Laboratory assessment as a critical component of the appropriate diagnosis and sub-classification of von Willebrand's disease

The Role of the von Willebrand Factor Collagen-Binding Assay (VWF:CB) in the Diagnosis and Treatment of von Willebrand Disease (VWD) and Way Beyond: A Comprehensive 36-Year History

The von Willebrand factor (VWF) collagen binding (VWF:CB) assay was first reported for use in von Willebrand diagnostics in 1986, by Brown and Bosak. Since then, the VWF:CB has continued to be used to help diagnose von Willebrand disease (VWD) (correctly) and also to help assign the correct subtype, as well as to assist in the monitoring of VWD therapy, especially desmopressin (DDAVP). However, it is important to recognize that the specific value of any VWF:CB is predicated on the use of an optimized VWF:CB, and that not all VWF:CB assays are so optimized. There are some good commercial assays available, but there are also some "not-so-good" commercial assays available, and these may continue to give the VWF:CB "a bad reputation." In addition to VWD diagnosis and management, the VWF:CB found purpose in a variety of other applications, from assessing ADAMTS13 activity, to investigation into acquired von Willebrand syndrome (especially as associated with use of mechanical circulatory support or cardiac assist devices), to assessment of VWF activity in disease states in where an excess of high-molecular-weight VWF may accumulate, and lead to increased (micro)thrombosis risk (e.g., coronavirus disease 2019, thrombotic thrombocytopenic purpura). The VWF:CB turns 37 in 2023. This review is a celebration of the utility of the VWF:CB over this nearly 40-year history.

Extracorporeal membrane oxygenation improves coagulopathy in an experimental traumatic hemorrhagic model

Purpose

Hemorrhage is the most common cause of preventable death after trauma. Coagulopathy plays a central role in uncontrolled bleeding and is caused by multiple factors. Extracorporeal Membrane Oxygenation (ECMO) is an established treatment for patients with respiratory failure and has in recent years also been used in severely injured trauma patients with cardiopulmonary failure and coexisting bleeding shock. The aim of this study was to evaluate the effect of ECMO on hypothermia, acidosis, and coagulopathy in a traumatic hemorrhagic rabbit model.

Methods

After anesthesia and tracheostomy, ten New Zealand White rabbits sustained laparotomy, bilateral femur fractures and were hemorrhaged 45% of their estimated blood volume. After 90 min of hemorrhagic shock they were resuscitated with a standard transfusion protocol together with venoarterial ECMO (n = 5) or with a standard transfusion protocol only (n = 5) for 60 min. No systemic heparin was administered.

Results

ECMO during 60 min of resuscitation significantly increased heart rate (p = 0.01), mean arterial pressure (p = 0.01), body temperature (p = 0.01) and improved the metabolic acidosis, pH (p = 0.01), and lactate (p = 0.01). ECMO also improved the coagulation capacity measured in vitro by Rotational Thromboelastometry with a significant decrease in clot formation time (p < 0.01). This finding was confirmed in vivo with a significant reduction in the animals’ ear bleeding time (p < 0.01) and cuticle bleeding time (p < 0.01); 5/5 animals survived in the ECMO group and 3/5 animals survived in the control group.

Conclusions

Heparin-free ECMO stabilizes circulation, improves coagulation, and may impact short-time survival, during the first 60 min, in an experimental traumatic model with severe hemorrhagic shock.

Determination of von Willebrand Factor Activity: Evaluation of the HaemosIL™ Assay in Comparison With Established Procedures

