Low Von Willebrand Factor Activity Research Articles

Discrepant low von Willebrand factor activity results on the ACL TOP analyzer are frequent in unselected patients with myeloproliferative neoplasms and show no correlation with high-molecular-weight multimer loss or bleeding phenotype

BackgroundBleeding complications are common in patients with myeloproliferative neoplasms (MPNs), with a subset developing acquired von Willebrand disease. Despite this association, a wide spectrum of von Willebrand factor (VWF) abnormalities are described, and the performance of modern assays remains unclear. ObjectivesTo comprehensively describe the pattern of VWF laboratory abnormalities in the MPN population. MethodsWe collected samples from 74 unselected clinic patients with MPNs to evaluate VWF quantitatively and qualitatively via multiple methods, correlating findings with a retrospective analysis of clinical bleeding data. VWF assays were performed on both ACL TOP (Instrumentation Laboratory) and Acustar (Instrumentation Laboratory) analyzers using HemosIL reagents (Instrumentation Laboratory), along with multimer analysis by gel electrophoresis. ResultsFunctional VWF measurements were not concordant between assays, with a median ACL TOP VWF glycoprotein IbR to antigen ratio (VWF:GPIbR/VWF:Ag) of 0.57 (IQR, 0.43-0.71) compared to a median Acustar VWF:GPIbR/VWF:Ag of 0.91 (IQR: 0.82-1.03;P < .001). The ACL TOP showed disproportionately lower results, with 73% of patients having a ratio <0.7. Despite this, no patient experienced loss of high-molecular-weight multimers by gel electrophoresis. An inverse relationship was observed between platelet count and functional ratios on both ACL TOP (R2 = 0.20; P < .001) and Acustar (R2 = 0.18; P = .0011) analyzers. While clinically significant bleeding events were relatively common (11% patients), there was no association with VWF assay abnormalities, and generally, an alternate cause(s) was identified. ConclusionDiscrepancies in functional VWF assays are common in patients with MPN, particularly by ACL TOP VWF:GPIbR. Based on our limited series, a VWF functional to an antigenic ratio of <0.7 (“type 2 pattern”) alone is poorly predictive of bleeding risk.

Comparison of von Willebrand factor platelet‐binding activity assays: ELISA overreads type 2B with loss of HMW multimers

BackgroundA number of new assays with different measuring principles are available to measure von Willebrand factor (VWF) glycoprotein Ib (GPIb)‐binding activity, but little is known about how these assays might behave differently for subtypes of von Willebrand disease (VWD). ObjectivesThe Comparison of Assays to Measure VWF Activity (COMPASS‐VWF) study was designed to compare all available VWF GPIb‐binding activity assays for VWF. We specifically searched for particular assay behavior differences. Patients/MethodsTo sort out random differences from systematic assay behavior deviations, all assays were performed in different laboratories on the same samples in a blinded fashion. Samples from 53 normal controls and 42 well‐characterized VWD patients were reanalyzed in this study to dissect assay‐specific discrepancies. ResultsNo assay behavior differences were found for 53 normal controls. For VWD patients, we found the following systematic assay behavior patterns: (a) All ELISA assays for VWF:GPIbR as well as VWF:GPIbM are insensitive to detect the low VWF activity of VWD type 2B patients with loss of high molecular weight multimers; (b) VWF:Ab assay reports higher activity for the p.V1665E mutation than all other assays; and (c) all ristocetin‐based assays (including VWF:RCo using fixed platelets) but the AcuStar assay report discrepantly low VWF activity for the p.P1467S polymorphism. No systematic assay‐specific difference was observed for either the particle agglutination VWF:GPIbM assay or the AcuStar assay using magnetic beads. ConclusionsDifferent assay principles may lead to discrepant results for certain VWD types or mutations. Therefore, a more extensive study for a large number of patients is needed to better characterize the incidence and relevance of such assay‐specific differences.

