RESUMEN
Thromboplastin is a tissue extract used in the prothrombin time test (PT) necessary for oral anticoagulant control. The interlaboratory variability of the results of the PT test with thromboplastins of different tissue types, besides differences due to reporting PT in seconds or percentage, indicate the need for a standardized reference thromboplastin in order to express PT results on a common scale. The aim of the present work is to encourage the laboratory hospital either singly or in regional groups, to produce a standardized thromboplastin for their own use, to insure the control of oral anticoagulant therapy. Rabbit brain thromboplastin was prepared by Quick's technique. The reagent was calibrated against the international reference thromboplastin RBT/079, following the recommendations of the World Health Organization (WHO). Statistical analyses of the data were performed using an orthogonal regression. We obtained an international sensitivity index (ISI) of 2.177, a standard error of 0.0454 and a coefficient of variation of 2.09%. An international normalized ratio (INR) was also obtained for the conversion of measured PT to a common scale. The INNSZ thromboplastin is the first national reference preparation. With this reagent the introduction of an international scale for the control of oral anticoagulant therapy has become feasible in our country.