Determination of von Willebrand factor activity is required for diagnosis and classification of von Willebrand disease. In addition, von Willebrand factor activity can be of prognostic relevance in several clinical entities including thromboembolic and cardiovascular disorders in which elevated activity correlates with a poor prognosis. The HaemosIL™ assay (Instrumentation Laboratory GmbH, Munich, Germany) provides a new fully automated procedure for determination of von Willebrand factor activity. This assay measures binding of the von Willebrand factor to GP Ibα of the platelet glycoprotein complex Ib-V-IX. In our study, we analyzed 300 samples including those of patients with hereditary von Willebrand disease. The results obtained with the HaemosIL™ assay were compared to von Willebrand factor activities determined by established procedures. Activities determined with HaemosIL™ correlated with those activities determined as ristocetin cofactor (r = 0.88, p < 0.0001), collagen-binding (r = 0.93, p < 0.0001), and GP Ib-binding (r = 0.91, p < 0.0001). The comparability of results obtained by HaemosIL™ and the GP Ib-binding ELISA were excellent ([HaemosIL™] = 0.96 ∞ activity [GP Ib-binding ELISA] + 10.7), whereas activities determined by ristocetin cofactor or collagen-binding revealed more variance. Like the other assays, the HaemosIL™ failed to indicate a loss of high-molecular-weight von Willebrand factor multimers. The HaemosIL™ assay can replace the GP Ib-binding ELISA for the determination of von Willebrand factor activity. Advantages of this assay include accuracy of results, full automation, and, thus, broad availability. Since the assay does not predict the absence of high-molecular-weight multimers, multimeric analysis remains the procedure of choice for the differentiation of functional defects.

Evaluation of an heterogeneous group of patients with von Willebrand disease using an assay alternative to ristocetin induced platelet agglutination

BACKGROUND

Diagnosis of von Willebrand disease (VWD) type 2 usually relies on the discrepancy between the von Willebrand factor (VWF) ristocetin cofactor activity (VWF:RCo) and VWF antigen (VWF:Ag). Type 2B patients can be discriminated from other qualitative VWD variants by using ristocetin-induced platelet agglutination (RIPA) test. The major limitation of RIPA is the requirement of fresh blood sample.

OBJECTIVES

In this study, we evaluated the VWF gain-of-function mutant GPIb binding (VWF:GPIbM) and VWF:RCo assays to investigate whether the VWF:GPIbM/VWF:RCo ratio was able to identify the type 2B variant among an heterogeneous VWD population, previously characterized following the ISTH-SSC guidelines.

PATIENTS/METHODS

Seventy-six VWD patients and 31 healthy subjects were evaluated by using VWF:Ag, VWF:RCo, and VWF:GPIbM assays.

RESULTS

The mean (minimum-maximum values) VWF:GPIbM/VWF:RCo ratio was higher in type 2B patients (2.53, 0.84-6.11) than in healthy controls (1.05, 0.87-1.34), type 1 (0.85, 0.51-1.15), 2A (1.20, 0.36-2.82), and 2M (1.07, 0.91-1.38) (P < 0.0001). Type 2B variants were divided into four groups (A, B, C, and D) according to their different multimeric patterns. The mean value of the VWF:GPIbM/VWF:RCo ratio in the four groups showed an increasing trend from group A (1.08) to D (3.69), proportional to the loss of high molecular weight multimers. Among 32 type 2B patients, previously diagnosed with RIPA, 8 (mainly with a type I New York/Malmö phenotype) were not confirmed using the VWF:GPIbM/VWF:RCo ratio.

CONCLUSIONS

Whenever the RIPA test is not feasible, the VWF:GPIbM/VWF:RCo ratio might help to identify severe type 2B VWD patients.

A two-centre comparative evaluation of new automated assays for von Willebrand factor ristocetin cofactor activity and antigen