Effective hemostasis in children with Von Willebrand factor defects undergoing adenotonsillar procedures

Introduction Children with low von Willebrand factor (VWF) activity or type 1 von Willebrand disease (VWD) have increased risk of bleeding after adenotonsillar procedures and the optimal perioperative management to minimize bleeding is unknown. Aim To report the effectiveness and safety of an institutional protocol in minimizing postoperative bleeding in children with type 1 VWD or low VWF activity. Methods We conducted a retrospective chart review in children with type 1 VWD or low VWF activity treated via an institutional protocol that utilizes repeated doses of Desmopressin acetate (DDAVP, 1-deamino 8-D arginine- vasopressin) or VWF concentrate, brief hospitalization for observation and extended use of oral epsilon aminocaproic acid (EACA). Results From 2010 to 2017, 13 children underwent an adenotonsillar procedure and were treated with this protocol. Although 7.6% had minor immediate bleeding and 23% had minor delayed bleeding, no patients experienced major bleeding or required transfusion, additional surgery or other measures not specified by the protocol. Mild hyponatremia was observed in 80% of patients who received DDAVP. Conclusion Our institutional protocol specifying repeated dosing of DDAVP or VWF concentrate to sustain elevated VWF levels during periods of highest bleeding risk and extended use of EACA is effective at preventing major bleeding episodes after adenotonsillar procedures. However, this analysis raised safety concerns that prompted changes in the institutional protocol and highlight the need for further prospective studies to determine the optimal strategy for safely reducing bleeding complications in these patients.

Reduced Activity of von Willebrand Factor after Flow-Diverting Stent Implantation for Intracranial Aneurysms: A Link to Acquired von Willebrand Disease?

Vascular devices generating high shear stress can cause type 2A acquired von Willebrand disease, which is characterized by low von Willebrand factor activity accompanied by hemorrhagic complications. The braided mesh structure of flow-diverting stents with a relatively small strut size can create abnormally high shear stress while arterial blood flows through the stent struts into the aneurysm, and flow-diverting stent may be associated with reduced von Willebrand factor activity. Aneurysmal morphologic parameters and patient data were examined retrospectively among patients who had an unruptured intracranial aneurysm treated with a flow-diverting stent. The RISTOtest (test for whole blood ristocetin-induced platelet aggregation) for von Willebrand factor activity, as well as tests for aspirin and clopidogrel/prasugrel effectiveness, were performed immediately before the endovascular procedure and 24 hours later by multiple electrode aggregometry. A total of 39 patients with 56 aneurysms were recruited, and statistical analyses were performed in 32 patents with 49 aneurysms. Compared with the baseline values, von Willebrand factor activity was reduced in 16 patients but increased in 23 patients. Aneurysmal variables (eg, neck area, volume, volume-to-neck area ratio, size ratio, and morphologic index) clearly distinguished patients with reduced von Willebrand factor activity from those with nonreduced von Willebrand factor activity. The receiver operating characteristic curve showed that the morphologic index and volume had the highest discriminative power, with an area under the curve of 0.99. In high-volume/large-neck aneurysms, flow-diverting stent implantation can cause reduced von Willebrand factor activity, which may be linked causally to acquired von Willebrand disease.

The Discordance between Offsite to Onsite Testing for Von Willebrand Disease in Post-Menarchal Females: A Multi-Center Study

The Discordance between Offsite to Onsite Testing for Von Willebrand Disease in Post-Menarchal Females: A Multi-Center Study

Preoperative Detection of Low Von Willebrand Factor Activity and Operative Blood Loss in Pediatric Scoliosis Patients Undergoing Posterior Spinal Fusion

