THE STRONG POSITIVE CORRELATION BETWEEN FACTOR-VII CLOTTING ACTIVITY USING BOVINE THROMBOPLASTIN AND THE ACTIVATED FACTOR-VII LEVEL

We compared factor VII clotting activity (FVIIc) assays using differen t thromboplastins to determine which is the most sensitive for activat ed FVII (FVIIa) or for FVII antigen (FVIIag). FVIIc levels were measur ed using thromboplastins derived from bovine brain (FVIIc Bov), human placenta (FVIIc Hum), and rabbit brain (FVIIc Rab). FVIIa levels were measured by fluorogenic assays using human soluble tissue factor (rsTF ) or bovine rsTF. We also measured FVII activity by an amidolytic assa y (FVIIc:am Hum) using human thromboplastin and a chromogenic substrat e for thrombin. FVIIag levels were determined by ELISA. In the FVIIa a ssay, the reaction time obtained from using bovine rsTF was shorter th an that with human rsTF, suggesting that the interaction of plasma FVI Ia with bovine rsTF was stronger than with human rsTF. The plasma FVII a levels measured using human rsTF and bovine rsTF were almost the sam e (r=0.947, p<0.0001). Among the three FVIIc assays, FVIIc Bov had the strongest positive correlation with the plasma FVIIa level (r=0.886, p<0.0001), but had no correlation with FVIIag. An increase of 1 ng/ml in the plasma FVIIa level yielded a 27.9% increase of FVIIc Bov. Plasm a FVIIc Hum and FVIIC:am Hum showed moderate correlations with both FV IIa (r=0.520, p<0.02 and r=O.569, p<0.01, respectively) and FVIIag (r= 0.438, p<0.05 and r=O.468, p<0.05, respectively). FVIIc Rab had the lo west correlation with FVIIa (r=0.367, p<0.1), but had a moderate col r elation with FVIIag (r=0.436, p<0.05). After in vitro cold activation, FVIIc Bov levels increased the most and FVIIc:am levels showed the le ast change. These findings indicate that consideration of the thrombop lastin used for assay is necessary when assessing the clinical signifi cance of FVII activity as a cardiovascular risk factor.