Summary. 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 . 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 dLfor 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.

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 plasmaderived, 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 À1 daily, or every other day; 'high responders' (≥5 BU) received 100 IU FVIII kg À1 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.

To investigate renal function in a group of patients with a history of haemophilia and haematuria. We reviewed 32 medical records of the patients with haemophilia and gross haematuria identified through a computerized haemophilia registry, from January 1993 to December 2004. In all patients but three (two refused to participate and one died) clinical and laboratory tests were performed by the nephrologist. One patient had chronic renal failure because of diabetic nephropathy. In two patients reduced renal function was detected by creatinine clearance measurements, and one of them had Duchenne muscular dystrophy. In four patients minimal proteinuria was diagnosed by the biuret method. Mild reduction in renal function of unknown cause was found in only one of the 29 patients tested.

3312 The European Network of Rare Bleeding Disorders (EN-RBD) was established to bridge the gap between knowledge and practice in the care of patients with RBDs (rare bleeding disorders frequency <1/0.5-2M). The aim of this first report was to explore the relationship between the coagulation factor activity levels and clinical bleeding severity in patients with RBDs. A total of 592 records on patients with RBDs were cross-sectionally collected over a period of three years. Data on clinical bleeding episodes were available for 495 patients and were classified into four categories according to severity. The mean age of patients was 31 years (range, 7 months-95 years), with 51% being females. On linear regression analysis, there was a strong association between coagulation factor activity level and clinical bleeding severity for fibrinogen, factor (F)FX, 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. It is of clinical relevance to identify levels that are not associated with spontaneous major bleeding, which was done by constructing receiver operating characteristic curves. These levels were highest for FXIII deficiency (25 U/dl), followed by FV+VII (15 U/dl), FVII (15 U/dl), FX (5 U/dl), and FV (1 U/dl) deficiencies. For fibrinogen deficiency, a factor activity level of 20 mg/dl is needed to ensure absence of major spontaneous bleeding. There is a clear relation between coagulation factor activity level and clinical bleeding severity in RBDs, which is different for the missing clotting factor. Disclosures: Peyvandi: NovoNordisk, CSL Behring: Honoraria. Bidlingmaier:CSL Behring, Bayer Schering: Research Funding; CSL Behring, NovoNordisk, Pfizer, Bayer Schering: Membership on an entity's Board of Directors or advisory committees; Baxter, Biotest, CSL Behring, NovoNordisk, Pfizer, Bayer Schering: Honoraria. Schved:LFB, CSL Behring, Novonordisk, Bayer Schering: Research Funding.

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