Clotting factor level is not a good predictor of bleeding in carriers of haemophilia A and B

Carriers of haemophilia are known to have a wide range of clotting factor levels and bleeding symptoms. This study aimed at investigating whether carriers of severe and moderate haemophilia had an increased bleeding tendency, compared with a control group, using a condensed version of a bleeding assessment tool developed by the Molecular and Clinical Markers for the Diagnosis and Management of Type 1 VWD study group (MCMDM-1VWD). One hundred and twenty-six genetically verified carriers of severe and moderate haemophilia and 90 controls were interviewed regarding bleeding symptoms. A bleeding score of at least 4 was considered positive, indicating a significant bleeding tendency. Clotting factor levels were tested in the carriers.Nineteen of the women were carriers of haemophilia B, with a mean factor (F)IX:C level of 0.54 (± 0.27) kIU/l, and 107 were carriers of haemophilia A, with a mean FVIII:C level of 0.74 (± 0.32) kIU/l. The median bleeding score was 2 (-3-12) among carriers and -1 (-3-8) among controls (P < 0.001). The bleeding score was weakly correlated to clotting factor levels in carriers of haemophilia A (rs = -0.36, P < 0.001). We conclude that the bleeding tendency in our cohort of carriers differed significantly from that in the controls and that clotting factor levels might not be sufficient to predict the bleeding tendency.