Perils, problems, and progress in laboratory diagnosis of von Willebrand disease

A comparative study in patients with type 2 von Willebrand disease using 4 different platelet-dependent von Willebrand factor assays

Background

Several assays are now available to evaluate platelet-dependent von Willebrand factor (VWF) activity.

Objective

To report the results obtained using 4 different assays in patients with von Willebrand disease (VWD) carrying variants mainly in the A1 domain, which is critical for VWF binding to glycoprotein Ib (GPIb) and ristocetin.

Methods

We evaluated 4 different assays, 2 gain-of-function mutant GPIb binding (VWF:GPIbM) and 2 ristocetin cofactor (VWF:RCo) assays, in 76 patients with type 2 VWD. Patients and healthy controls were tested using VWF:GPIbM enzyme-linked immunosorbent assay (ELISA), VWF:GPIbM automated, VWF:RCo aggregometric, and VWF:RCo automated assays.

Results

There was a good correlation (Pearson's r>0.82) and agreement (Bland-Altman plots assessment) between the 4 assays, although several outliers existed among the type 2B without high-molecular-weight multimers (HMWM). The VWF activity/VWF:antigen ratios, calculated for each assay, were used to establish the percentage of a correct diagnosis of type 2 (ratio<0.60) in these patients: VWF:RCo aggregometric, 2A(100%), 2M(78%), 2M/2A(100%), 2B(68%); VWF:RCo automated, 2A(88%), 2M(89%), 2M/2A(100%), 2B(63%); VWF:GPIbM ELISA, 2A(96%), 2M(67%), 2M/2A(67%), 2B(0%); VWF:GPIbM automated, 2A(73%), 2M(44%), 2M/2A(75%), 2B(84%). In type 2B patients with HMWM, all assays gave a ratio ≥0.60.

Conclusion

The VWF:GPIbM-automated assay is the most effective to diagnose as type 2 the 2B variants, whereas the VWF:RCo assays are the most effective in detecting 2M and 2M/2A variants. The VWF:GPIbM ELISA greatly overestimates the activity of the type 2B patients lacking HMWM. In this study, the use of a VWF activity/VWF:antigen ratio cut-off of 0.70 halved the number of misdiagnosed patients.

Reappraising the spectrum of bleeding gastrointestinal angioectasia in a degenerative calcific aortic valve stenosis: Heyde’s syndrome

Background

The occurrence of bleeding gastrointestinal angioectasia in elderly patients with degenerative calcific aortic stenosis is one of the most challenging clinical scenarios. A number of studies have shown that this clinical phenomenon is known as Heyde’s syndrome.

Main body of the abstract

The pathogenesis of Heyde’s syndrome is mainly due to the loss of high-molecular-weight von Willebrand factor (HMW vWF) multimers, as a consequent fragmentation of HMW vWF multimers as they pass through the stenosed aortic valve leading to acquired von Willebrand syndrome type IIA. Aortic valve replacement has proven to be a more effective management approach in the cessation of recurrent episodes of gastrointestinal bleeding.

Short conclusion

Physicians should have a high index of suspicion when dealing with elderly patients with established aortic stenosis presenting with iron deficiency anemia or unclear gastrointestinal bleeding. Parallel consultations between different specialties are essential for appropriate management.

Platelet Aggregation Assays Do Not Reliably Diagnose Platelet Delta Granule Storage Pool Deficiency

