Von Willebrand Factor Antigen Concentration Research Articles

A Fluorescence Cross-Correlation-Spectroscopy-Based Immunoassay for Rapid, Selective, and Accurate Protein Sizing in Human Plasma, Applied to the von Willebrand Factor.

Multimeric abnormalities in plasma von Willebrand factor (VWF) cause bleeding or clotting disorders. Electrophoretic analysis of multimers is used to detect such abnormalities but is qualitative, slow, and difficult to standardize. Fluorescence correlation spectroscopy (FCS) is a good alternative but is affected by low selectivity and concentration bias. Here, we report the development of a homogeneous immunoassay based on dual-color fluorescence cross-correlation spectroscopy (FCCS) that overcomes these challenges. By performing a mild denaturation treatment followed by reacting with polyclonal antibodies, the concentration bias was drastically reduced. The use of a dual antibody assay improved selectivity. Diffusion times of immunolabeled VWF were measured with FCCS and standardized relative to calibrator measurements. The assay measures size changes in VWF using 1 μL of plasma and less than 10 ng of antibody per measurement and was validated over a 16-fold range of VWF antigen concentration (VWF:Ag), with a sensitivity of VWF:Ag 0.8%. Concentration bias and imprecision were less than 10%. Measurements were unaffected by hemolytic, icteric, or lipemic interference. Strong correlations were obtained with reference densitometric readouts (0.97 for calibrators, 0.85 for clinical samples), and significant differences were found between normal (n = 10), type 2A (n = 5), and type 2B (n = 5) von Willebrand's disease and acquired thrombotic thrombocytopenic purpura (n = 10) samples (p < 0.01). This FCCS based immunoassay accurately and selectively determines changes in the multimeric status of plasma VWF and may be used as a simpler, faster, and a standardizable alternative for multimer analysis, following further clinical validation in larger cohorts.

Endothelial dysfunction in patients with various forms of congenital epidermolysis bullosa

Introduction. The endothelial system is an important component of vascular-platelet hemostasis, capable of actively responding to mechanical and inflammatory agents. Patients with congenital epidermolysis bullosa are prone to mechanical damage to the skin and the development of a chronic inflammatory syndrome with a high probability of endothelial dysfunction.The study objective was to assess the state of the endothelial system and to reveal the dependence of endothelial dysfunction on the form of epidermolysis bullosa.Methods and materials. The study used venous blood of 57 patients (27 men and 30 women) with congenital epidermolysis bullosa. In patients with simple and dystrophic forms of epidermolysis bullosa, the platelet count, P-selectin, fibrinogen, albumin, C-reactive protein, von Willebrand factor antigen concentration, and factor VIII activity were determined.Results. Comparative results of endothelial dysfunction depending on the form of epidermolysis bullosa were represented and endothelial dysfunction’s dependence on the concentration of albumin, C-reactive protein, and platelet count was determined.Conclusions. In patients with a dystrophic form of epidermolysis bullosa, endothelial dysfunction is accompanied by an increase in the expression of P-selectin, factor VIII activity, and the concentration of von Willebrand factor antigen. Chronic inflammation and impaired nutritional status with a decrease in albumin contribute to the development of endothelial dysfunction.

Associations between the von Willebrand Factor-ADAMTS13 Axis, Complement Activation, and COVID-19 Severity and Mortality.

Background Endothelial and complement activation were both associated with immunothrombosis, a key determinant of COVID-19 severity, but their interrelation has not yet been investigated. Objectives We aimed to determine von Willebrand factor (VWF) antigen (VWF:Ag) concentration, VWF collagen binding activity (VWF:CBA), a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) activity (ADAMTS13:Ac), and their ratios in hospitalized COVID-19 patients, and to investigate how these parameters and their constellation with complement activation relate to disease severity and in-hospital mortality in COVID-19. Methods Samples of 102 hospitalized patients with polymerase chain reaction-confirmed severe acute respiratory syndrome coronavirus 2 positivity were included in our observational cohort study. Patients were stratified according to the peak severity of COVID-19 disease in agreement with the World Health Organization ordinal scale. Twenty-six convalescent plasma donors with previous COVID-19 disease formed the control group. VWF:Ag concentration and VWF:CBA were determined by enzyme-linked immunosorbent assay (ELISA); ADAMTS13:Ac was determined by fluorescence resonance energy transfer. Complement C3 and C3a were measured by turbidimetry and ELISA, respectively. Clinical covariates and markers of inflammation were extracted from hospital records. Results VWF:Ag and VWF:CBA were elevated in all groups of hospitalized COVID-19 patients and increased in parallel with disease severity. ADAMTS13:Ac was decreased in patients with severe COVID-19, with the lowest values in nonsurvivors. High (> 300%) VWF:Ag concentrations or decreased (< 67%) ADAMTS13:Ac were associated with higher risk of severe COVID-19 disease or in-hospital mortality. The concomitant presence of decreased ADAMTS13:Ac and increased C3a/C3 ratio—indicating complement overactivation and consumption—was a strong independent predictor of in-hospital mortality. Conclusion Our results suggest that an interaction between the VWF-ADAMTS13 axis and complement overactivation and consumption plays an important role in the pathogenesis of COVID-19.

