By replacing the three crude reagents commonly used in thromboplastin generation tests—washed platelets, barium sulfate- or alumina-adsorbed plasma, and serum—with purified clotting factors, many variables and uncertainties were eliminated. It was demonstrated that plasma thromboplastin antecedent (PTA) was required for the generation of thromboplastic activity.

A method was developed for the preparation of purified PTA from fraction IV-1 of human plasma. Its identity was established by its ability to correct, in vitro, the defect in the plasma of a PTA-deficient patient. Thus, further evidence in support of the belief that PTA is a discrete component, essential for blood coagulation, was obtained. More specifically, it was found to be essential in the generation of thromboplastic activity in plasma.

A test system for thromboplastin generation was described which was used to assay PTA in vitro and which did not require the use of PTA-deficient plasma or serum. Omission of any one of the components of this system resulted in a marked loss of thromboplastic activity; restoration of activity was proportional to the amount of the component that was added. Thus, with this system of purified components, it was possible to assay any one of them without the use of, or requirement for, plasma or serum specimens from patients with specific coagulation deficiencies.

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