Laboratory tests used to help diagnose von Willebrand disease: an update

Application of a strain rate gradient microfluidic device to von Willebrand's disease screening

Von Willebrand's disease (VWD) is the most common inherited bleeding disorder caused by either quantitative or qualitative defects of von Willebrand factor (VWF). Current tests for VWD require relatively large blood volumes, have low throughput, are time-consuming, and do not incorporate the physiologically relevant effects of haemodynamic forces. We developed a microfluidic device incorporating micro-contractions that harnesses well-defined haemodynamic strain gradients to initiate platelet aggregation in citrated whole blood. The microchannel architecture has been specifically designed to allow for continuous real-time imaging of platelet aggregation dynamics. Subjects aged ≥18 years with previously diagnosed VWD or who presented for evaluation of a bleeding disorder, where the possible diagnosis included VWD, were tested. Samples were obtained for device characterization as well as for pathology-based testing. Platelet aggregation in the microfluidic device is independent of platelet amplification loops but dependent on low-level platelet activation, GPIb/IX/V and integrin α_IIbβ₃ engagement. Microfluidic output directly correlates with VWF antigen levels and is able to sensitively detect aggregation defects associated with VWD subtypes. Testing demonstrated a strong correlation with standard clinical laboratory-based tests. Head-to-head comparison with PFA100® demonstrated equivalent, if not improved, sensitivity for screening aggregation defects associated with VWD. This strain rate gradient microfluidic prototype has the potential to be a clinically useful, rapid and high throughput-screening tool for VWD as well as other strain-dependent platelet disorders. In addition, the microfluidic device represents a novel approach to examine the effects of high magnitude/short duration (ms) strain rate gradients on platelet function.

Clinical utility of closure times using the platelet function analyzer-100/200

The "platelet function analyzer" (PFA)-100 was first introduced to us in 1995. Since then, the instrument has appeared in over 50 reviews and almost 1000 publications. Recently, the PFA-100 has been "upgraded" to the PFA-200, which has transformed the user interface and electronic management, but retained the fundamental mechanics, and essentially provides the same results. The PFA-100/200 has conceivable clinical utility to screen for von Willebrand Disease (VWD) and platelet disorders, and in monitoring desmopressin (DDAVP) therapy in both, and possibly anti-platelet therapy. Its great strengths are its usage simplicity and sensitivity to conditions affecting primary hemostasis. However, as a "global" test, its limitation is that closure time (CT) test results are neither predictive of, nor specific for, any individual disorder. However, utilized properly, the PFA-100/200 reflects a valuable addition to hemostasis laboratories involved in identification or therapeutic-monitoring of disorders of primary hemostasis.

Laboratory Testing for von Willebrand Factor Ristocetin Cofactor (VWF:RCo)

von Willebrand disease (VWD) is reportedly the most common inherited bleeding disorder and can also arise as an acquired syndrome (AVWS). These disorders develop due to defects and/or deficiency of the plasma protein von Willebrand factor (VWF). Laboratory testing for these VWF-related disorders requires assessment of both VWF level and VWF activity, the latter requiring multiple assays because of the many functions carried out by VWF to help prevent bleeding. The current paper describes several protocols for assessment of VWF activity by means of VWF ristocetin cofactor (VWF:RCo). These assays identify VWF activity by quantitative assessment of VWF protein adhesion to platelets or other particles and subsequent detection of the adhered VWF as facilitated by inclusion of ristocetin. The most commonly performed assays for VWF:RCo comprise platelet agglutination assays, latex agglutination assays, and chemiluminescent assay (CLIA), with three of these described in this chapter.

