Mild hemophilia A with factor VIII assay discrepancy: using thrombin generation assay to assess the bleeding phenotype

Summary.  Introduction:  In some patients with mild hemophilia A, there are discrepancies between 1-stage (1-st) and 2-stage (2-st) factor VIII (FVIII) clotting assays, and also chromogenic assays for FVIII activity (FVIII:C). We examined whether thrombography could provide a better evaluation of the hemostatic status of these patients. Methods:  Two families with such discrepancies and markedly contrasting clinical histories were studied. Family X had no serious bleedings, in contrast to family Y. Sixty-one moderate/mild hemophiliacs without discrepancy and 15 healthy subjects served as controls. Calibrated automated thrombography was performed with platelet-rich plasma after one freeze-thawing cycle and low tissue factor concentration. Results:  The chromogenic FVIII:C levels were higher (0.90 ± 0.15 and 0.47 ± 0.13 IU mL⁻¹) than the 1-st clotting ones (0.14 ± 0.05 and 0.10 ± 0.05 IU mL⁻¹) in family X and Y, respectively ( P  < 0.001). Mean endogenous thrombin potential (ETP) was 1579 ± 359 n m  min⁻¹ and 1060 ± 450 for healthy controls and hemophilic controls, respectively. For members of family X, the ETP values were 1188, 1317 and 2277 n m  min⁻¹, whereas for those of family Y they ranged from 447 to 1122 n m  min⁻¹. Two novel missense point mutations were evidenced: p.Ile369Thr in family X and p.Phe2127Ser in family Y. In family X, we postulate that the mutation is responsible for a delayed but non-deleterious FVIII activation. Conclusions:  Our results suggest that the hemostatic phenotype assessed by thrombography may be clinically relevant in moderate/mild hemophilic patients with discrepant FVIII:C results.