[Initial experiences with a recombinant human tissue thromboplastin in oral anticoagulation]

A recombinant tissue factor (rTF, Batch TFS-RD3, Baxter Diagnostics) has been assessed by plasma and capillary blood methods and compared with our working rabbit brain thromboplastin (CRB Roche, Basel, Switzerland) for its suitability in monitoring oral anticoagulant therapy. The international sensitivity index (ISI) for rTF calibrated against CRB has been found to be 0.73 and 0.69 respectively. The slope of the orthogonal regression line between log prothrombin time rTF plasma and rTF capillary blood is 0.96. Thus, we considered the ISI to be identical for both methods. International normalized ratios calculated with these assumptions, and even activity percentages assigned by a dilution curve, did not differ from the results obtained with our working thromboplastin. The human recombinant thromboplastin TFS-RD3 seems to have properties similar to currently used commercial thromboplastins. Recombinant tissue factor as a well defined preparation could make essential contributions to the standardization of prothrombin time and to the improvement of oral anticoagulant therapy.