Background

Patients with platelet dysfunction disorders present with a variety of mucocutaneous bleeding symptoms including easy bruising, frequent epistaxis, bleeding gums upon tooth brushing and for women, heavy menstrual bleeding. Available laboratory assays to evaluate platelet function include the platelet function analyzer (PFA) and in larger centers with coagulation laboratories, light transmission platelet aggregometry (LTA) analyses. Both assays are known to have a number of limitations, especially in the diagnosis of platelet delta granule storage pool deficiency (δ-SPD). δ-SPD is an underdiagnosed condition caused by decreased numbers of platelet dense granules (DGs) and is best diagnosed by electron microscopy (EM). Patients with platelet δ-SPD have a decreased response to low levels of the agonist adenosine diphosphate (ADP) in the second wave of light transmittance with LTA or decreased ADP secretion by fluorescence lumiaggregometry. There are few reports that have evaluated patients with δ-SPD and their respective LTA results. One report published in 1987 described normal LTA assays in 23% of patients with δ-SPD; a more recent report described LTA as having the sensitivity to detect only about 52% of patients with δ-SPD. The purpose of our study was intended to review the LTA and EM results of patients suspected of having a platelet function disorder at our institution for comparison with previously published studies.

Methods

Our study included 344 patients who had been evaluated by both LTA and whole mount EM. Aggregometry utilized five agonists: ADP, epinephrine, collagen, arachidonic acid, and ristocetin. DGs were enumerated in 100 whole-mounted platelets to determine a mean number of dense granules per platelet (DGs/PL).

Results

Seventy-seven percent of our patients were found to have δ-SPD (264/344); 68% (179/264) of these subjects had an abnormal platelet LTA. Thirty-two percent (85/264) of our patients had normal LTA results but were found to have δ-SPD with a mean of 2.54 ± 0.15 DG/PL (normal = 4 - 6 DG/PL).

Conclusion

These data confirm previous reports suggesting the utilization of LTA alone in patients with histories of unexplained bleeding may miss the diagnosis of platelet δ-SPD. It is, therefore, prudent to assess platelet DG number by EM, especially if platelet LTA assessment is normal.

Increased von Willebrand factor parameters in children with febrile seizures

Introduction

Primary blood coagulation and wound sealing are orchestrated by von Willebrand factor (VWF), a large multimeric glycoprotein. Upon release of arginine vasopressin (AVP), VWF containing high molecular weight multimers is secreted. By measuring copeptin, the C-terminal part of the AVP prohormone, we recently found strongly increased AVP levels in children with febrile seizures (FS) as compared to children with fever but without seizures. It is unknown if increased AVP levels in FS are of any biological function. Therefore, our a priori hypothesis was that children with FS have increased VWF parameters in parallel with higher AVP levels.

Methods

We conducted a prospective, cross-sectional study of children aged between 6 months and 5 years. Children that presented at our emergency department with fever or a recent FS (within four hours) were evaluated to be included to the study. We measured serum copeptin and VWF parameters, including analyses of VWF:Antigen (WVF:Ag), VWF:collagen binding activity (VWF:CB) and VWF multimers in children with FS, febrile infections without seizures and additionally, in a non-febrile control group.

Results

We included 54 children in our study, 30 with FS, 10 in the febrile control group, and 14 in the non-febrile control group. Serum copeptin levels were significantly higher in children with FS (median [IQR] 24.73 pmol/l [13.65–68.65]) compared to the febrile control group (5.66 pmol/l [4.15–8.07], p = 0.002) and the non-febrile control group (4.78 pmol/l [3.33–5.3], p<0.001). VWF:CB levels were also significantly higher in children with FS (VWF:CB 2.29 U/ml [1.88–2.97]) as compared to the febrile (VWF:CB 1.41 U/ml [1.27–1.93], p = 0.048) and the non-febrile control group (VWF:CB 1.15 U/ml [0.98–1.21], p<0.001). VWF:Ag tended to be higher in children with FS compared to both control groups. Multivariate regression analysis revealed FS and copeptin as major determinants of VWF:CB.

Conclusions

Our results suggest that increased secretion of AVP in children with FS is associated with higher plasma levels of VWF parameters. Especially VWF:CB may serve as additional biomarker in the diagnosis of FS.