von Willebrand disease (VWD) is caused by a quantitative and/or qualitative deficiency of the von Willebrand factor (VWF). The laboratory diagnosis of VWD is dependent on the measurement of VWF antigen (VWF:Ag) and ristocetin cofactor activity (VWF:RCo). The aim of this study was to undertake a two-centre evaluation of two new automated VWF:Ag and VWF:RCo assays systems from Instrumentation Laboratory (Bedford, USA). Using the two new analytical systems that operated with different detection principles: immunoturbidimetric (TOP500 analyser) and chemiluminescent (AcuStar analyser), VWF:Ag and VWF:RCo levels were determined in samples from 171 healthy normal subjects, 80 VWD patients (16 type 1, 58 type 2 and 6 type 3) and 7 acquired von Willebrand syndrome patients. With commercial lyophilized normal and pathological plasmas VWF: Ag and VWF:RCo assays performed on both analysers exhibited low levels of inter-assay imprecision (AcuStar: CV% range 3.3-6.9; TOP500: CV% range 2.6-6.3). Samples from normal healthy subjects (range: VWF:Ag 44.6-173.9 IU dL(-1) ; VWF:RCo 43.1-191.5 IU dL(-1)) and patients (range: VWF:Ag <0.3-115.1 IU dL(-1) ; VWF:RCo <0.5-57.2 IU dL(-1)) showed a good correlation between the two VWF:Ag and VWF:RCo methods (rs = 0.92 and 0.82 respectively), with only a few inconsistent cases among the patients' samples evaluated. The chemiluminescent assays had a lower limit of detection for both VWF:Ag and VWF:RCo compared to immunoturbidimetric tests (0.3 IU dL(-1) vs. 2.2 IU dL(-1) and 0.5 IU dL(-1) vs. 4.4 IU dL(-1) respectively). The TOP500 and AcuStar VWF:Ag and VWF:RCo assays were precise and compare well between centres, making these systems suitable for the diagnosis of VWD in non-specialized and reference laboratories.

The platelet-function analyzer (PFA-100 ® ) for evaluating primary hemostasis

The platelet-function analyzer, PFA-100, is a relatively novel method for rapid in vitro global evaluation of primary hemostasis. The aim of this review is to summarize the published studies reporting on the utility of the PFA-100 device as a screening tool for primary hemostasis. Data were identified by searches of the published literature, including PubMed, references from reviews and abstracts from the most important meetings on this topic. The literature data support the use of the PFA-100 as a useful screening tool for the investigation of von Willebrand's disease and other acquired and congenital intrinsic platelet function disorders. Moreover, it is useful for evaluating primary hemostasis before surgical procedures and for monitoring desmopressin therapy in both von Willebrand's disease and platelet function disorders. Given its high sensitivity, speed and simplicity of use, we conclude that the PFA-100 could replace the in vivo bleeding time as a screening test for primary hemostasis in routine clinical practice.

A comparative evaluation of a new automated assay for von Willebrand factor activity

The ristocetin cofactor assay (VWF:RCo) is the reference method for assessing von Willebrand factor (VWF) activity in the diagnosis of von Willebrand's Disease (VWD). However, the assay suffers from poor reproducibility and sensitivity at low levels of VWF and is labour intensive. We have undertaken an evaluation of a new immunoturbidimetric VWF activity (VWF:Ac) assay (INNOVANCE(®) VWF Ac. Siemens Healthcare Diagnostics, Marburg, Germany) relative to an established platelet-based VWF:RCo method. Samples from 50 healthy normal subjects, 80 patients with VWD and 50 samples that exhibited 'HIL' (i.e. Haemolysis, Icterus or Lipaemia) were studied. VWF:Ac, VWF:RCo and VWF:Ag were performed on a CS-analyser (Sysmex UK Ltd, Milton Keynes, UK), all reagents were from Siemens Healthcare Diagnostics. The VWF:Ac assay, gave low intra- and inter-assay imprecision (over a 31-day period, n = 200 replicate readings) using commercial normal (Mean 96.2 IU dL(-1), CV < 3.0%) and pathological (Mean 36.1 IU dL(-1), CV < 3.5%) control plasmas. The normal and clinical samples exhibited good correlation between VWF:RCo (range 3-753 IU dL(-1)) and VWF:Ac (rs = 0.97, P < 0.0001), with a mean bias of 5.6 IU dL(-1). Ratios of VWF:Ac and VWF:RCo to VWF:Ag in the VWD samples were comparable, although VWF:Ac had a superior lower level of detection to that of VWF:RCo (3% and 5% respectively). A subset (n = 97) of VWD and HIL samples were analysed for VWF:Ac at two different dilutions to assess the effect on relative potency, no significant difference was observed (P = 0.111). The INNOVANCE(®) VWF Ac assay was shown to be reliable and precise.

Establishment and characterization of a new and stable collagen-binding assay for the assessment of von Willebrand factor activity

Introduction

Laboratory diagnosis of von Willebrand disease (VWD) requires determination of both von Willebrand factor (VWF) protein levels and activity. Current VWF activity tests include the ristocetin cofactor assay and the collagen-binding assay (VWF:CB). The goal of this investigation is to characterize a new collagen-binding assay and to determine its effectiveness in identifying VWD.