Long-Term Safety and Efficacy of Caplacizumab for Acquired Thrombotic Thrombocytopenic Purpura (aTTP): The Post-HERCULES Study

Long-Term Safety and Efficacy of Caplacizumab for Acquired Thrombotic Thrombocytopenic Purpura (aTTP): The Post-HERCULES Study

Thrombosis and Von Willebrand Factor in Chuvash Polycythemia

Background: In Chuvash polycythemia (CP), homozygous germline VHLR200W results in augmented hypoxia-sensing, elevated erythropoietin and hemoglobin, and increased morbidity and mortality from venous and arterial thromboses.1 In CP patients and controls from Russia's Chuvash Republic, the probability of new thrombosis in CP increased with age, smoking, and higher expression of THBS1, the gene encoding thrombospondin-1.2 In mice, hypoxia leads to upregulation of THBS1 through HIF-23 and to upregulation of VWF .4 THBS1 reportedly regulates the size of circulating von Willebrand Factor (VWF) multimers5 through inhibiting proteolytic cleavage of VWF by ADAMTS13.6 We hypothesized that upregulation of THBS1 in CP may be a risk for thrombosis through an effect on ADAMTS13 and VWF.Methods: We enrolled into an observational study 155 patients with CP and 154 controls matched by age, sex and place of residence. Written informed consent was obtained from all subjects according to the Declaration of Helsinki. We genotyped for VHLR200W, measured baseline plasma THBS-1 concentrations2 and followed the subjects for a median of 9.4 years. Here, we report results for determining baseline circulating levels of ADAMTS13 antigen, activity and specific activity and of VWF antigen and differential multimers in up to 57 CP patients and 30 controls.Results: CP subjects had higher hemoglobin and erythropoietin concentrations and lower white blood cell and platelet counts (Table 1). They were also more likely to be current smokers. There was a trend to higher THBS-1 concentrations in the CP patients (p=0.084), which was significant after adjusting for platelet count (P=0.016). ADAMTS13 and VWF antigen levels did not differ between CP patients and controls but ADAMTS13 activity and especially specific activity were lower in CP. Plasma THBS-1 concentration correlated positively with ADAMTS13 antigen concentration (r=0.358, P=0.001) but negatively with specific activity (r=-0.363, P=0.001) (Figure 1). Eight (14.0%) CP patients (aged 27-76) years had a history of thrombosis (Table 1). The mean serum VWF antigen concentration (P=0.001) and differential VWF multimer size (P=0.090) were higher in CP patients with a history of thrombosis (Figure 2). During the prospective follow-up period, 10 CP patients (17.5%) experienced a new thrombosis at a median age of 46 (range 26-70) years. Three patients also experienced an additional thrombosis for a total of 13 new thromboses: myocardial infarction (n=5), stroke (n=3), splanchnic thrombosis (n=2), deep vein thrombosis (n=2), pulmonary embolism (n=1). Baseline serum VWF antigen levels (P=0.019) and VWF multimer size (P=0.099) were higher in subjects who developed a new thrombosis during follow-up (Figure 3), and these relationships persisted after adjusting for smoking history.Discussion: THBS1 is an adhesive glycoprotein that mediates cell-to-cell and cell-to-matrix interactions and facilitates platelet aggregation.7 In mice, platelet-derived THBS1 modulated arterial thrombosis only in the presence of VWF.8 Our present findings suggest that CP subjects have lower ADAMTS13 specific activity than controls and that this lower activity may be related to higher plasma THBS1 concentrations. Lower ADAMTS13 specific activity suggests the presence of an inhibitor or partial inactivation of the protease. Furthermore, higher VWF antigen and multimer size in CP patients is associated with a past history of thrombosis and a greater risk for new thrombosis in the future. More broadly, our findings suggest a possible implication of VWF in thrombosis of conditions associated with an up-regulated hypoxic response. Further studies may identify new pathways of prevention and treatment with broad applicability.

