OC 70.5 - Bleeding in non-severe haemophilia A and B – data from the PedNet study group.

Background: The clinical observation that bleeding phenotype is milder in haemophilia B has never been established in large datasets.

Aims: To compare bleeding patterns between children with non-severe haemophilia A and B.

Methods: Haemophilia patients included in the PedNet Registry (Clin.gov.trial-NCT02979119) by January 1st, 2020 with baseline factor FVIII/FIX activity between 1%-25% (0.01 UI/mL-0.25 UI/mL) with follow up information available, were included in this study. Patients were followed from diagnosis to: January 1st, 2020, 18 years of age, start of prophylaxis, or inhibitor diagnosis. ABRs and A(J)BRs were established by negative binomial modelling. Onset of bleeding was analysed using Kaplan-Meier survival. Groups were compared using regression analysis and Log Rank tests, respectively.

Results: 825 patients were included: 237 moderate HA, 92 moderate HB, 404 mild HA and 92 mild HB patients. Total follow up was 5249 patient years for HA, 1354 patient years for HB. Median age at last FU was 9.7 years (IQR 6.0 – 13.8) for HA, 8.6 years (IQR 5.0 – 12.6) for HB.
Onset of bleeding was comparable between haemophilia types. Median age at first bleed was 3.7 years (95%CI 3.1 – 4.3) for HA vs 4.8 years (95%CI 3.5 – 6.1) for HB (p-value 0.432). Median age at first joint bleed was 10.8 years (95%CI 9.2 – 12.4) for HA vs >12.5 years for HB (p-value 0.167).
Moderate HA showed a more severe bleeding type in both ABR (1.12 in HA vs 0.47 in HB, p< 0.001) and AJBR (0.29 vs 0.10, p=0.001)(Figure 1). For mild haemophilia, bleeding rates were very low and appeared similar in HA and HB: ABR 0.21 vs 0.16 (p=0.212), AJBR 0.05 vs 0.03 (p=0.283).

Conclusion(s): Moderate HA patients have a significantly more severe phenotype than moderate HB. Bleeding tendency in mild haemophilia was very low and no differences between the two types were observed.