Purpose: Patients with von Willebrand disease (VWD), typically have von Willebrand Ristocetin cofactor activity (VWF: RCo) levels ≤30%. Patients with marginal levels 30-70 % don’t receive replacement therapy unless there is a bleeding history. Our program screens for VWF: RCo activity in advance of posterior spinal fusion (PSF) surgery. We hypothesized all patients with levels <70% are at higher bleeding risk when undergoing scoliosis repair. Design: this is a retrospective review of prospectively gathered data from a dedicated patient blood management program database. Methods: 169 scoliosis patients with preoperative VWF: RCo >70% were initially matched to 59 patients with activity ≤70%. Stratification was done at VWF: RCo levels >70 %, 61-70%, 51-60% and ≤50%, to examine blood loss. Matching was done by scoliosis type (idiopathic, neuromuscular, others), and operative difficulty. Both logistic regression and multivariate regression were used to examine the various levels. Results: Patients with VWF: RCo >70 % compared to those with ≤70% had similar demographics, blood loss, and transfusion rates. On stratification, blood loss/segment fused with VWF: RCo levels 70%, p = 0.044. Multivariate regression revealed compared to other levels, those patients with VWF: RCo levels ≤60 % were most likely to have higher blood loss even on controlling for potential confounders (p < 0.005). Sixteen patients with levels <50% had significant bleeding despite factor replacement in 15. Conclusion: Layered multivariate analysis showed that patients with VWF: RCo levels ≤ 60% carried higher risk of operative bleeding/ level fused. Prospective therapeutic studies are much needed.Purpose: Patients with von Willebrand disease (VWD), typically have von Willebrand Ristocetin cofactor activity (VWF: RCo) levels ≤30%. Patients with marginal levels 30-70 % don’t receive replacement therapy unless there is a bleeding history. Our program screens for VWF: RCo activity in advance of posterior spinal fusion (PSF) surgery. We hypothesized all patients with levels <70% are at higher bleeding risk when undergoing scoliosis repair. Design: this is a retrospective review of prospectively gathered data from a dedicated patient blood management program database. Methods: 169 scoliosis patients with preoperative VWF: RCo >70% were initially matched to 59 patients with activity ≤70%. Stratification was done at VWF: RCo levels >70 %, 61-70%, 51-60% and ≤50%, to examine blood loss. Matching was done by scoliosis type (idiopathic, neuromuscular, others), and operative difficulty. Both logistic regression and multivariate regression were used to examine the various levels. Results: Patients with VWF: RCo >70 % compared to those with ≤70% had similar demographics, blood loss, and transfusion rates. On stratification, blood loss/segment fused with VWF: RCo levels 70%, p = 0.044. Multivariate regression revealed compared to other levels, those patients with VWF: RCo levels ≤60 % were most likely to have higher blood loss even on controlling for potential confounders (p < 0.005). Sixteen patients with levels <50% had significant bleeding despite factor replacement in 15. Conclusion: Layered multivariate analysis showed that patients with VWF: RCo levels ≤ 60% carried higher risk of operative bleeding/ level fused. Prospective therapeutic studies are much needed.

Concordance of DDAVP Response in Siblings with Von Willebrand Disease or Hemophilia a

Background: Von Willebrand disease (VWD) is the most common congenital bleeding disorder, affecting 1 in 5,000 individuals. Von Willebrand factor (VWF) is an important component in platelet binding to form a primary hemostatic plug. Individuals with VWD have difficulty forming a platelet plug and thus have symptoms such as spontaneous bleeding from mucous membranes, epistaxis, excessive bleeding from wounds, and menorrhagia.DDAVP is a synthetic derivative of the antidiuretic hormone, vasopressin, and is currently used as a mainstay of therapy in VWD. The mechanism of action is thought to be a release of VWF from endothelial cell Weibel-Palade bodies through DDAVP's agonist effect on vasopressin V2 receptors, which, in effect increases plasma concentrations of VWF. Not every patient will respond to treatment, so DDAVP challenge tests are recommended in children with newly diagnosed VWD to identify responders in whom DDAVP may be used for the prevention or treatment of bleeding.Von Willebrand disease is inherited in an autosomal dominant pattern, so multiple members are commonly affected within a family. Siblings are likely to carry the same mutation and may or may not have a similar response to treatment. Our study is aimed at addressing the question of whether siblings of responders or non-responders in DDAVP trials have concordant results and therefore do not need DDAVP trial.Methods: With Human Investigation Committee and IRB approval we performed a retrospective chart review of patients who have undergone DDAVP trial at Children's Hospital of Michigan. Levels of VWF were measured at baseline and then at one, two and four hours. A positive response was defined as an increase in VWF of twofold over baseline, to at least 50 IU/dL. Results were then compared among sibling pairs to see if there was a similar response.Results: We examined 57 patients and had 2 related pairs. Before administering DDAVP, the average baseline of VWF activity, VWF antigen, and Factor VIII were 62.71, 60.95, and 73.58 respectively. 55 patients showed full response to trial with DDAVP. In each of our 2 sibling pairs, both family members showed full response.Discussion: Performing DDAVP trials in every child with symptomatic bleeding is not only costly, but also time consuming. In addition, the IV line placements, infusions, and blood draws involved can be a stressful and painful experience for the child. In a study by Archer et al, later published in BJH (2015), they tested response to DDAVP trial in children with low VWF, and had a 95% response rate. They concluded that, given the high response rate, the use of DDAVP challenge tests in pediatric patients with low VWF should be reduced.Conclusion: In our study, we found that in both sets of siblings, each member showed full response to trial with DDAVP. If there is a genetic correlation to whether or not one responds, these siblings may have benefited from not having to each undergo testing. We would like to further our investigation with a larger data set, and plan to look at a large multicenter cohort. Additionally, although not a primary endpoint of our study our data confirm the findings from the study by Archer et. al.. All of our patients with low VWF activity (>30%<50%) responded to DDAVP and DDAVP trials may not be needed in this group. DisclosuresNo relevant conflicts of interest to declare.