Methods

Analytical studies were carried out to characterize the performance of a new VWF:CB ELISA. Additionally, samples from a normal population were tested as were well-characterized type 1 and type 2 VWD samples.

Results

Repeatability and within-laboratory precision studies resulted in coefficients of variation (CVs) of ≤11%. A linear range of 1–354% (0.01–3.54 IU/mL) was determined, along with a limit of detection and a lower limit of quantitation of 1.6% and 4.0% (0.016 and 0.04 IU/mL), respectively. Samples tested from apparently healthy individuals resulted in a normal range of 54–217% (0.54–2.17 IU/mL). Known VWD type 1 and type 2 samples were also analyzed by the ELISA, with 99% of samples having VWF:CB below the normal reference range and an estimated 96% sensitivity and 87% specificity using a VWF collagen-binding/antigen cutoff ratio of 0.50.

Conclusion

This new VWF:CB ELISA provides an accurate measure of collagen-binding activity that aids in the diagnosis and differentiation of type 1 from type 2 VWD.

Evaluation of an automated platelet-based assay of ristocetin cofactor activity

von Willebrand's disease (VWD) is regarded as the most common congenital bleeding disorder, and although not available in all laboratories von Willebrand factor (VWF) activity is most frequently assessed as ristocetin cofactor (VWF:RCo). This test can be technically challenging, is subject to poor sensitivity (∼20 IU dL(-1) VWF:RCo) and has a high degree of inter- and intra-assay imprecision [coefficient of variation (cv) > 25%]. We studied an automated assay using a combined fixed platelet/ristocetin reagent (BC von Willebrand reagent, Siemens Healthcare Diagnostics) on the CS-2000i analyser (Sysmex UK Ltd). Initially inter- and intra-assay imprecision was assessed. The automated method showed good day-to-day reproducibility and linearity of standard curves. This technique, also gave low intra- and inter-assay imprecision using commercial normal (cv < 4.5%) and pathological (cv < 8.1%) control plasmas. We then compared automated technique results from 30 healthy normal subjects and 39 VWD patients to those obtained using standard aggregometry (Bio/Data, PAP4) with lyophilised fixed platelets (Helena BioSciences) and ristocetin (American Biochemical and Pharmaceutical Ltd). The automated method had a sensitivity limit of approximately 10 IU dL(-1) vs. 20 IU dL(-1) for aggregometry. Samples giving results within the aggregometry measurable range (n = 50) exhibited good correlation with the automated technique (median 70 IU dL(-1), range 7-184 IU dL(-1); and 64 IU dL(-1), 6-138 IU dL(-1) respectively; R(2) = 0.85). We subsequently compared 3 different batches of BC von Willebrand reagent, using a second group of normal subjects and VWD patients (n = 35, 55-139 IU dL(-1) and n = 30, <10-50 IU dL(-1)). The CS-2000i results exhibited no clinically significant variation between batches (mean cv = 7%). The automated VWF:RCo assay offers a more sensitive, reproducible, robust and less laborious alternative to standard aggregometry.

Correlation between von Willebrand factor antigen, von Willebrand factor ristocetin cofactor activity and factor VIII activity in plasma

BACKGROUND

The laboratory diagnosis of von Willebrand Factor (VWF) deficiencies includes qualitative and quantitative measurements of VWF and clotting factor VIII (FVIII). Since the FVIII activity is frequently normal in patients with mild type 1 or 2 von Willebrand disease (VWD), there is controversy whether FVIII testing should accompany VWF Antigen (VWF:Ag) assay.

METHODS

The aim of this study was to explore the correlation between VWF:Ag, VWF ristocetin cofactor activity (VWF:RCo) and FVIII in 213 consecutive patients undergoing screening for VWD.

