Potential role of the dynamic properties of whole blood coagulation in assessment of dosage requirements in haemophilia

In the clinical setting, patients suffering from haemophilia are classified according to the residual level of the deficient coagulation factor. Patients suffering from the severe form of haemophilia (critical factor level <0.01 IU mL(-1)) display some heterogeneity in their tendency to bleeding despite the uniform factor level. Utilizing a new thrombelastographic method in which coagulation is activated by very small amounts of tissue factor and where resulting data are processed with new software, we studied the whole blood coagulation profile in 11 patients with severe haemophilia A and 11 patients with moderate haemophilia. In both groups of patients, we found a considerable degree of heterogeneity in the coagulation signal. In moderate haemophilia with factor VIII (FVIII):C levels between 0.01 and 0.05 IU mL(-1), variance was expected, whereas a quite substantial diversity had not been forecasted in patterns of the whole blood coagulation profiles in patients with the severe form of haemophilia A. Ex vivo substitution to patient's blood to reach various theoretical levels of recombinant factor VIII (rFVIII) revealed that the coagulation response to FVIII supplementation varied substantially. In some severely affected patients levels of FVIII:C close to 0.05 IU mL(-1) was sufficient to normalize the coagulation profile, while others required a dose giving >0.50 IU mL(-1) of FVIII to achieve a normal whole blood clotting profile. In conclusion, our study revealed that severe haemophilia A seems not to be a single entity, but rather several different clinical and biochemical phenotypes, and that the response to added FVIII varies amongst patients.