Hemostatic Abnormalities in Young Females with Heavy Menstrual Bleeding

ObjectiveTo study the prevalence of hemostatic abnormalities, including bleeding disorders and risk factors, in young females referred to a multidisciplinary clinic for evaluation of heavy menstrual bleeding (HMB). MethodsRetrospective chart review was undertaken for 131 post-menarchal girls with HMB, 7 to 17 years of age, enrolled in the institutional ‘Menorrhagia Data Registry’ protocol. The diagnostic approach included: (1) complete blood count, prothrombin time, partial thromboplastin time, fibrinogen, von Willebrand panel (2) platelet aggregometry, specific clotting factor assay, fibrinolytic pathway analysis, and factor XIII level as needed. The prevalence of hemostatic abnormalities and the prognostic significance of clinical variables associated with hemostatic abnormalities in young girls with HMB were evaluated. ResultsA hemostatic abnormality was identified in 69 (53%) young girls with HMB. Of these, 27 (21%) had an underlying bleeding disorder and 42 (32%) had a risk factor for bleeding, namely low von Willebrand factor activity. A larger number of girls with underlying bleeding disorder had personal history of other bleeding symptoms (48% vs 31%) and bleeding after surgical or dental procedure (25% vs 8%) when compared to females without hemostatic abnormality. Furthermore, girls with risk factor for bleeding (low vWF activity) were more likely to have bleeding after surgical or dental procedure (15% vs 8%) and family history of bleeding (79% vs 60%) than patients without hemostatic abnormality. ConclusionsThere is high prevalence of hemostatic abnormalities, including bleeding disorders and risk factors, in young girls with HMB. These findings support comprehensive and systematic hemostatic evaluation in this group of patients.

Technological advances in diagnostic testing for von Willebrand disease: new approaches and challenges.

Diagnostic tests for von Willebrand disease (VWD) are important for the assessment of VWD, which is a commonly encountered bleeding disorder worldwide. Technical innovations have been applied to improve the precision and lower limit of detection of von Willebrand factor (VWF) assays, including the ristocetin cofactor activity assay (VWF:RCo) that uses the antibiotic ristocetin to induce plasma VWF binding to glycoprotein (GP) IbIXV on target platelets. VWF-collagen-binding assays, depending on the type of collagen used, can improve the detection of forms of VWD with high molecular weight VWF multimer loss, although the best method is debatable. A number of innovations have been applied to VWF:RCo (which is commonly performed on an aggregometer), including replacing the target platelets with immobilized GPIbα, and quantification by an enzyme-linked immunosorbent assay (ELISA), immunoturbidimetric, or chemiluminescent end-point. Some common polymorphisms in the VWF gene that do not cause bleeding are associated with falsely low VWF activity by ristocetin-dependent methods. To overcome the need for ristocetin, some new VWF activity assays use gain-of-function GPIbα mutants that bind VWF without the need for ristocetin, with an improved precision and lower limit of detection than measuring VWF:RCo by aggregometry. ELISA of VWF binding to mutated GPIbα shows promise as a method to identify gain-of-function defects from type 2B VWD. The performance characteristics of many new VWF activity assays suggest that the detection of VWD, and monitoring of VWD therapy, by clinical laboratories could be improved through adopting newer generation VWF assays.

