DETERMINATION OF ACTIVATED FACTOR VII BY BOVINE AND RABBIT THROMBOPLASTINS.

Thromboplastins from different animal species vary in their relative sensitivity to non-activated VII and activated VII (Vila) in plasma and this has formed the basis of Vila determinations using bovine and human thromboplastins. Since the use of human thromboplastin is now being discontinued we have re-evaluated the assessment of Vila using bovine and rabbit thromboplastins (BT and RT respectively). Citrated plasma was prepared from four normal individuals and maintained at 4°C in glass containers for 24 hours to promote the formation of Vila. Each plasma was subsampled at 0, 2, 4, 6 and 24 hours and factor VII assays performed using BT and two different rabbit preparations viz, (a) Manchester Reagent (RTmr, ISI = 1.16) and (b) Diagen phenolised (RT diagenlSI = 1.4). Results were expressed as the ratio BT/RT. With all thromboplastins factor VII activity increased with time. The changes were most marked using BT with much smaller increments occurring using the rabbit preparatrions. RTmr was less sensitive to Vila than RT diagen. The ratio BT/RTmr thus provides an index of Vila.

Using this method we determined Vila in plasma samples from 29 normal subjects. Results obtained were x = 1 ,00;s.d. = 0.126; normal range 0.72 - 1.25 The method was applied to 29 plasma samples from 19 patients with disseminated intravascular coagulation giving BT/RTmr = 1.71 (range 0.92 - 3.38). We conclude that the ratio of Factor VII measured by bovine and rabbit thromboplastins respectively provides an index of Factor VII activation in plasma.