COMPARING R-TISSUE FACTOR AND MAMMALIAN TISSUE REAGENTS FOR PROTHROMBIN TIME

We compared two recombinant human tissue factor (r-TF) prothrombin tim e (PT) reagents with two commercially available mammalian PT reagents. The two r-TF reagents were more sensitive to the lower concentrations of factors II, VII, IX, and X. The r-TF preparations were found to gi ve longer clotting times than the mammalian thromboplastins when plasm a samples from oval anticoagulant-treated patients were tested. When i nternational normalized ratios (INRs) were calculated, however, no sig nificant differences were noted among reagents when INR values were le ss than or equal to 3.0; however, at INR values greater than 3.0, diff erences were noted. The r-TF was more sensitive to the thrombin inhibi tors than were heparins. Because of different origins and composition, the currently available thromboplastin reagents are not equivalent, a nd the results obtained from these should be interpreted carefully.