An Artificial ‘Haemophilic’ Plasma for One‐Stage Factor‐VIII Assay

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Abstract
An artificial plasma for 1-stage factor VIII assays was made by incubating human plasma with EDTA to destroy factor VIII, and afterwards removing the anticoagulant by dialysis. Bovine factor V was then added to a given level. In the assay, contact activation was controlled by adding contact product. Factor VIII activity was destroyed and the EDTA was freely dialyzable. The fibrinogen in the treated plasma clotted normally with thrombin. Likely variation in the factor V activity was not critical. The concentration of fibrinogen and other factors was adequate. Variation between batches was small. The artificial plasma yielded assay results closely comparable to hemophilic plasma in samples with factor VIII activities from 0.01-20.0 IU/ml. The mean results in the artificial system were estimated 0.997 times those in hemophilic plasma, with a 95% confidence interval of 0.901-1.103. Biological variability in individual assays was smaller in the artificial system than when hemophilic plasma was used. Instability at the bench was detected more often in the artificial system than in hemophilic plasma assays, but the effect was eliminated from the results by obtaining duplicated readings in a balanced order.