1977 Volume 8 Issue 2 Pages 320-325
Usefulness of normotest (NT) in management of oral anticoagulant therapy was studied in comparison with Quick's prothrombin time (PT) or thrombotest (TT).
Twentysix male and seven female patients with thromboembolism on long-term warfarin treatment (mean maintenance dose; 3.9mg per-day) were subjected. Control samples were obtained from youg doctors and laboratory technicians.
1. Effect of temperature on PT, NT and TT activities of oxalated plasma samples stocked for 0, 24 or 72 hours at -20, 4 or 22°C was investigated.
NT was most stable among three tests.
2. Reproducibility of the results in normal subjects or patients by three different technicians (A: beginner, B: more expert, C: the most expert technician) was investigated. Both reproducibility and reliability were highest in NT. Procedures of both NT and TT were equally simple as compared with PT.
3. The following correlations among activities of PT, NT and TT were observed; between PT and NT: Y=0.806X+9.29, PT and TT: Y=0.590X+3.43, NT and TT: Y=0.719X-3.30.
Correlation coefficients were 0.813, 0.793 and 0.929, respectivelly. (p<0.001).
4. In 8 normal subjects, PIVKA inhibitor ranged -0.15 to 0.25 (mean±sd; 0.094±0.148), while 33 patients under warfarin therapy, the index ranged 0.13 to 0.59.
There was significant negative correlation between the inhibitor and TT, although no correlation of NT to the inhibitor was observed. In addition, the coincidence rate of therapeutic range was higher between NT and PT than that of TT and PT.
Although prothrombin time has long been used for anticoagulant therapy, there still remains problem to be solved. That the therapeutic range of clotting activity of 15-30% was determined by short time difference of 7 seconds is one of them.
In addition, there are a certain technical difficulty and troublesome procedures such as centrifugation and standarization of tissue thromboplastin used.
While thrombotest is expected to be sensitive to all vitamin K dependent clotting factors including IX and endogenous inhibitors.
The problem is that sensitivity of this test is not superior to PT.
Determination of therapeutic range in NT is easier than in PT because of longer time difference of 60 seconds.
Thus, the NT is useful, convinient and reliable method for management of anticoagulant therapy in spite of insensitivity to endogenous inhibitor and factor IX.