Determination of prothrombin concentration as an index of anticoagulant control

Abstract

N SPITE OF the intensive efforts of many hematologists, the precise sequence of events producing coagulation of blood remains obscure. The application of results of in vitro studies to an understanding of coagulation in vivo has proved a troublesome and perilous transition to the clinician in his attempt to devise effective means for the prevention of intravascular thrombosis and embolism without at the same time invoking the hazard of hemorrhage. The increasing use of coumarintype anticoagulants for long periods in both hospitalized and ambulatory patients has brought into focus the deficiencies in the present methods used to determine appropriate therapeutic administration of these drugs. The one-stage prothrombin test of Quick has been the method of choice for years, in spite of the realization of its shortcomings.‘-” Several authors have reported the value of determining prothrombin concentration during anticoagulant therapy.’ ,3,4~5.6,g~12 It is the purpose of this paper to present further observations on the value of prothrombin concentration determinations during anticoagulant therapy with warfarin (Coumadin@) sodium. METHODS Two groups of fifty and 280 patients, respectively, were studied. During an 18 month period, 2,500 blood samples were collected for the simultaneous determination of the one-stage prothrombin time by the method of Quick”,14 and the prothrombin concentration by the Biggs modification of the OwrenAas method.6visri@ Simultaneous determination of proconvertin (factor VII) concentration by the method of Owren and Aas was performed in twelve of the patients in group 1 and in five of the patients in group 2. The laboratory determinations were performed the same morning that the blood samples were drawn. All of the laboratory determinations of the concentration of prothrombin and proconvertin were performed by the same technician. “Quality control” was utilized in the prothrombin determination.16