Platelet-Type von Willebrand Disease: New Insights into the Molecular Pathophysiology of a Unique Platelet Defect

Compared with coagulation factor defects, little attention is given to defects of platelet function as causes of rare bleeding disorders. Platelet-type von Willebrand disease (PT-VWD) is an autosomal dominant bleeding disorder and is unique among platelet disorders because it is characterized by platelet hyperresponsiveness rather than decreased function. The disease is caused by gain-of-function mutations in the platelet GP1BA gene, which codes for the platelet von Willebrand factor (VWF) receptor, GPIbα. Only five mutations (four missense and one deletion) have so far been reported. Affected patients suffer from mild to moderate mucocutaneous bleeding, low VWF activity compared with antigen, decreased high-molecular-weight VWF multimers, variable degree of thrombocytopenia and typically platelet aggregation in response to low concentrations of ristocetin. All reported PT-VWD missense mutations occur within the R-loop of GPIbα and it was speculated that the introduction of short branched chain mutations such as Val in PT-VWD stabilized the extended β-hairpin. Examination of this theory by surveying all the available GPIbα structures showed that a distinct conformation predominates for the R-loop when GPIbα is not bound to VWF-A1 and this provides the framework of a new hypothesis for the molecular basis of PT-VWD. Worldwide efforts to improve diagnosis of PT-VWD continue, and international systematic studies are required to further our understanding of the phenotype and the influence of the hyperresponsive GPIbα beyond hemostasis.

Identification and Functional Analysis of a Novel von Willebrand Factor Mutation in a Family with Type 2A von Willebrand Disease

von Willebrand factor (VWF) is essential for normal hemostasis. VWF gene mutations cause the hemorrhagic von Willebrand disease (VWD). In this study, a 9-year-old boy was diagnosed as type 2A VWD, based on a history of abnormal bleeding, low plasma VWF antigen and activity, low plasma factor VIII activity, and lack of plasma high-molecular-weight (HMW) VWF multimers. Sequencing analysis detected a 6-bp deletion in exon 28 of his VWF gene, which created a mutant lacking D1529V1530 residues in VWF A2 domain. This mutation also existed in his family members with abnormal bleedings but not in >60 normal controls. In transfected HEK293 cells, recombinant VWF ΔD1529V1530 protein had markedly reduced levels in the conditioned medium (42±4% of wild-type (WT) VWF, p<0.01). The mutant VWF in the medium had less HMW multimers. In contrast, the intracellular levels of the mutant VWF in the transfected cells were significantly higher than that of WT (174±29%, p<0.05), indicating intracellular retention of the mutant VWF. In co-transfection experiments, the mutant reduced WT VWF secretion from the cells. By immunofluorescence staining, the retention of the mutant VWF was identified within the endoplasmic reticulum (ER). Together, we identified a unique VWF mutation responsible for the bleeding phenotype in a patient family with type 2A VWD. The mutation impaired VWF trafficking through the ER, thereby preventing VWF secretion from the cells. Our results illustrate the diversity of VWF gene mutations, which contributes to the wide spectrum of VWD.