Platelet function in dogs with chronic liver disease.

To assess platelet function, buccal mucosal bleeding time and plasma von Willebrand factor concentration in dogs with chronic inflammatory and/or fibrotic liver disease and to compare results with those obtained in healthy dogs. Preliminary study including 18 dogs with chronic inflammatory and/or fibrotic liver disease undergoing liver biopsy and 18 healthy age-matched control dogs. Platelet function was assessed by measuring closure time with the PFA-100® analyser using adenosine diphosphate (ADP) as an agonist. Buccal mucosal bleeding time, closure time and plasma von Willebrand factor antigen were measured in dogs in both groups. After undergoing ultrasound-guided needle biopsy, dogs were monitored for haemorrhage to determine if there was an association of any measurement with post-biopsy bleeding. The closure time was not different between the liver disease group (median 76.3; range 53 to 118.5seconds) and control group (72.8; 57 to 89.5seconds). The buccal mucosal bleeding time was longer in the liver disease group (median 138; range 95 to 229 seconds) than the control group (103; 63 to 200 seconds). The plasma von Willebrand factor antigen concentration was not different between the liver disease group (median 203; range 109 to 351%) and control group (165.5; 63 to 246%). In this study, dogs with chronic necroinflammatory and/or fibrotic liver disease did not have overt, clinically relevant derangements in platelet function as assessed by buccal mucosal bleeding time, closure time and von Willebrand factor analysis. In addition, none of the dogs undergoing percutaneous ultrasound-guided biopsy in the study exhibited bleeding complications post-biopsy procedure.

Endotheliopathy in COVID-19-associated coagulopathy: evidence from a single-centre, cross-sectional study

SummaryBackgroundAn important feature of severe acute respiratory syndrome coronavirus 2 pathogenesis is COVID-19-associated coagulopathy, characterised by increased thrombotic and microvascular complications. Previous studies have suggested a role for endothelial cell injury in COVID-19-associated coagulopathy. To determine whether endotheliopathy is involved in COVID-19-associated coagulopathy pathogenesis, we assessed markers of endothelial cell and platelet activation in critically and non-critically ill patients admitted to the hospital with COVID-19.MethodsIn this single-centre cross-sectional study, hospitalised adult (≥18 years) patients with laboratory-confirmed COVID-19 were identified in the medical intensive care unit (ICU) or a specialised non-ICU COVID-19 floor in our hospital. Asymptomatic, non-hospitalised controls were recruited as a comparator group for biomarkers that did not have a reference range. We assessed markers of endothelial cell and platelet activation, including von Willebrand Factor (VWF) antigen, soluble thrombomodulin, soluble P-selectin, and soluble CD40 ligand, as well as coagulation factors, endogenous anticoagulants, and fibrinolytic enzymes. We compared the level of each marker in ICU patients, non-ICU patients, and controls, where applicable. We assessed correlations between these laboratory results with clinical outcomes, including hospital discharge and mortality. Kaplan–Meier analysis was used to further explore the association between biochemical markers and survival.Findings68 patients with COVID-19 were included in the study from April 13 to April 24, 2020, including 48 ICU and 20 non-ICU patients, as well as 13 non-hospitalised, asymptomatic controls. Markers of endothelial cell and platelet activation were significantly elevated in ICU patients compared with non-ICU patients, including VWF antigen (mean 565% [SD 199] in ICU patients vs 278% [133] in non-ICU patients; p<0·0001) and soluble P-selectin (15·9 ng/mL [4·8] vs 11·2 ng/mL [3·1]; p=0·0014). VWF antigen concentrations were also elevated above the normal range in 16 (80%) of 20 non-ICU patients. We found mortality to be significantly correlated with VWF antigen (r = 0·38; p=0·0022) and soluble thrombomodulin (r = 0·38; p=0·0078) among all patients. In all patients, soluble thrombomodulin concentrations greater than 3·26 ng/mL were associated with lower rates of hospital discharge (22 [88%] of 25 patients with low concentrations vs 13 [52%] of 25 patients with high concentrations; p=0·0050) and lower likelihood of survival on Kaplan–Meier analysis (hazard ratio 5·9, 95% CI 1·9–18·4; p=0·0087).InterpretationOur findings show that endotheliopathy is present in COVID-19 and is likely to be associated with critical illness and death. Early identification of endotheliopathy and strategies to mitigate its progression might improve outcomes in COVID-19.FundingThis work was supported by a gift donation from Jack Levin to the Benign Hematology programme at Yale, and the National Institutes of Health.