RESULTS

Forty-six patients were identified with VWF:Ag levels lower than the diagnostic threshold (54 IU/dl). A significant correlation was observed between VWF:Ag and VWF:RCo (r = 0.892; p < 0.001), VWF:Ag and FVIII (r = 0.834; p < 0.001), VWF:RCo and FVIII (r = 0.758; p < 0.001). Receiver operating characteristic curve analysis of the VWF:Ag assay revealed an area under the curve of 0.978 and 0.957 for detecting life-threatening values of FVIII (<30 IU/dl) and VWF:RCo (<40 IU/dl), respectively. The negative and positive predictive values at the VWF:Ag threshold value of 54 IU/dl were 100% and 33% for detecting life-threatening FVIII deficiencies, 94% and 80% for identifying abnormal values of VWF:RCo.

CONCLUSIONS

Due to the excellent correlation between VWF:Ag and FVIII and to the diagnostic efficiency of VWF:Ag for identifying abnormal FVIII levels in patients with VWF deficiency, routine measurement of FVIII may not be necessary in the initial screening of patients with suspected VWD. However, the limited negative predictive value of VWF:Ag for identifying type 2 VWD does not allow to eliminate VWF:RCo or VWF:FVIIIB assays from the diagnostic workout.

Cell-derived microparticles and exosomes in neuroinflammatory disorders

All blood cells and the vascular endothelium shed microparticles (MP) from their plasma membranes when suitably stimulated, and assay of MP in patient blood has found increasing application to the monitoring of disease states. In addition, mounting evidence suggests that MP are not mere epiphenomena but play significant roles in the pathophysiology of thromboses, inflammation, and cancers. This chapter endeavors to summarize the limited number of studies thus far done on MP in neurological disorders such as multiple sclerosis (MS), transient ischemic attacks, and the neurological manifestations of antiphospholipid syndrome (APS). In addition, the chapter offers some plausible hypotheses on possible roles of MP in the pathophsyiology of these disorders, chiefly, the hypothesis that MP are indeed important participants in some neuropathologies, especially those which are ischemic in nature, but probably also inflammatory ones. The chapter also goes over the history and general principles of MP studies (e.g., assay methods and pitfalls), comparison with alternative methods (e.g., soluble markers of disease states), subclasses of MP (such as exosomes), and other topics aimed at helping readers to consider MP studies in their own clinical fields. Tables include a listing of bioactive agents known to be carried on MP, many of which were heretofore considered strictly soluble, and some of which can be transferred from cell to cell via MP vectors, for example certain cytokine receptors.

ADAMTS13 activity in sickle cell disease

Sickle red blood cell (SRBC)-endothelial adhesion plays a central role in sickle cell disease (SCD)-related vaso-occlusion. As unusually large von Willebrand factor (ULVWF) multimers mediate SRBC-endothelial adhesion, we investigated the activity of ADAMTS13, the metalloprotease responsible for cleaving ULVWF multimers, in SCD. ADAMTS13 activity was determined using a quantitative immunoblotting assay. VWF:Ag and VWF:RCo were determined using commercial assays. The high-molecular-weight VWF multimer percentage was determined by employing gel electrophoresis. ADAMTS13 activity was similar among asymptomatic patients (n = 8), patients at presentation with a painful crisis (n = 23), and healthy controls. ADAMTS13/VWF:Ag ratios were lower in patients compared to healthy HbAA controls, with the lowest values at presentation with a painful crisis (P = 0.02). Division of samples in those with VWF:RCo/VWF:Ag ratios < 0.70 and those with ratios >or= 0.70 revealed significantly more samples with ratios >or= 0.70 (P = 0.01) collected during painful crises. ULVWF multimers were detected in 6 patient samples and in 1 control sample. ADAMTS13/VWF:Ag ratios were inversely related to the duration of symptoms at presentation with an acute vaso-occlusive event (r(s)-0.67, P = 0.002). Although SCD is characterized by elevated VWF:Ag levels, no severe ADAMTS13 deficiency was detected in our patients.

