Prothrombin level in coumarin-treated patients. A peculiar effect observed in a one-stage system using certain substrates

Viper venoms and coumarin-induced prothrombin. A comparison of several one-stage methods employing three different venoms as thromboplastins

Three venoms obtained from three vipers, namely Echis carinatus, Notechis scutatus scutatus and Oxyuranus scutellatus, have been used as thromboplastin in a one-stage assay of coumarin-induced prothrombin. Regardless of the venom used, prothrombin resulted to be low in coumarin-treated patients. The mean values obtained were 27.2, 33.6, and 24.2%, respectively. These values were comparable to those obtained by means of the classical one-stage method (24.8%). A good correlation was observed among the different methods. However, the levels observed using the Notechis scutatus scutatus venom method were slightly higher as compared to those obtained by means of the other viper venoms and by means of the classical one-stage method. The three viper venoms used seem unable to activate coumarin-induced prothrombin. The levels obtained were in fact, in each instance, definitely lower than those observed immunologically. Methods which employ these viper venoms may be used in the evaluation of prothrombin in coumarin-treated patients.

The K-test (trypsin clotting time) in coumarin treated patients and in congenital deficiencies and abnormalities of the prothrombin complex

The behavior of K-test (Trypsin clotting time) has been studied in 38 patients on long-term coumarin therapy and in 19 patients with congenital coagulation disorders of the prothrombin complex. All coumarin treated patients showed a clear prolongation of the test. The results obtained were compared with the standard prothrombin time, the Hepato-Quick-test (P-P test) and the Factor II + X test values, observed in the same patients. A good correlation was observed in each instance. The highest correlation was observed between K-test and the Factor II + X test (r=+0,78;t=7,80;p less than 0.001). All congenital coagulation disorders of the prothrombin complex yielded a prolonged K-test value but for Factor VII deficiency. In three patients with this latter condition a perfectly normal value was obtained. The K-test together with the prothrombin time may be useful in the differential diagnosis of factor VII deficiency from factor X deficiency and from the factor X Friuli abnormality.