Desialylation of platelets induced by Von Willebrand Factor is a novel mechanism of platelet clearance in dengue.

Thrombocytopenia and platelet dysfunction are commonly observed in patients with dengue virus (DENV) infection and may contribute to complications such as bleeding and plasma leakage. The etiology of dengue-associated thrombocytopenia is multifactorial and includes increased platelet clearance. The binding of the coagulation protein von Willebrand factor (VWF) to the platelet membrane and removal of sialic acid (desialylation) are two well-known mechanisms of platelet clearance, but whether these conditions also contribute to thrombocytopenia in dengue infection is unknown. In two observational cohort studies in Bandung and Jepara, Indonesia, we show that adult patients with dengue not only had higher plasma concentrations of plasma VWF antigen and active VWF, but that circulating platelets had also bound more VWF to their membrane. The amount of platelet-VWF binding correlated well with platelet count. Furthermore, sialic acid levels in dengue patients were significantly reduced as assessed by the binding of Sambucus nigra lectin (SNA) and Maackia amurensis lectin II (MAL-II) to platelets. Sialic acid on the platelet membrane is neuraminidase-labile, but dengue virus has no known neuraminidase activity. Indeed, no detectable activity of neuraminidase was present in plasma of dengue patients and no desialylation was found of plasma transferrin. Platelet sialylation was also not altered by in vitro exposure of platelets to DENV nonstructural protein 1 or cultured DENV. In contrast, induction of binding of VWF to glycoprotein 1b on platelets using the VWF-activating protein ristocetin resulted in the removal of platelet sialic acid by translocation of platelet neuraminidase to the platelet surface. The neuraminidase inhibitor oseltamivir reduced VWF-induced platelet desialylation. Our data demonstrate that excessive binding of VWF to platelets in dengue results in neuraminidase-mediated platelet desialylation and platelet clearance. Oseltamivir might be a novel treatment option for severe thrombocytopenia in dengue infection.

Is there any Relationship between Rh(D) Blood Group and Von Willebrand Factor Antigen Concentration?

Is there any Relationship between Rh(D) Blood Group and Von Willebrand Factor Antigen Concentration?

Abstract 17665: Complementary Role of Von Willebrand Factor Indices to Brain Natriuretic Peptide in Hypertrophic Cardiomyopathy

Introduction: In hypertrophic cardiomyopathy (HCM), brain natriuretic peptide (BNP) has been weakly associated with septal thickness, diastolic function parameters, resting left ventricular outflow tract gradient ([[Unable to Display Character: &amp;#8710;]]P), and more strongly associated with prognosis. Von Willebrand factor activity is known to be altered in HCM, and acquired bleeding may occur in up to ¼ of patients. Hypothesis: We hypothesized that indices of von Willebrand factor (VWF) activity would be more strongly related to [[Unable to Display Character: &amp;#8710;]]P than BNP. Methods: We compared BNP and three independent measures of VWF function to echo/Doppler parameters in 84 HCM patients. Results: In obstructive (resting [[Unable to Display Character: &amp;#8710;]]P ≥30 mm Hg), n-58 versus labile HCM (resting [[Unable to Display Character: &amp;#8710;]]P &lt;30 mm Hg, Valsalva [[Unable to Display Character: &amp;#8710;]]P ≥30 mm Hg), n=28, VWF multimers were abnormal in 90% versus 52% (p=0.0005), VWF activity to antigen ratio was markedly lower, 0.76±0.09 vs 0.89±0.16, p&lt;0.0001, and PFA markedly prolonged, 207±75 versus 129±61 seconds (p&lt;0.0001), while BNP was moderately higher, 331±273 versus176±163 pg/ml, p=0.007. BNP correlated (Spearman rho, ρ), most strongly with echocardiographic E/e’ (ρ=0.51, p&lt;0.001) and left atrial volume (ρ=0.34, p=0.003) but not peak gradient, [[Unable to Display Character: &amp;#8710;]]P, (ρ=0.13, NS), while BNP normalized for age and gender was weakly associated with [[Unable to Display Character: &amp;#8710;]]P, ρ=0.26,p=0.02 and powerfully associated with septal thickness (ρ=0.50, p&lt;0.001), and left ventricular mass index (ρ=0.43, p&lt;0.001). In contrast, quantitative VWF activity measures correlated strongly with [[Unable to Display Character: &amp;#8710;]]P, VWF activity/antigen (ρ=-0.59, p&lt;0.0001), and PFA (ρ=0.51, p&lt;0.0001). In HCM patients with bleeding (n=31), VWF antigen level was higher than in those without bleeding suggesting that the combination of elevated total VWF antigen and absent high molecular weight multimers may be involved in the causation of bleeding. Conclusion: Our data suggest that BNP elevations are associated most strongly with E/e’, left atrial volume, septal thickness, and left ventricular mass, while VWF activity indices more strongly reflect [[Unable to Display Character: &amp;#8710;]]P, and may thus have a complementary role in assessing therapeutic responses and prognosis. Loss of high molecular weight VWF multimers and elevated total VWF antigen concentration may be a novel marker of bleeding risk from acquired von Willebrand syndrome in HCM.

