The
bleeding phenotype has been suggested to differ between
haemophilia A and B. More knowledge on the
bleeding phenotype at initiation of treatment is important to optimize patient care. The aim of this study was to investigate the severity of the
bleeding phenotype and the variation in
bleeding in children with severe or moderate
haemophilia A and B. Consecutive, previously untreated patients with severe or moderate
haemophilia A and
B (factor VIII or IX activity <0.01 or 0.01-0.05 IU mL(-1) respectively) born between January 1st 2000 and January 1st 2010 were included. Primary outcome was severity of
bleeding tendency. Secondary outcome was variation in
bleeding pattern. A total of 582 patients with severe
haemophilia A and 76 with severe
haemophilia B did not differ in age at first exposure to
clotting factor (0.81 vs. 0.88 years, P = 0.20), age at first bleed (0.82 vs. 0.88 years, P = 0.36), and age at first joint bleed (1.18 vs. 1.20 years, P = 0.59). Patients with moderate
haemophilia were older compared to patients with severe
haemophilia. In patients with moderate
haemophilia there were no clear differences between
haemophilia A and B. Severity and variation in
bleeding phenotype are similar during the early stage of treatment in patients with severe and moderate
haemophilia A and B respectively. The findings imply that children with
haemophilia B should be observed and treated as vigilantly as those with
haemophilia A.