Sensitivity of Commercial Thromboplastins to Factor VII

Seven commercial thromboplastins and one preparation of human brain thromboplastin were tested for sensitivity to factor VII by two different methods. The prothrombin times of a normal control plasma (100% factor VII), an intermediate plasma (7%), and a severely deficient plasma (<1%) were tested by using eight preparations. A wide range of values was obtained. Quantitative assays for factor VII were performed, and the slope of the regression line was calculated. Wide variability in sensitivity to factor VII was shown for each reagent. The implications of this observation for clinical patient management are discussed.