SEPTAL MYECTOMY IS PREFERRED OVER SEPTAL ABLATION OR MEDICAL THERAPY TO CORRECT VON WILLEBRAND FACTOR ABNORMALITIES IN HYPERTROPHIC CARDIOMYOPATHY

Surgical septal myectomy is referred to as the gold standard for relief of functional class III and IV symptoms associated with hypertrophic cardiomyopathy (HCM), and significant reductions in gradient are noted after myectomy. Severe bleeding occasionally accompanies HCM, and abnormalities of von Willebrand factor (VWF) function are ubiquitous in obstructive HCM. In this investigation we compared the ability of HCM interventions to correct abnormalities of VWF. Twenty-six women, and 20 men, mean (SD) age 62 (14) years had 51 assessments of three independent measures of VWF function at the time of echocardiography. Fifteen patients reported either epistaxis or gastrointestinal bleeding. Patients were assessed before and after surgical septal myectomy (n=16), alcohol septal ablation (n=13) or discreet medical interventions (initiation or up-titration of beta blockers (n=12), disopyramide (n=6), pacing (n=2), amiodarone or verapamil, (n= 1 each)). Laboratory measures included platelet function analyzer 100 adenosine diphosphate closure time (PFA-100, normal < 121 seconds, non-closure 300 seconds), the ratio of VWF immunoturbidic activity to VWF antigen concentration (normal ≥ 0.8), and Western blot gel electrophoresis of VWF multimers (normal multimer distribution versus abnormal loss of highest molecular weight multimers). Thirty five patients had resting peak left ventricular outflow gradients > 30 mm Hg, and 11 had resting gradients ≤ 30 mm Hg but > 30 mm Hg with Valsalva maneuver. PFA-100 closure time correlated with peak instantaneous gradient, r=0.66. Highly significant reductions in all measures of VWF function were associated with septal myectomy (table), and all but one patient had correction of PFA-100 into the normal range (figure), and all myectomy patients had normal VWF multimers after surgery. Alcohol septal ablation showed less significant improvements in PFA-100 and VWF activity to antigen ratio, and it failed to normalize VWF multimers in 60 % of patients. Although medical therapy was associated with significant improvements in PFA-100 and gradient, it also did not correct the loss of high molecular weight multimers of VWF. Septal myectomy is more frequently associated with normalization of VWF function than is alcohol septal ablation or medical therapy. In patients with HCM and severe bleeding myectomy may be the preferred treatment.

Diurnal variation of von Willebrand factor in plasma: the Bispebjerg study of diurnal variations

Quantitation of von Willebrand factor (VWF) in plasma is a central element in assessing von Willebrand disease (VWD). VWF activity is known to vary, which has partly been ascribed to biological and preanalytical variation. However, a possible diurnal expression of VWF has not been thoroughly tested. We examined whether VWF antigen and VWF activity in plasma display a diurnal profile in healthy young males, and whether such variation is related to changes in release or elimination. Plasma from 20 healthy young males was collected at 9 time-points over 24 h (15 h of light and 9 h of darkness); the plasma concentration of melatonin was used as an internal control to confirm the normal 24-h rhythms of the individual participants. The data, analyzed by rhythmometric statistics, revealed a significant variation (P = 0.02) and total amplitude of 22.6% in VWF antigen concentrations over the 24-h period. A pronounced variation in VWF activity was also observed, although not significant according to the 24-h statistical model. To examine whether the diurnal pattern was related to changes in elimination or secretion, the ratio between (i) coagulation factor VIII and VWF and (ii) VWF propeptide and VWF was determined. Taken together, the data suggest changes in release and not in clearance. Diurnal variation in von Willebrand antigen and activity in plasma represents an important aspect of the biological variation. Standardized time-of-day plasma sampling for quantitation of VWF in VWD patients seems warranted.