Diagnosis or Exclusion of von Willebrand Disease Using Laboratory Testing

von Willebrand disease (VWD) is a common bleeding disorder diagnosed based on clinical features and following laboratory testing. VWD is due to deficiencies or defects in the plasma protein von Willebrand factor (VWF), a large adhesive protein with multiple activities. Laboratory testing therefore centers on assessment of VWF protein level using VWF antigen (VWF:Ag), as well as assays that measure VWF activity, most notably platelet glycoprotein (GP) Ib and collagen binding (VWF:CB) activities. Decreases in VWF:Ag and VWF activities, as well as the pattern of such changes, help define VWD and its type. Classically, the most often used assay for measuring GPIb binding activity was the ristocetin cofactor assay (VWF:RCo), which historically measured agglutination of fixed human platelets by VWF in the presence of ristocetin. This assay is now often replaced or supplemented with other assays based on binding of VWF to recombinant GPIb, generally without the use of platelets, and with or without ristocetin. This chapter briefly reviews laboratory tests for VWD, as well as recommended approaches to use of such assays to help diagnose or exclude VWD in patients showing clinical features.

Laboratory Testing for von Willebrand Factor: Factor VIII Binding (for 2N VWD)

Von Willebrand disease (VWD) is reportedly the most common inherited bleeding disorder and can also arise as an acquired syndrome (AVWS). These disorders develop due to defects and/or deficiency of the plasma protein von Willebrand factor (VWF). Laboratory testing for the VWF-related disorders requires assessment of both VWF level and VWF activity, the latter requiring multiple assays because of the many functions carried out by VWF to help prevent bleeding. The current paper describes a protocol for assessment of VWF activity by means of VWF: factor VIII binding (VWF:FVIIIB). Such assays identify VWF activity by quantitative assessment of VWF protein adhesion to FVIII, which is the activity lost in type 2N VWD. This assay is therefore a critical assay for identification or exclusion of 2N VWD. The most commonly performed assays for VWF:FVIIIB comprise enzyme-linked immunosorbent assays (ELISA), and such an assay is described in this chapter.

Laboratory Testing for von Willebrand Factor Antigen (VWF:Ag)

von Willebrand disease (VWD) is reportedly the most common inherited bleeding disorder and can also arise as an acquired syndrome (AVWS). These disorders arise due to defects and/or deficiency of the plasma protein von Willebrand factor (VWF). Laboratory testing for the VWF-related disorders requires assessment of both VWF level and VWF activity, the latter requiring multiple assays because of the many functions carried out by VWF to help prevent bleeding. The current paper describes protocols for assessment of VWF level by means of VWF antigen (VWF:Ag). These assays identify VWF levels by quantitative assessment of VWF protein by means of immunological assays. The most commonly performed assays for VWF:Ag comprise enzyme-linked immunosorbent assays (ELISA) and latex-enhanced immunoassays (LIA), as described in this chapter.

Utility of the von Willebrand factor collagen binding assay in the diagnosis of von Willebrand disease

von Willebrand Disease (VWD) is the most common inherited bleeding disorder and also arises as an acquired defect (AVWS). VWD and AVWS are due to quantitative deficiencies and/or qualitative defects in von Willebrand factor (VWF), an adhesive plasma protein with multiple activities. Diagnosis of VWD is problematic, being subject to overdiagnosis, underdiagnosis, and misdiagnosis. This is largely due to limitations in current test procedures and an over-reliance on these imperfect test systems for clinical diagnosis. VWF essentially acts to assist in the formation of a platelet thrombus to stop blood loss from sites of injury, achieving this by binding to platelets (primarily through the glycoprotein Ib receptor), binding to subendothelial matrix components (primarily collagen), and binding to factor VIII (FVIII), thus protecting FVIII from degradation and enabling its delivery to sites of vascular injury. VWD is classified into six separate types, which may each be differentially managed therapeutically, and this underscores the importance of a correct diagnosis. The current report concisely reviews the utility of a relatively underutilised assay, the VWF collagen binding assay (VWF:CB), in facilitating the correct diagnosis and typing of VWD. In particular, if laboratories do not utilise the VWF:CB, then (i) type 2M VWD will continue to be missed, and/or misdiagnosed as types 2A or 1 VWD, and (ii) types 2A, 2B and PT-VWD will continue to be missed, or else be misdiagnosed as type 1 VWD or ITP. Am. J. Hematol. 92:114-118, 2017. © 2016 Wiley Periodicals, Inc.