Evaluation of the new INNOVANCE® PFA P2Y cartridge in patients with impaired primary haemostasis

Recently, the INNOVANCE® PFA P2Y (P2Y) cartridge of the PFA-100® system (Siemens Healthcare Diagnostics, Marburg, Germany) has been developed for the monitoring of adenosine diphosphate (ADP) P2Y12 receptor inhibition in patients under dual antiplatelet therapy. The aim of this study was to evaluate the influence of pre-existing defects in primary haemostasis on the P2Y cartridge independent from specific antiplatelet medication. Therefore, the closure time (CT) of the P2Y cartridge was measured in a cohort of 176 patients with assumed bleeding disorders and compared with the results of established methods for the assessment of primary haemostasis. Von Willebrand disease (VWD) was found in 25 patients (14%). The detection rate of the P2Y cartridge regarding VWD was 64% and lower compared to the two conventional cartridges (collagen/epinephrine cartridge, CEPI, 80%; collagen/ADP cartridge, CADP, 76%). In the subgroup of VWD patients with VWF:RCo < 60 IU/dL (n = 22), the correlation analysis and the inter-rater agreement revealed only limited accordance with the two established cartridges. The correlation with the CADP cartridge (Cr = 0.767, R2 = 0.461; Kappa = 0.41) was higher than the correlation with the CEPI cartridge. Except for severe forms, platelet function disorders (9 patients, 5%) did not prolong the CT of the P2Y cartridge. Interestingly, the P2Y cartridge was less interference-prone to unspecific medications (23 patients, 13%). As the main conclusion, it must be taken into account that low von Willebrand factor activity can significantly influence the CTs of the P2Y cartridge when using it for the monitoring of antiplatelet therapy.

Platelet Dysfunction in Outpatients With Left Ventricular Assist Devices

Thromboembolic and bleeding complications in outpatients with a left ventricular assist device are common and can be detrimental. A meticulous balance between anticoagulant and procoagulant factors is therefore crucial. However, in contrast to routinely performed plasmatic coagulation tests, platelet function is hardly ever monitored although recent reports indicated platelet dysfunction. We therefore differentially evaluated platelet function with four commonly used point-of-care devices. In a cross-sectional design platelet function was assessed in 12 outpatients and 12 healthy matched volunteers using thrombelastography platelet mapping, thromboelastometry, platelet function analyzer, and a new whole blood aggregometer (Multiplate). Phenprocoumon produced an international normalized ratio of 3.5. It was associated with a twofold prolongation in the thromboelastometry clotting time (p < 0.001). Platelet function under high shear was severely compromised: collagen adenosine diphosphate closure times were 2.5-fold longer in patients than in volunteers (p < 0.001), and 50% of patients had maximal collagen adenosine diphosphate closure time values. Although antigen levels of von Willebrand factor were 80% higher in patients (p < 0.001), von Willebrand factor-ristocetin was subnormal in 5 of 12 patients. Ristocetin-induced aggregation was also threefold higher in volunteers (p < 0.001), indicating an additional functional defect of platelets affecting the glycoprotein Ib-von Willebrand factor axis. The von Willebrand factor multimer pattern in patients also appeared abnormal. Multimodal antiplatelet monitoring showed markedly impaired platelet function in patients with a left ventricular assist device. Platelet dysfunction under high shear rates and abnormal ristocetin-induced aggregation is only partly attributable to low von Willebrand factor activity. These findings resemble the acquired von Willebrand syndrome that is associated with microaggregate formation and enhanced bleeding.

A Progressive Acquired Von Willebrand Factor Inhibitor in a Patient with Type 1 Von Willebrand's Disease, Persistent Antiphospholipid Antibodies and An IgA Paraprotein