Evaluation and performance characteristics of the Q Hemostasis Analyzer, an automated coagulation analyzer

The Q Hemostasis Analyzer (Grifols, Barcelona, Spain) is a fully-automated random-access multiparameter analyzer, designed to perform coagulation, chromogenic and immunologic assays. It is equipped with a cap-piercing system. The instrument was evaluated in a hemostasis laboratory of a University Hospital with respect to its technical features in the determination of coagulation i.e. prothrombin time (PT), activated partial thromboplastin time (aPTT), thrombin time, fibrinogen and single coagulation factors V (FV) and VIII (FVIII), chromogenic [antithrombin (AT) and protein C activity] and immunologic assays [von Willebrand factor antigen (vWF:Ag) concentration], using reagents from the analyzer manufacturer. Total precision (evaluated as the coefficient of variation) was below 6% for most parameters both in normal and in pathological ranges, except for FV, FVIII, AT and vWF:Ag both in the normal and pathological samples. No carryover was detected in alternating aPTT measurement in a pool of normal plasma samples and in the same pool spiked with unfractionated heparin (>1.5 IU/mL). The effective throughput was 154 PT, 66 PT/aPTT, 42 PT/aPTT/fibrinogen, and 38 PT/aPTT/AT per hour, leading to 154 to 114 tests performed per hour, depending of the tested panel. Test results obtained on the Q Hemostasis Analyzer were well correlated with those obtained on the ACL TOP analyzer (Instrumentation Laboratory), with r between 0.862 and 0.989. In conclusion, routine coagulation testing can be performed on the Q Hemostasis Analyzer with satisfactory precision and the same apply to more specialized and specific tests.

Hump-nosed pit viper (Hypnale hypnale) envenoming causes mild coagulopathy with incomplete clotting factor consumption

Context. Limited information exists on the coagulopathy caused by hump-nosed pit viper (Hypnale hypnale) envenoming. Objectives. This study aimed to characterise the coagulopathy in hump-nosed pit viper bites by measuring laboratory clotting times and factor studies. Materials and methods. Cases of hump-nosed pit viper envenoming were included from a prospective cohort study of Sri Lankan snake-bite patients. Patient age, sex, snake identification, time of bite and clinical effects were recorded. Patients did not receive anti-venom because no specific anti-venom to hump-nosed vipers exists. All patients received supportive care and serial 20-min whole blood clotting tests (WBCT20). The prothrombin time (PT), international normalised ratio (INR), activated partial thromboplastin time (aPTT), coagulation factors I, II, V, VII, VIII, IX and X, von Willebrand factor (vWF) antigen and D-Dimer concentrations were measured. The median of highest or lowest test result for each patient was reported with interquartile range (IQR). Results. There were 80 hump-nosed pit viper bites, median age was 37 years (IQR: 26–51 years) and 48 were male. The WBCT20 was positive in one patient. The median highest INR was 1.9 (1.5–2.2; Range: 1.3 to > 12) and median highest aPTT was 54 s (46–72 s; Range: 35–170 s). There was low fibrinogen [median: 1.3 g/L;1, –1.8 g/L; Range: < 0.2–2.9], low factor VIII levels [median: 23%; 16–37%] and low factor V levels [median: 43%; 23–74%]. D-Dimer concentrations [median: 3.4 mg/L; 2–7.4 mg/L] were slightly elevated. Factors II, VII and X and vWF antigen concentrations were normal. Discussion and Conclusions. Hump-nosed pit viper bites result in a mild coagulopathy which is usually not detected by a WBCT20. It is characterised by mild elevation of INR, low fibrinogen and Factors V and VIII which may be consistent with the venom containing a thrombin-like enzyme.

