Madhvi Rajpurkar

Inhibitors in factor IX deficiency a report of the ISTH-SSC international FIX inhibitor registry (1997–2006)

Summary.  Haemophilia B is an X‐linked disorder resulting in coagulation factor IX deficiency. Patients with severe deficiency (<1% factor IX activity) may have significant bleeding complications similar to patients with haemophilia A or factor VIII deficiency. The development of inhibitory antibodies to the missing coagulation factor is a major complication in patients with haemophilia. While the incidence of inhibitors in patients with haemophilia A is higher than that in haemophilia B, the occurrence of allergic and or anaphylactic reactions with the development of inhibitors is unique to haemophilia B patients. Since haemophilia B is a rare bleeding disorder and the incidence of inhibitors is an even rarer entity, a registry was established by Dr Indira Warrier under the auspices of the FVIII/FIX subcommittee of the International Society of Thrombosis and Haemostasis, to gather information on the occurrence and characteristics of patients with inhibitors and also the incidence of allergic and anaphylactic reactions in this group of patients. This is the first report from this registry and helps us to gather some insight on haemophilia B patients with inhibitors and complications related to inhibitor development and difficulties with immune tolerance.

Thromboelastography in children with coagulation factor deficiencies

Hemophilia is traditionally classified according to the levels of the deficient coagulation factor as Severe (<1%), Moderate (1–5%) or Mild (>5%). However, it is well known that the factor activity does not necessarily correspond to the clinical bleeding manifestations. As prophylactic therapy is the best method of prevention of serious complications such as hemophilic arthropathy, a test that may predict the bleeding pattern would be extremely beneficial. Thromboelastography (TEG) uses whole blood to determine clot formation characteristics, such as initiation, propagation as well as strength of the clot, and is now being extensively studied in bleeding and thrombophilia. This study attempted to determine the TEG characteristics in 47 children with moderate hemophilia (MH) and severe hemophilia with (SHI) and without inhibitors (SH) and tried to retrospectively correlate them to the clinical bleeding patterns. TEG showed evidence of faster and better clot formation, as evidenced by a higher maximum thrombin/fibrin generation, in those with mild bleeding manifestations compared to those with severe bleeding tendency, in addition to the expected prolongation in time to formation of clot related to factor deficiency. This may be a potentially useful tool to evaluate the bleeding tendency and determine need for prophylaxis in children with hemophilia.

Crucial role for the VWF A1 domain in binding to type IV collagen

Von Willebrand factor (VWF) contains binding sites for platelets and for vascular collagens to facilitate clot formation at sites of injury. Although previous work has shown that VWF can bind type IV collagen (collagen 4), little characterization of this interaction has been performed. We examined the binding of VWF to collagen 4 in vitro and extended this characterization to a murine model of defective VWF-collagen 4 interactions. The interactions of VWF and collagen 4 were further studied using plasma samples from a large study of both healthy controls and subjects with different types of von Willebrand disease (VWD). Our results show that collagen 4 appears to bind VWF exclusively via the VWF A1 domain, and that specific sequence variations identified through VWF patient samples and through site-directed mutagenesis in the VWF A1 domain can decrease or abrogate this interaction. In addition, VWF-dependent platelet binding to collagen 4 under flow conditions requires an intact VWF A1 domain. We observed that decreased binding to collagen 4 was associated with select VWF A1 domain sequence variations in type 1 and type 2M VWD. This suggests an additional mechanism through which VWF variants may alter hemostasis.

Tissue plasminogen activator induced fibrinolysis: standardization of method using thromboelastography.

Fibrinolysis is a complex physiological process that involves the interaction of several anticoagulant proteins. Defects of the fibrinolytic system are extremely difficult to diagnose and study because there are no standardized tests available. Thromboelastography is a novel method that allows the study of both coagulation and fibrinolysis using one sample of whole blood, thereby allowing a more physiologic assessment of the coagulation process. Several in-vitro studies have been attempted to determine whether thromboelastography would be a useful assay for the study of fibrinolysis but have reported problems with reproducibility and reliability. Here we report the process involved in developing a thromboelastographic assay in which tissue plasminogen activator (t-PA) is used to induce fibrinolysis. The assay was standardized to ensure that the concentration of the coagulation inducer (tissue factor) and fibrinolytic agent (t-PA) was adequate to induce a clot with lysis parameters that were reproducible and reliable. This method can be used to rapidly assess the intrinsic fibrinolytic potential of whole blood. Our assay showed that it could rapidly predict high levels of plasminogen activator inhibitor, and this information would be beneficial in patients with acute stroke or myocardial infarction.

How do you treat bleeding disorders with desmopressin

Desmopressin is an analog of vasopressin that exerts a substantial haemostatic effect by inducing the release of von Willebrand factor from its storage sites in endothelial cells. It has proved useful in treating or preventing bleeding episodes in patients with von Willebrand disease, haemophilia A and platelet function defects. Its efficacy in achieving a satisfactory level of haemostasis has reduced the use of blood products to treat bleeding episodes. Clinicians need to become familiar with the use of this drug that has become a home medication for many patients with inherited bleeding disorders.

Immune tolerance induction in 31 children with haemophilia A: is ITI less successful in African Americans?