Evaluation of a rapid automated assay for analysis of von Willebrand ristocetin cofactor activity

A commercially available turbidometric assay has been evaluated for the measurement of von Willebrand factor ristocetin cofactor activity (VWF:RCo). The assay is simple, rapid, and can be cost-effectively performed on automated coagulation analyzers. This study's aim is to illustrate the performance of the automated VWF:RCo assay and its capacity to identify patients with von Willebrand disease (VWD). By direct comparison with a conventional VWF:RCo assay, performed on an aggregometer, the concordance between the two assays was 96%. With minor modifications, the automated assay showed a detection level of 0.03 kIU/L with linearity to 2.00 kIU/L. The imprecision of the automated assay was reduced compared to the conventional assay procedure with CV of 6.8% at the 1.00 kIU/L level and 8.6% at the 0.30 kIU/L level. The automated VWF:RCo assay was also suitable as a screening test to detect VWD in patients investigated for the cause of an increased bleeding tendency. In this situation the automated VWF:RCo assay was tested simultaneously with an automated immunoassay for von Willebrand antigen. Receiver operating curves for the diagnosis of VWD showed a greater area under the curve for the automated VWF:RCo assay compared to the immunoassay, 0.98 vs. 0.94, although the difference did not reach significance. In conclusion, the modified automated VWF:RCo assay shows better precision, lower detection limit, is faster to perform with a lower cost per test compared to the conventional aggregometer based VWF:RCo activity method and is an alternative to an antigen immunoassay as a screening test for VWD.

Laboratory Diagnosis of von Willebrand Disorder: Use of Multiple Functional Assays Reduces Diagnostic Error Rates

Regular multilaboratory surveys of laboratories primarily in Australia, New Zealand, and Southeast Asia have been conducted over the past 8 years to evaluate testing proficiency in the diagnosis of von Willebrand disorder (VWD). We have reassessed the findings of these surveys with a particular emphasis on the diagnostic errors and error rates associated with particular tests or test panel limitations. The 37 plasma samples dispatched to survey participants include 9 normal samples, 4 type 1 VWD samples, 8 type 2 VWD samples (2A x 3, 2B x 3, 2M x 1, and 2N x 1), and 4 type 3 VWD samples. In addition to providing numerical test results, participant laboratories (average, n = 35) were asked to provide diagnostic interpretations of their test results regarding whether VWD was evident and, if so, the probable subtype. Although laboratories usually provided correct interpretative responses, diagnostic errors occurred in a substantial number of cases. On average, type 1 VWD plasma was misidentified as type 2 VWD plasma in 11% of cases, and laboratories that performed the ristocetin cofactor assay for von Willebrand factor (VWF:RCo) without performing the collagen-binding activity assay for VWF (VWF:CB) were 6 times more likely to make such an error than those that did perform the VWF:CB. Similarly, type 2 VWD plasma samples were misidentified as type 1 or type 3 VWD in an average of 20% of cases, and laboratories that performed the VWF:RCo without the VWF:CB were 3 times more likely to make such an error than those that performed the VWF:CB. Finally, normal plasma was misidentified as VWD plasma in an average of 5% of cases, and laboratories that performed the VWF:RCo without the VWF:CB were 10 times more likely to make such an error than those that performed the VWF:CB. We conclude that laboratories are generally proficient in their testing for VWD and that diagnostic error rates are substantially reduced when test panels are more comprehensive and include the VWF:CB.

Reliability and reproducibility of classification of children as "bleeders" versus "non-bleeders" using a questionnaire for significant mucocutaneous bleeding

The diagnosis of type 1 von Willebrand disease (VWD), the most common inherited bleeding disorder in humans, is greatly dependent on an accurate diagnosis of significant mucocutaneous bleeding. In a previous study, the authors modified the criteria of the International Society on Thrombosis and Haemostasis for significant mucocutaneous bleeding to a format, the Hospital for Sick Children (HSC) criteria, that was more applicable to diagnose significant mucocutaneous bleeding in children. To assess the reliability and reproducibility of classification of subjects as "bleeders" versus "non-bleeders" using a questionnaire for significant mucocutaneous bleeding targeted to children, 39 subjects interviewed for a previous HSC VWD study were reinterviewed for the current study. The original bleeding classification was confirmed in 80% of subjects interviewed for a second time, indicating that this method of classification is reproducible (kappa = 0.65), with a "substantial" agreement among the investigators who reviewed the questionnaire responses (kappa = 0.71). The validity and utility of the HSC questionnaire for primary screening of children with suspected mucocutaneous bleeding disorders merits assessment in further clinical studies.