Acquired von Willebrand syndrome in multiple myeloma

Acquired von Willebrand syndrome (AvWS) is an uncommon complication of multiple myeloma (MM), and it is believed to be connected with paraprotein. The aim of this study was to determine the incidence of AvWS in patients with MM, and estimate the role of paraprotein in its occurrence. The study included 40 patients with MM. The plasma level of paraprotein, platelet adhesion on glass pearls, plasma von Willebrand factor antigen concentration, and ristocetin-induced platelet aggregation (RIPA) were measured initially. Absence of RIPA was found in six patients with MM (15%); however, all six of them had normal levels of von Willebrand factor antigen. Paraprotein was isolated from the serum of these patients. Platelet aggregation was measured in six healthy donors before and after addition of the isolated paraprotein. RIPA was significantly decreased in healthy donors in the presence of paraprotein (P<0·001). The same test was repeated with added human immunoglobulins for intravenous use without any change in RIPA. A significant negative correlation between plasma paraprotein level and RIPA was found (P<0·001). These investigations have shown that paraprotein is associated with AvWS in patients with MM.

Acquired type 2A von Willebrand syndrome caused by aortic valve disease corrects during valve surgery

Aortic valve (AV) defects can destroy high molecular weight multimers (HMWM) of von Willebrand factor (VWF), leading to acquired von Willebrand syndrome (aVWS) type IIA. This syndrome is considered a cause for increased perioperative bleeding in AV surgery. If diagnosed before operation, administration of VWF/FVIII concentrates is recommended. However, there is currently no evidence that the VWF HMWM defect persists during surgery long enough to require haemostatic therapy. We hypothesized that the preoperative VWF HMWM defect corrects already during cardiopulmonary bypass (CPB) before any haemostatic therapy. This prospective observational study enrolled 17 patients undergoing AV surgery, either isolated or associated with mitral valve or aorta surgery, and also 10 patients undergoing coronary artery bypass surgery (CABG) for comparison. VWF HMWM, VWF antigen (VWF:Ag) concentration, and collagen-binding capacity (VWF:CB) were measured before operation, directly after weaning from CPB, and on the first postoperative day. In 12 of the 17 subjects undergoing AV surgery (71%), VWF HMWM were abnormally absent before operation. At the end of CPB, VWF HMWM were normal in 15 of AV subjects (88%), and was normal in 16 subjects on the first postoperative day. VWF:Ag and VWF:CB were within or above the normal range at all three times. Two out of 10 subjects undergoing CABG (20%) had preoperative deficits of VWF HMWM that normalized after operation. Preoperative VWF HMWM defects corrected at the end of CPB in the absence of haemostatic therapy in most patients undergoing AV surgery. Diffuse bleeding occurring after CPB is unlikely to be related to persisting type 2A von Willebrand syndrome; other causes of coagulopathy should be suspected. Administration of VWF/FVIII concentrates appears unnecessary in this setting.

Factor deficiencies in venom-induced consumption coagulopathy resulting from Australian elapid envenomation: Australian Snakebite Project (ASP-10).

Limited information exists on the dynamics of hemostasis in patients with venom-induced consumption coagulopathy (VICC) from snake envenomation. The aim of the present study was to investigate specific factor deficiencies and their time course in Australasian elapid envenomation. We measured coagulation parameters and factor concentrations in patients recruited to the Australian Snakebite Project, an observational cohort study. There were 112 patients with complete VICC, defined as an international normalized ratio (INR) > 3, and 18 with partial VICC. Serial citrated plasma samples were collected from 0.5 to 60 h post-bite. INR, activated partial thromboplastin time (aPTT), coagulation factors (F)I, II, V, VII, VIII, IX, X, von Willebrand factor antigen (VWF:Ag) and D-dimer concentrations were measured. Complete VICC was characterized by near/total depletion of fibrinogen, FV and FVIII, with an INR and aPTT that exceeded the upper limits of detection, within 2 h of snakebite. Prothrombin levels never fell below 60% of normal, suggesting that the toxins were rapidly eliminated or inactivated and re-synthesis of clotting factors occurred irrespective of antivenom. Partial VICC caused limited depletion of fibrinogen and FV, and almost complete consumption of FVIII. Onset of VICC was more rapid with brown snake (Pseudonaja spp.) venom, which contains a group C prothrombin activator toxin, compared with the tiger snake group, which contains a group D prothrombin activator toxin and requires human FVa formation. Resolution of VICC occurred within 24-36 h irrespective of snake type. These results suggest that Australasian elapid prothrombin activators have a potent but short duration of action. Antivenom is unlikely to be administered in time to prevent VICC.