Summary.  Inhibitor development continues to be a major problem in the treatment of haemophilia. Immune tolerance induction (ITI) continues to be the most effective approach to managing this complication. This study reviews the practice and outcome of ITI at a single centre over a 17‐year period. All 31 inhibitor patients have haemophilia A. Two patients with haemophilia A underwent two trials of ITI and a third patient underwent three trials of ITI for a total of 35 courses of ITI in these 31 patients. Most patients had high responding inhibitors, 22 of 31. Seventy‐one percent of haemophilia patients achieved tolerance. Courses of ITI in African American (AA) patients with haemophilia A were much less likely to achieve tolerance compared with non‐AAs, 57.9% and 92% (P = 0.04) respectively. Most trials of ITI were carried out with recombinant products (25 of 35). While ITI continues to be an effective therapy for patients with inhibitors, it is less effective in AA patients, and patients with higher inhibitor titres. In this refractory group of patients, new approaches are needed.

Ethanol lock therapy for the treatment of catheter‐related infections in haemophilia patients

Summary.  Central venous access devices (CVAD) are increasingly being used for optimal delivery of clotting factor concentrates in patients with haemophilia with poor peripheral venous access. The utility of CVAD is particularly well recognized in young patients starting factor prophylaxis and in patients with inhibitors undergoing immune tolerance induction (ITI). A catheter‐related infection (CRI) remains the most common complication of CVAD in haemophilia patients and is the most frequent indication for its removal. Additionally, in some patients the infection results in significant morbidity and mortality and also contributes to failure of the ITI regimen. Ethanol‐lock therapy (ELT) is a treatment modality that has been used to treat CRI in patients with indwelling catheters for home parenteral nutrition and chemotherapy. The aim of this study was to report the success in treating CRI in haemophilia patients using ELT. Three severe haemophilia A patients undergoing ITI regimen who developed CVAD infections resistant to conventional management with antibiotics were treated by ELT according to the institutional technique. All three patients responded well to ELT with clearance of the CVAD infection. There were no adverse side effects. To our knowledge, this is the first report of ELT in patients with haemophilia. The role of ELT needs to be investigated in larger studies for treatment of CRI in patients with bleeding disorders.

Thromboelastography identifies children with rare bleeding disorders and predicts bleeding phenotype.

Rare bleeding disorders (RBDs) comprise 3–5% of all congenital bleeding disorders. They can evade typical coagulation screening tests and there is a poor correlation between laboratory results and bleeding phenotype. Thromboelastography (TEG) measures coagulation globally in whole blood samples. The aims of this study were to evaluate the utility of TEG as an adjunct to the routine screening tests employed for the diagnosis of RBDs and to correlate TEG results with the bleeding phenotype in RBDs. TEG parameters and clot kinetics were compared to bleeding phenotypes (asymptomatic, mild, moderate and severe) in 26 RBD patients and 30 normal controls. Clot kinetics correlated strongly with RBDs and with the severity of bleeding phenotype with mean maximum rate of thrombus generation (MRTG) 15.4 mm min−1 in controls vs. 6.0 in RBDs (P < 0.0001, Wilcoxin). The mean MRTG was 7.7 in mildly symptomatic, 5.5 in moderately symptomatic and 4.1 in severely symptomatic patients (P < 0.0001, Kruskal–Wallis). Disorders that are often missed by conventional screening tests, dysfibrinogenaemia and platelet disorders displayed a distinctive TEG curve with markedly decreased maximum amplitude (MA) and low MRTG values. Factor XIII and PAI deficient patients displayed increased fibrinolysis in addition to low MRTGs. All patients with RBDs, but none of the normal controls, had abnormal clot kinetics suggesting that TEG may be an effective screening test for RBDs.

Use of recombinant activated factor VII in patients with Glanzmann's thrombasthenia: a review of the literature.

Glanzmanns thrombasthenia (GT) is a rare bleeding disorder characterized by a quantitative or qualitative defect of glycoprotein IIb/IIIa on the platelet membrane. Managing bleeding episodes is often difficult, and a variety of modalities have been used, including platelet transfusions, recombinant factor VIIa (rFVIIa), and other supportive care. The aim of this review was to present the clinical experience with rFVIIa bolus infusion (rFVIIa BI) for treatment of bleeding episodes and prevention of bleeding during surgical procedures in patients with GT. A literature search was performed to identify rFVIIa‐treated patients with GT. Overall, one international survey, one open‐label study, and 40 case reports identified 172 bleeding episodes treated with rFVIIa and 62 procedures covered with rFVIIa. In the international survey, rFVIIa BI was used for 96 bleeding episodes in 59 patients. Recombinant FVIIa was effective in 76 bleeding episodes (79%). Of 34 surgical procedures, 25 procedures received rFVIIa BI with 92% bleeding‐prevention efficacy. The open‐label study reported 28 patients with 28 rFVIIa BI‐treated bleeds, and 26 (93%) bleeding episodes responded to rFVIIa. Published case reports revealed that 25 (69%) of 36 bleeds and 27 (96%) of 28 surgeries responded to rFVIIa BI treatment. Overall, 26 adverse events were reported in 19 patients, including five thromboembolic events in two patients where a possible relationship with rFVIIa could not be excluded. Two large studies and 40 case reports provide a literature base to support the efficacy and safety of rFVIIa BI in patients with GT.

Fluctuations of anti‐Xa concentrations during maintenance enoxaparin therapy for neonatal thrombosis

Aim:  To evaluate fluctuations in anti‐Xa concentrations in infants treated with enoxaparin for thrombosis and describe clinical outcomes.