Assessment of the Stability of von Willebrand Profile Clotting Factors and Platelet Dense Granule Testing Following Air Transport

The purpose of this study was to determine the reliability of test results dependent upon blood and plasma sample stability when shipped by airfreight courier for reference laboratory assessment. Of particular interest was evaluation of von Willebrand profile assays and platelet dense granule storage pool analysis. Peripheral venous blood was obtained from healthy volunteers. von Willebrand factor (VWF) activity, VWF antigen, and factor VIII coagulant activity assays were performed immediately following venipuncture with additional aliquots of plasma frozen and stored at −70°C for subsequent analysis 48 hours later. One frozen aliquot was shipped via airfreight for analysis 48 hours later, with another frozen aliquot that remained on-site. Blood was also collected to enumerate platelet dense granules to determine whether shipment would affect results. Statistical analysis of all test results demonstrated significant correlation between immediately assayed samples and samples that were stored for 48 hours at −70°C (P < .0001), or frozen and shipped on dry ice (P < .0001) for analysis upon return to our laboratory. No difference was found in the mean number of platelet dense granules between samples retained in our laboratory or samples analyzed upon return of shipment (P = .751).

Role of multimeric analysis of von Willebrand factor (VWF) in von Willebrand disease (VWD) diagnosis: Lessons from the PCM-EVW-ES Spanish project

The multimeric analysis (MA) of plasma von Willebrand factor (VWF) evaluates structural integrity and helps in the diagnosis of von Willebrand disease (VWD). This assay is a matter of controversy, being considered by some investigators cumbersome and only slightly informative. The centralised study ‘Molecular and Clinical Profile of von Willebrand Disease in Spain (PCM-EVW-ES)’ has been carried out by including the phenotypic assessment and the genetic analysis by next generation sequencing (NGS) of the VWF gene (VWF). The aim of the present study was to evaluate the role of MA to the diagnosis of these patients and their potential discrepancies. Two hundred and seventy out of 480 patients centrally diagnosed with VWD had normal multimers, 168 had abnormal multimers and 42 a total absence of multimers. VWF MA was of great significance in the diagnosis of 83 patients (17.3%), it was also of help in the diagnosis achieved in 365 additional patients (76%) and was not informative in 32 cases (6.7%). With regard to discrepancies, 110 out of 480 (23%) patients centrally diagnosed with VWD presented some kind of discordance between VWF:RCo/VWF:Ag and/or VWF:CB/VWF:Ag ratios, multimeric study and/or genetic results. The VWF MA was key in the presence of novel mutations as well as in cases with phenotypic discrepancies. A comparison between the contribution of MA and VWF:CB showed a clearly higher contribution of the former in the diagnostic process. These data seem to reinforce the relevance of the VWF MA in VWD diagnosis, despite all its limitations.

Preclinical evaluation of a semi-automated and rapid commercial electrophoresis assay for von Willebrand factor multimers

BACKGROUND

The von Willebrand factor (VWF) multimer test is required to correctly subtype qualitative type 2 von Willebrand disease (VWD). The current VWF multimer assays are difficult, nonstandardized, and time-consuming. The purpose of this study was to evaluate the clinical utility of the commercial VWF multimer kit by Sebia (Lisses, France), an electrophoresis technique yielding same-day results.

METHODS

Ten healthy volunteer plasma samples, in-house reference plasma (IRP) and commercial normal plasma (CNP) samples, 10 plasma samples from patients with a known VWD type, 1 hemophilia A plasma sample, and 7 external quality assurance (EQA) samples were analyzed using the commercial VWF multimer kit. Additional coagulation testing included measurements of VWF antigen (VWF:Ag), VWF activity (VWF:Ac), and FVIII activity (FVIII:C).

RESULTS

The CNP results revealed a relative loss of the highest molecular weight multimers; therefore, IRP was preferred as the reference sample. The interpretations of 10 patients with a known VWD type could be successfully reproduced and agreed with previous VWF multimer results. In all EQA surveys, the multimer results and final VWD diagnosis agreed with expert opinion.

CONCLUSIONS

The VWF multimer assay by Sebia is easy to perform and can be successfully implemented in any clinical laboratory for second-stage evaluation of VWD. The resolution power of multimer distribution is adequate to correctly classify VWD types 1, 2A, 2B, and 3.

