Stuart Clotting Defect. I. Segregation of an Hereditary Hemorrhagic State from the Heterogeneous Group Heretofore Called “Stable Factor” (SPCA, Proconvertin, Factor VII) Deficiency

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Abstract
A patient was restudied who had been diagnosed previously as hypoproconvertinemia (SPCA or factor VII deficiency). The patient''s prolonged one-stage prothrombin time was not corrected by Russell viper venom (Stypven) and his serum lacked a factor essential for a normal thromboplastin generation test. The clotting defect was corrected by SPCA deficient plasma. The factor deficient in this patient, therefore, differs from all hitherto described coagulation factors and is being called the Stuart factor after the surname of the proband. The Stuart factor appears to have unusual actions, being necessary early in "blood thromboplastin" formation and required for optimal activity of brain, lung and platelet thromboplastin, cephalin and viper venom. Stuart factor is relatively heat and pH stable and can be separated from platelets by a single wash in saline. It cannot, however, be removed from the sedimentable coagulant (Product II) formed by incubation of normal serum, AHF, platelets and Ca. The concentration of the Stuart factors is lowered by Dicoumarol therapy. Assay procedures for "proconvertin" and "factor VII" using asbestor-adsorbed plasma as substrate are probably sensitive to changes in levels of both SPCA and Stuart factor. The hemorrhagic states previously classified as congenital "hypoproconvertinemia" or "SPCA deficiency" or "factor VII deficiency" are a heterogeneous group; there are at least two separable conditions included within this category.