First prospective report on immune tolerance in poor risk haemophilia A inhibitor patients with a single factor VIII/von Willebrand factor concentrate in an observational immune tolerance induction study.

INTRODUCTION/BACKGROUND: Development of neutralizing inhibitors against factor VIII (FVIII) is a major complication of haemophilia A treatment. AIM: The ongoing, international, open-label, uncontrolled, observational immune tolerance induction (ObsITI) study evaluates ITI, the standard of care in patients with inhibitors. PATIENTS/METHODS: Forty-eight prospective patients in this interim analysis received a single plasma-derived, von Willebrand factor-stabilized, FVIII concentrate (pdFVIII/VWF) for ITI. According to recommended Bonn protocol, 'low responders' at ITI start (<5 BU) received 50-100 IU FVIII kg(-1) daily, or every other day; 'high responders' (≥5 BU) received 100 IU FVIII kg(-1) every 12 h. RESULTS: Forty of 48 patients (83.3%), had at least one risk factor for poor ITI-prognosis at ITI start (i.e. age ≥7 years, >2 years since inhibitor diagnosis, inhibitor titre ≥10 BU at the start of ITI, or prior ITI failure). Nonetheless, 34 patients (70.8%) achieved complete success, 3 (6.3%) partial success, 1 (2.1%) partial response; ITI failed in 10 patients (20.8%), all with poor prognosis factors. All six low responders achieved complete success. ITI outcome was significantly associated with inhibitor titre level at ITI start (P = 0.0068), number of poor prognosis factors for ITI success (P = 0.0187), monthly bleeding rate during ITI (P = 0.0005) and peak inhibitor titre during ITI (P = 0.0007). Twenty-two of 35 high responder patients (62.9%) with ≥1 poor prognosis factor achieved complete success. CONCLUSION: Treatment with a single pdFVIII/VWF concentrate, mainly according to the Bonn protocol, resulted in a high ITI success rate in haemophilia A patients with inhibitors and poor prognosis for ITI success.

Coagulation factor activity and clinical bleeding severity in rare bleeding disorders: results from the European Network of Rare Bleeding Disorders.

BACKGROUND: The European Network of Rare Bleeding Disorders (EN-RBD) was established to bridge the gap between knowledge and practise in the care of patients with RBDs. OBJECTIVES: To explore the relationship between coagulation factor activity level and bleeding severity in patients with RBDs. PATIENTS/METHODS: Cross-sectional study using data from 489 patients registered in the EN-RBD. Coagulation factor activity levels were retrieved. Clinical bleeding episodes were classified into four categories according to severity. RESULTS: The mean age of patients at data collection was 31 years (range, 7 months to 95 years), with an equal sex distribution. On linear regression analysis, there was a strong association between coagulation factor activity level and clinical bleeding severity for fibrinogen, factor (F) X, FXIII, and combined FV and FVIII deficiencies. A weaker association was present for FV and FVII deficiencies. There was no association between coagulation factor activity level and clinical bleeding severity for FXI. The coagulation factor activity levels that were necessary for patients to remain asymptomatic were: fibrinogen, > 100 mg dL(-1); FV, 12 U dL(-1); combined FV + VIII, 43 U dL(-1); FVII, 25 U dL(-1); FX, 56 U dL(-1) ; FXI, 26 U dL(-1); FXIII, 31 U dL(-1). Moreover, coagulation factor activity levels that corresponded with Grade III bleeding were: undetectable levels for fibrinogen, FV and FXIII, < 15 U dL(-1) for combined FV + VIII; < 8 U dL(-1) for FVI; < 10 U dL(-1) for FX; and < 25 U dL(-1) for FXI. CONCLUSIONS: There is a heterogeneous association between coagulation factor activity level and clinical bleeding severity in different RBDs. A strong association is only observed in fibrinogen, FX and FXIII deficiencies.