MEASUREMENT OF FACTOR VII AND OF ACTIVATED FACTOR VII IN HEALTHY INDIVIDUALS AND IN PROTHROMBIN COMPLEX CONCENTRATES

We established reference ranges for factor VII clotting activity (FVII:C), factor VII amidolytic activity (FVII:AM), and activated factor VII (FVIIa) in 102 healthy individuals. The reference ranges were 65-160 U/100 ml, 70-165 U/100 ml, and 30-170 mU/ml, respectively (2.5 and 97.5 percentiles). Freezing and thawing of the plasma samples had no influence on the assay results. Due to the small sample size, the results were not influenced by gender, age, smoking habits, and oral contraceptive use. The plasma levels of FVII:C, FVII:AM, and FVIIa were significantly correlated with each other. The significant correlation between FVIIa and FVII:AM indicates that FVIIa is not completely independent of circulating FVII mass. There was also a significant, though weak, correlation between FVIIa and FVII:C/FVII:AM ratios. Sixteen batches of prothrombin complex concentrates (PCC) from 3 manufacturers were also analysed. FVIIa could be detected in all preparations, with considerable variations from batch to batch. In contrast to the results obtained in plasma from normal individuals, there was a close correlation between FVIIa and FVII:C/FVII:AM ratios. The preparations could be characterized by their FVII and FVIIa potencies and by their FVII:C/FVII:AM ratios. In PCC, FVII:C was very strongly correlated with FVIIa, whereas no significant correlation was observed between FVII:AM and FVII:C and between FVII:AM and FVIIa, respectively. These results demonstrate that the FVII:C assay used is sensitive for detecting FVIIa. Thus, we cannot confirm that FVIIa sensitivity of one-stage clotting assays for FVII:C is low when a rabbit thromboplastin and a non-adsorbed FVII-deficient plasma is used.