Laboratory diagnosis of von Willebrand's disorder: quality and diagnostic improvements driven by peer review in a multilaboratory test process

Regular multilaboratory surveys of laboratories derived primarily from Australia, New Zealand and Southeast Asia have been conducted over the past 7 years to evaluate testing proficiency in the diagnosis of von Willebrand's disorder (VWD) and to assess changes to test practice. Participating laboratories (currently 45) are asked to perform their usual panel of tests for VWD, and then to self-interpret test results as to the likelihood (or not) of VWD, as well as to the potential subtype identified. Samples provided in the past two survey distributions (both conducted in 2003) were as follows. Survey part A/distribution 1: Normal donor plasma, plasma with borderline normal/reduced levels of VWF (x2) and plasma from an individual with type 2 A VWD. Survey part B/distribution 2 (family VWD study): Plasma from a father, mother and son with borderline normal/reduced von Willebrand factor (VWF), and a daughter with type 3 VWD. In line with previously published survey results, the interassay and within method coefficients of variation (CV) were similar for all assays (around 15-25%), although tending to be slightly higher for VWF:RCo and VWF:CB than VWF:Ag and FVIII:C. Most laboratories reported test values consistent with expected findings, and made correct interpretations or predictions regarding the nature of the samples, although discrepant assay results or interpretations are still seen in approximately 5-10% of responses (typically from laboratories using a more limited test panel or not performing the VWF:CB). Overall, problems with the non-identification of functional VWF discordance in type 2 VWD, the misidentification of functional VWF discordance in type 1 VWD, and difficulties in discriminating types 1 and 3 VWD appear to predominate. In comparison with previous surveys, performance of electro-immuno diffusion (EID) (or Laurel gel) procedures has now ceased, and a reduction in VWF:RCo and VWF:Multimer testing and an increase in latex immunoassay (LIA) testing is sustained. We conclude that laboratories are generally proficient in tests for VWD, and that diagnostic error rates are reduced when test panels are more comprehensive and include the VWF:CB.

Clinical application of the PFA-100

The PFA-100 (platelet function analyzer) is a relatively new tool for the investigation of primary hemostasis. Recent studies have shown its utility as a screening tool for investigating possible von Willebrand disorder (VWD) and various platelet disorders. More recently, the PFA-100 has been shown to be valuable in monitoring desmopressin acetate (DDAVP) therapy in both VWD and platelet disorders. The PFA-100 has also been evaluated in many other studies for its utility in assessing drug effects, for potential monitoring of antiplatelet medication (including aspirin), or for evaluation of overall primary hemostasis in various clinical disorders or during surgical procedures. This article reviews current findings and highlights the benefits and limitations of the clinical utility of the PFA-100. Ultimately, the greatest strengths of the PFA-100 are its simplicity of use and excellent sensitivity to particular hemostatic disturbances such as VWD, platelet disorders, and platelet-affecting medication. However, because it is thus a global test system, this also creates a significant limitation because the PFA-100 is not specific for, nor predictive of, any particular disorder. However, used appropriately, the PFA-100 can be considered a worthwhile addition to any hemostasis laboratory involved in the diagnosis or therapeutic monitoring of bleeding disorders and potentially of antiplatelet medication. This review should be valuable to both hemostasis scientists and clinical specialists.

Obstetric and gynaecological aspects of von Willebrand disease

The impact of von Willebrand disease in females is pronounced in terms of menorrhagia and postpartum haemorrhage. There is a very high proportion of von Willebrand disease patients with menorrhagia and associated anaemia, impairment of quality of life, including loss of time from work or school, and a high rate of the use of hysterectomy for ultimate control of the bleeding. The 'early' detection of von Willebrand disease in females may avert these complications. Consequently, there have recently been ongoing international efforts to determine the prevalence of von Willebrand disease in females presenting with menorrhagia, providing a prevalence of 7-20% combined from three studies including a total of 300 patients. Issues remain regarding the optimal dose/schedule of intranasal or subcutaneous desmopressin use for menorrhagia and the relative efficacy of anti-fibrinolytic agents. The proper role of oral contraceptives deserves further study in von Willebrand disease patients with menorrhagia as recent studies have paradoxically demonstrated a lower response rate in type 1 than type 2 or 3 von Willebrand disease. Despite the well-known adage of the 'gestational palliation' of von Willebrand disease, there is also a high proportion of postpartum haemorrhage in type 1 patients, especially after the 24 hour post-delivery period. This may occur despite a normalization of the factor VIIIc level in the third trimester, particularly in type 2 and 3 patients. The care-giver must be aware that haemorrhage can occur up to 5 weeks postpartum. In sum, studies over the past decade have documented a substantial impact of menses and childbirth on von Willebrand disease patients. These results should serve as a basis for interventional studies to reduce the morbidity of menstruation and childbirth.