Towards personalised therapy for von Willebrand disease: a future role for recombinant products

von Willebrand disease (VWD) is reportedly the most common bleeding disorder and is caused by deficiencies and/or defects in the adhesive plasma protein von Willebrand factor (VWF). Functionally, normal VWF prevents bleeding by promoting both primary and secondary haemostasis. In respect to primary haemostasis, VWF binds to both platelets and sub-endothelial matrix components, especially collagen, to anchor platelets to damaged vascular tissue and promote thrombus formation. VWF also stabilises and protects factor VIII in the circulation, delivering FVIII to the site of injury, which then facilitates secondary haemostasis and fibrin formation/thrombus stabilisation. As a result of this, patients with VWD suffer a bleeding diathesis reflective of a primary defect caused by defective/deficient VWF, which in some patients is compounded by a reduction in FVIII. Management of VWD, therefore, chiefly entails replacement of VWF, and sometimes also FVIII, to protect against bleeding. The current report principally focuses on the future potential for "personalised" management of VWD, given the emerging options in recombinant therapies. Recombinant VWF has been developed and is undergoing clinical trials, and this promising therapy may soon change the way in which VWD is managed. In particular, we can envisage a personalised treatment approach using recombinant VWF, with or without recombinant FVIII, depending on the type of VWD, the extent of deficiencies, and the period and duration of treatment.

Rapid discrimination of the phenotypic variants of von Willebrand disease

Approximately 20% to 25% of patients with von Willebrand disease (VWD) have a qualitative defect of the von Willebrand factor (VWF) protein activities. Variant VWD typically is classified as type 1C, 2A, 2B, 2M, or 2N depending on the VWF activity defect. Traditionally, diagnosis has relied on multiple clinical laboratory assays to assign VWD phenotype. We developed an enzyme-linked immunosorbent assay (ELISA) to measure the various activities of VWF on a single plate and evaluated 160 patient samples enrolled in the Zimmerman Program for the Molecular and Clinical Biology of von Willebrand Disease with type 2 VWD. Using linear discriminate analysis (LDA), this assay was able to identify type 1C, 2A, 2B, 2M, or 2N VWD with an overall accuracy of 92.5% in the patient study cohort. LDA jackknife analysis, a statistical resampling technique, identified variant VWD with an overall accuracy of 88.1%, which predicts the assay's performance in the general population. In addition, this assay demonstrated correlation with traditional clinical laboratory VWF assays. The VWF multiplex activity assay may be useful as a same-day screening assay when considering the diagnosis of variant VWD in an individual patient.

Von Willebrand factor in patients on mechanical circulatory support - a double-edged sword between bleeding and thrombosis

Mechanical circulatory support (MCS) is an umbrella term describing the various technologies used in both short- and long-term management of patients with either end-stage chronic heart failure (HF) or acute HF. Most often, MCS has emerged as a bridge to transplantation, but more recently it is also used as a destination therapy. Mechanical circulatory support includes left ventricular assist device (LVAD) or bi-ventricular assist device (Bi-VAD). Currently, 2- to 3-year survival in carefully selected patients is much better than with medical therapy. However, MCS therapy is hampered by sometimes life-threatening complications including bleeding and device thrombosis. Von Willebrand factor (vWF) has two major functions in haemostasis. First, it plays a crucial role in platelet-subendothelium adhesion and platelet-platelet interactions (aggregation). Second, it is the carrier of factor VIII (FVIII) in plasma. Von Willebrand factor prolongs FVIII half-time by protecting it from proteolytic degradation. It delivers FVIII to the site of vascular injury thus enhancing haemostatic process. On one hand, high plasma levels of vWF have been associated with an increased risk of thrombosis. On the other, defects or deficiencies of vWF underlie the inherited von Willebrand disease or acquired von Willebrand syndrome. Here we review the pathophysiology of thrombosis and bleeding associated with vWF.