Assay of plasma thromboplastin antecedent (PTA) with artificially depleted normal plasma.

By HERBERT I. HoRowlrz, WINTHROP P. \Vn cox AND MITSU M. FUJIMOTO R OSENTHAL ET AL. in 19531: described a familial hemorrhagic disorder distinct from classical hemophilia and involving women as well as men. The disorder was attributed to a deficiency of a new blood clotting factor which these authors named plasma thromboplastin antecedent ( PTA ) ; it was present in serum, normal plasma, and plasma adsorbed by BaSO4, precipitated by 25-33 per cent ( NH4 )2 504 and found in Cohn fractions IV-I and III. The International Committee on the Blood Clotting Factors has recently reviewed the properties of PTA and assigned it the designation, factor XI.5 PTA acts early in the sequence of blood coagulation as observed in the test tube. On exposure of blood or plasma to an appropriate surface the Hageman factor ( HF, factor XII ) is adsorbed and activated.0’7 Activated Hageman factor then changes PTA from an inert precursor to an active form, probably synonymous with what Waaler terms the activation product.8 These reactions can occur in the absence of calcium; in the presence of ionic calcium activation product initiates a series of reactions involving factors IX, VIII, X, platelet factor 3 and factor V and leading to the formation of the complete prothrombin converting activity, blood thromboplastin.7 Waaler,8 Margolis6 and Soulier and Prou-Wartelle7 have each shown that in the absence of Ca+ +, the activation product is gradually and irreversibly inactivated in plasma at 37 C. Since normal plasma contains an excess of HF as compared to PTA, it should be possible to find a concentration of activating material which will permit activation and exhaustion of PTA without completely removing HF.#{176}’T The present study applies Waaler’s method for exhausting normal plasma of activation product8 to the assay of PTA deficiency.