Summary
We studied the stability for 24 hr of factor VIII: C and factor Vm C:Ag in plasma
collected in citrate, EDTA or heparin, and confirmed the previously reported two-phase
decay of factor VIII:C in plasma when calcium ions have been chelated. We observed
that plasma factor VIII:C is remarkably stable at 22° C (±2°) when normal calcium
ion concentrations are maintained. The loss of activity of factor VIII:C between one
and 24 hr after blood collection was on average only 0.5% per hr for heparinized plasma.
There was also an apparent loss of factor VIII C:Ag in plasma where calcium ions had
been removed, compared with factor VIII C:Ag in heparinized plasma. However, a comparison
of one-site and two-site assays suggested that calcium chelating agents may lead to
factor VIII C:Ag levels being under-estimated when one-site fluid-phase assays are
employed.
To confirm the action of calcium ions in maintaining factor VIII:C stability, we carried
out a series of experiments where calcium chloride was added four hr after blood collection
to plasma anticoagulated by a mixture of citrate plus heparin; we observed total recovery
of factor VIII:C activity within four hr.
The stability of factor VIII:C, even at room temperature, in the presence of physiological
calcium ion concentrations has implications for manufacturers of factor VIH concentrates
and cryo-precipitates.
Keywords
Factor VIII stability - Heparin - Plasma - Calcium
