[A modification of a method of evaluating the coagulation activity of factor VIII]

The authors suggest that factor VIII activity be calculated relative to the value of activated partial thromboplastin time of substrate hemophilic plasma. This value is determined by replacing the tested plasma in the reaction mixture with veronal-acetate buffer. This modification has been developed to eliminate the shortcomings of the single-step technique for measuring this factor activity, that are explained by the use of nonstandard donor plasma and by the necessity to have such plasma during the investigation. A formula has been derived for the calculation of factor VIII coagulation activity in hemophilic patients and the advantages of the suggested modification are demonstrated.