Laboratory Testing for von Willebrand Factor Activity by Glycoprotein Ib Binding Assays (VWF:GPIb)

In addition to assessment of von Willebrand factor (VWF) antigen (VWF:Ag), the first-line laboratory investigation of possible von Willebrand disease (VWD) often includes an assay to measure GPIb (glycoprotein Ib) binding activity of VWF. A decreased GPIb binding activity is characteristic for most of the VWD types. For many years, the most frequently used assay for measuring GPIb binding activity was the ristocetin cofactor assay (VWF:RCo), which measures the agglutination of fixed human platelets by VWF in the presence of ristocetin. Because of performance issues, including high assay variability and a lack of VWF sensitivity, this assay is currently being replaced or supplemented by assays based on the binding of VWF to recombinant GPIb. One published method (now abbreviated VWF:GPIbR) uses wild-type GPIb for triggering the binding reaction in the presence of ristocetin. Another more widely used method (now abbreviated VWF:GPIbM) uses gain-of-function GPIb without ristocetin; this permits spontaneous binding of VWF to GPIb and avoids problems associated with the nonphysiological substance ristocetin. The binding of VWF to GPIb can be quantified by using different principles, e.g., ELISA, particle agglutination, or chemiluminescence. The following chapter describes a ristocetin-free method based on particle agglutination in more detail.

Laboratory Testing for von Willebrand Factor Collagen Binding (VWF:CB)

Von Willebrand disease (VWD) is reportedly the most common inherited bleeding disorder and can also arise as an acquired syndrome (AVWS). These disorders develop due to defects and/or deficiency of the plasma protein von Willebrand factor (VWF). Laboratory testing for the VWF-related disorders requires assessment of both VWF level and VWF activity, the latter requiring multiple assays because of the many functions carried out by VWF to help prevent bleeding. This chapter describes several protocols for assessment of VWF activity by means of VWF collagen binding (VWF:CB). These assays identify VWF activity by quantitative assessment of VWF protein adhesion to collagen or collagen peptides and subsequent immunological detection of the adhered VWF. The most commonly performed assays for VWF:CB comprise enzyme-linked immunosorbent assays (ELISA) and chemiluminescent assay (CLIA), as described in this chapter.

Laboratory Testing for Von Willebrand Factor Multimers

Von Willebrand disease (VWD) is reportedly the most common inherited bleeding disorder and can also arise as an acquired syndrome (AVWS). These disorders develop due to defects and/or deficiency of the plasma protein von Willebrand factor (VWF). Laboratory testing for the VWF-related disorders requires assessment of both VWF level and VWF activity, the latter requiring multiple assays because of the many functions carried out by VWF to help prevent bleeding. As an additional step, an evaluation of VWF structural features by multimer analysis is useful in selective investigations. The current paper therefore describes a protocol for assessment of VWF multimers by gel electrophoresis, thus enabling identification of protein bands that represent differently sized multimers. The sample protocol described in this chapter is the methodology developed by Sebia.

Overview of Hemostasis and Thrombosis and Contribution of Laboratory Testing to Diagnosis and Management of Hemostasis and Thrombosis Disorders

Hemostasis is a complex and tightly regulated process whereby the body attempts to maintain a homeostatic balance to permit normal blood flow, without bleeding or thrombosis. When this balance is disrupted, due to trauma or underlying congenital bleeding or thrombotic disorders, clinical intervention may be required. To assist clinicians in diagnosing and managing affected patients, hemostasis laboratories offer an arsenal of tests, both routine (screening) and more specialized (diagnostic). In general, screening assays are used to screen for hemostasis-related disease or to monitor or measure the effect of anticoagulant therapy, which may be applied to treat patients with recent thrombosis or at risk of thrombosis. Diagnostic assays are used to diagnose or exclude specific hemostasis-related diseases, and in some cases, to monitor or measure the effect of anticoagulant therapy, or alternatively procoagulant therapy that may be applied to those at risk of bleeding. This chapter provides an overview of hemostasis and thrombosis with respect to laboratory tests that may be applied to affected patients.