Prothrombin time in the monitoring of oral anticoagulant: a comparison of results using different thromboplastins.

The objective of this report is to compare the prothrombin time performed with thromboplastin of different tissues and species in patients under oral anticoagulant therapy as well as the way of expressing the results. The results showed that the ISI of the thromboplastin of human and rabbit brain are very close to the IRP BCT/253 (1.2 vs 1.1) and RBT/79 (1.3 vs 1.4), respectively. In contrast, the rabbit lung thromboplastin showed the greatest differences in the ISI values (1.6 vs 1.4) and in the CV (6.1%). The authors found significant statistical differences with the results of the prothrombin time as expressed in activity percentage (p less than 0.001) in three plasma pools of patients under different oral anticoagulant level for all thromboplastins studied. However, if the results are expressed in terms of INR, the values obtained are almost the same. The results here reported would demonstrate that the prothrombin time as INR allows the use of only one scheme for oral anticoagulant control when the thromboplastin reagent is calibrated according to the recommendations of the WHO.