Acquired von Willebrand's disease (AVWD) is a rare bleeding disorder with similar clinical and laboratory findings to the inherited disorder. It can be caused by specific or non-specific antibodies, adsorption of von Willebrand factor (VWF) onto malignant cell clones, hypothyroidism or loss of high molecular weight multimers under conditions of high sheer stress. AVWD is commonly diagnosed using standard laboratory tests for inherited VWD in the absence of a family history of bleeding. In this abstract we present an unusual case of development of antibodies in a 76 year old white caucasian lady with documented desmopressin responsive Type 1 VWD and a family history of VWD. Her baseline laboratory parameters were VWF: Ag of 26.6 IU/dL (RR 45–160 IU/dL), Factor VIII:C of 52.6 IU/dL (RR 50–200 IU/dL) and normal VWF multimer distribution. She presented with undetectable VWF:RCo, VWF:CB 2.9 IU/dL, VWF:Ag 8.2 IU/dL, FVIII:C 8.4 IU/dL and unmeasurable PFA-100 closure times during routine work-up prior to planned elective surgery. There had been no significant change in her clinical symptomatology. The lupus anticoagulant and moderately elevated IgM anticardiolipin antibodies which had been detected three years previously remained positive and a Bethesda assay for FVIII inhibitor was negative. Her rheumatoid factor, antinuclear antibody and double stranded DNA antibody tests were negative. She was extensively investigated for an underlying malignancy but the only positive finding was that of an IgG kappa paraprotein band. The IgG level was 7.5 g/L (RR 6–16 g/L) without any evidence of immune paresis. Assay for VWF:RCo inhibitor on a 1:1 mixture of patient and normal plasma after 5 minute incubation at 37°C was negative. The patient was infused with VWF concentrate Haemate 8000 RCo units and serial assays of VWF:RCo, VWF:Ag and FVIII:C were undertaken. At 10 minutes post-infusion the levels were 173.0, 161.6 and 70.3 IU/dL respectively and 88.2, 131.1 and 39.8 IU/dL respectively at 20 minutes. The VWF:RCo dropped to 10.0 IU/dL by 4 hours whereas the VWF:Ag was 43.1 IU/dL at that point and 27.2 IU/dL at 8 hours, when the VWF:RCo had reduced further to 6.8 IU/dL. The FVIII:C continued to fall until it levelled off at 27.5 IU/dL at 2 hours. The VWF:RCo inhibitor assay was repeated on an incubated 1:1 mixture of patient and normal plasma. The normal plasma was manipulated to have a value at the start of the assay of 130.0 IU/dL once mixed with patient plasma, which fell to 92.0, 87.0 and 78.0 IU/dL after 30 minutes, 4 hours and 18 hours incubation respectively, revealing a progressive inhibitor of VWF:RCo activity. The antibody demonstrated is likely to be an acquired autoantibody rather than an antibody to previously infused von Willebrand factor concentrate as the pre-infusion VWF activity and antigen levels in the patient were undetectable. Also, the additional presence of antiphospholipid antibodies may indicate the inherent propensity of the patient to produce autoantibodies. Further, the additional presence of an IgA paraprotein band may also have contributed to the low VWF activity levels. It is interesting to speculate on the multifactorial nature of the pathogenic mechanism of development of multiple auto-antibodies in this patient. AVWD associated with paraproteinemia is well described. However, in this case the AVWD and paraprotenemia developed on a background of lifelong history of inherited VWD. To our knowledge this is the first reported case of development of acquired antibodies in a patient with pre-existing inherited VWD. Her forthcoming surgery will provide further challenges for management.

Thrombin-generating capacity in patients with von Willebrand's disease

on Willebrand's disease (VWD) is the most common hereditary bleeding disorder. Its severity can be classified on the basis of von Willebrand factor (VWF) and factor VIII (FVIII) plasma levels and according to the clinical relevance of bleeding episodes. However, patients with very low VWF activity may exhibit a mild bleeding tendency. The basis for this heterogeneous clinical expression of the deficit is still poorly understood. We investigated the relationship between thrombin generation and levels of factor VIII, VWF and clinical bleeding tendency. Thrombin generation was measured in platelet-rich (PRP) and platelet-poor plasma (PPP) from 53 patients with VWD. We observed a statistically significant higher risk of bleeding in patients with a low thrombin peak in PRP (OR=14.5; 95% CI=5-41.3). Similar results were found in PPP (OR=8.71; 95% CI=3.4-22.3). Two parameters of the thrombin generation curve, peak height and thrombin generation speed (slope), correlated significantly with VWF:RCo and FVIII levels both in PPP and in PRP. Regression analysis showed that thrombin generation was mainly dependent on plasma FVIII activity. Our results suggest that the thrombin generation test, in combination with routine FVIII and VWF measurements, could be of interest in the assessment of the individual bleeding risk in patients with VWD.