a); 6 normal plasmas during
cold promoted activation of factor VII; normal individuals (n = 23); and patients with unequivocal disseminated intravascular coagulation (DIC,
n = 19). Factor VII was measured in an amidolytic assay (VII: Amid) and an antigen
assay (VII:Ag). Clotting activity was measured using rabbit (VII:C Rab), human (VII:C
Hum) and bovine (VII:C Bov) thromboplastin.
Of the clotting assays the most sensitive to the presence of factor VIIa was that
which utilised bovine thromboplastin. Amidolytic and immunological measurements were
unaffected by the activity state of factor VII. The ratios VII:C Rab/VII: Ag and VII:C
Rab/VII:Amid were insensitive to activated factor VII. The ratios most sensitive to
the presence of factor VII a were VII:C Bov/VII: Amid and VII: C Bov/VII:Ag. The ratios
VII:C Bov/VII:C Rab and VII:C Bov/VII:C Hum are less sensitive but have the advantage
for epidemiological studies of narrower reference ranges.