Von Willebrand Factor Antigen Concentration in Dogs with Sepsis

Von Willebrand factor (vWF) antigen concentration, a marker of endothelial activation, is increased in human patients with multiorgan failure, sepsis, or both, and is an independent predictor of survival. vWF antigen concentrations are significantly higher in dogs with sepsis. Fourteen dogs hospitalized with sepsis. Sepsis was defined as microbiologic or cytologic evidence of infection combined with systemic inflammatory response syndrome. Control dogs were healthy dogs, without evidence of disease. Prospective, observational study. Dogs admitted to the intensive care unit with a diagnosis of sepsis were considered eligible for enrollment into the study. Exclusion criteria included a previous diagnosis of von Willebrand disease or a recent history of a plasma transfusion. Citrated plasma samples were collected for analysis of vWF antigen by ELISA. All samples were drawn from dogs during hospitalization. Data between populations were analyzed using nonparametric statistical analysis with a P value < .05 considered significant. Twenty-five dogs were enrolled; 14 dogs with sepsis and 11 control dogs. The median vWF antigen concentration in dogs with sepsis was 156% (range, 117-200%), which was significantly higher than healthy dogs (105%; range, 44-155%, P < .005). There was no difference between survivors and nonsurvivors with a median vWF antigen concentration of 144% (range, 136-201%) in survivors (n = 7) and 159% (range, 122-174%) in nonsurvivors (n = 7) (P = .5). vWF is increased in dogs with sepsis, possibly reflecting endothelial activation. Further exploration of endothelial function is warranted in critically ill dogs.

Severe malaria is associated with a deficiency of von Willebrand factor cleaving protease, ADAMTS13

Severe falciparum malaria remains a major killer in tropical countries. Central in the pathophysiology is mechanical obstruction in the microcirculation caused by cytoadherence and sequestration of parasitized erythrocytes. However, the pathogenesis of many features complicating severe malaria, including coma, renal failure and thrombocytopenia, remains incompletely understood. These disease manifestations are also key features of thrombotic thrombocytopenic purpura, a life-threatening disease strongly associated with a deficiency of the von Willebrand factor (VWF) cleaving protease, ADAMTS13. We measured plasma ADAMTS13 activity, VWF antigen and VWF propeptide levels in 30 patients with severe falciparum malaria, 12 patients with uncomplicated falciparum malaria and 14 healthy Bangladeshi controls. In patients with severe malaria ADAMTS13 activity levels were markedly decreased in comparison to normal controls (mean [95%CI]: 23% [20-26] vs. 64% [55-72]) and VWF antigen and propeptide concentrations were significantly elevated (VWF antigen: 439% [396-481] vs. 64% [46-83]; VWF propeptide: 576% [481-671] vs. 69% [59-78]). In uncomplicated malaria VWF levels were also increased compared to healthy controls but ADAMTS13 activity was normal. The results suggest that decreased ADAMTS13 activity in combination with increased VWF concentrations may contribute to the complications in severe malaria.

ADAMTS13 and von Willebrand factor concentrations in patients with diabetes mellitus

The von Willebrand factor (VWF) is elevated in patients with diabetes mellitus and degraded by a metalloprotease, ADAMTS13. We hypothesized that this elevation is due to a decreased function of ADAMTS13. Thus, we investigated ADAMTS13 in patients with diabetes mellitus without and with peripheral artery occlusive disease (PAOD). When treating the latter group with dalteparin, VWF is reported to increase significantly, and we therefore measured ADAMTS13 also in these patients. VWF antigen and ADAMTS13 antigen and activity concentrations were measured in patients with diabetes mellitus but without PAOD (diabetes mellitus; n = 23) and with diabetes mellitus and PAOD (diabetes mellitus + PAOD; n = 65) before and after treatment with dalteparin or placebo. In the diabetes mellitus group, concentration of VWF antigen was significantly higher, whereas that of ADAMTS13 activity was significantly lower than in the healthy controls. In the diabetes mellitus along with PAOD group, VWF antigen was significantly higher, but ADAMTS13 antigen or activity did not differ significantly from those of healthy controls. The ADAMTS13 activity/antigen ratio was lower than in controls only in the diabetes mellitus patient group. VWF antigen increased significantly during dalteraprin treatment, whereas ADAMTS13 activity and antigen remained unchanged. Only patients with diabetes mellitus had significantly lower concentrations of ADAMTS13 activity in plasma than controls, although the diabetes mellitus along with PAOD had a more pronounced VWF antigen elevation than diabetes mellitus patients, illustrating a possible link between ADAMTS13 and microangiopathy in diabetes mellitus patients. The increase in VWF antigen concentration during treatment with dalteparin does not seem to be due to changes in ADAMTS13.