Warfarin monitoring independent of the international normalized ratio (INR): A pilot study

Warfarin monitoring is extended to include an anticoagulant therapy factor (ATF). ATF is shown, using four different thromboplastins (Tps), to be comparable with the International Normalized Ratio (INR) mathematically; but ATF is less cumbersome and does not have the INR's poor precision with up to 13.5% error. ATF is formulated from the prothrombin time (PT), fibrinogen transformation rate (FTR) (a representation of thrombin activity), and a consideration of the fibrinogen (FBG) content of blood plasma. Each of these three components is derived from the optical density (O.D.) changes during both the monitoring of the PT and the following FBG-fibrin conversion by a potentio-photometer (PTPH), a linear-reading spectrophotometric device. Comparison of the ATF with the INR shows correlation coefficients of 0.9474, 0.9248, 0.8116 and 0.8603 using the four respective Tps, and the difference against the mean for Bland-Altman plots averages only 0.2 units more for the ATF than the INR. The ATF is independent of the Tp used, and, although Tp affects the PTs, Tp essentially only initiates the tissue factor pathway (TFP) (extrinsic clotting system) to then obtain the PT. It has no rapid direct effect on thrombin activity. For these reasons, in ATF determination, the kind of Tp used is of no consequence. The ATF is independent of the INR, and numerically almost equal to it. The ATF is, therefore, proposed as a replacement for the INR.