Appropriate laboratory assessment as a critical facet in the proper diagnosis and classification of von Willebrand disorder

The correct diagnosis and classification of von Willebrand disease or disorder (VWD) is crucial because the presenting biological activity of von Willebrand factor (VWF) determines both the haemorrhagic risk and the subsequent clinical management. A variety of laboratory assays may be employed, not necessarily restricted to assessments of VWF. Because of assay limitations and von Willebrand disease heterogeneity, no single test procedure is sufficiently 'robust' to permit the detection of all VWD variants. Classically, the test panel might include any combination of: (a) skin bleeding time, (b) von Willebrand factor antigen assay, (c) factor VIII C level, (d) assessment of 'functional' von Willebrand factor (collagen-binding activity or ristocetin co-factor assay), (e) ristocetin-induced platelet aggregation, and (f) multimer analysis. There have also been many new diagnostic developments that have begun to influence the diagnostic process. These include the automation of existing assay procedures, new automated platelet function analyzers such as the PFA-100, and specific von Willebrand factor-factor VIII-binding assays. This chapter focuses on the recommended laboratory process for the investigation of VWD. The selection of an appropriate combination test panel and testing sequence is crucial for the proper diagnosis and classification of congenital von Willebrand disease.

Laboratory diagnosis of von Willebrand disorder (vWD) and monitoring of DDAVP therapy: efficacy of the PFA-100 and vWF:CBA as combined diagnostic strategies

We have coevaluated a combination of test processes for diagnosing von Willebrand disease (vWD) and monitoring deamino-delta-D-arginine vasopressin (DDAVP) therapy. Using normal controls (n = 23), closure time (CT) ranges measured by PFA-100(R) were (mean +/- 2SD): (i) collagen/ADP cartridge (C/ADP): 67-127 s (ii) collagen/epinephrine (C/Epi): 94-162 s. From a panel of 125 patients undergoing evaluation for clinical haemostatic defects, 29/30 samples from patients with vWD [17/18 type 1, 1/1 type 3, 3/3 type 2A, 7/7 type 2B and 1/1 pseudo-vWD] gave prolonged CTs using C/Epi. The C/ADP was less sensitive, being normal in 7/18 of the type 1 vWD individuals, with higher sensitivity to more severe vWD. Individuals with haemophilia (six factor VIII-deficient, one factor XI-deficient) gave normal CTs, while those with clinical thrombocytopenia (n=13) gave normal or prolonged CTs, somewhat dependent on platelet count. The PFA-100 was also evaluated as a part of the laboratory monitoring procedure in patients with either vWD or haemophilia undergoing a DDAVP trial as a therapeutic management process. For vWD, correction of an initially prolonged CT by DDAVP, accompanied by normalization of von Willebrand factor (vWF) measurable by von Willebrand factor antigen, vWF collagen binding activity and vWF ristocetin cofactor assays (vWF:Ag, vWF:CBA and vWF:RCof), was achieved in type 1 vWD (n=5). In an individual with type 2A vWD, DDAVP normalized vWF:Ag and vWF:RCof, but had no apparent effect on the baseline maximally prolonged CT. In an individual with type 2B vWD, factor VIII/vWF concentrate also normalized vWF:Ag and vWF:RCof, but similarly had no apparent effect on the baseline maximally prolonged CT. vWF:CBA did not normalize for either of these individuals, potentially suggesting that normalization of vWF:CBA might be required for normalization of CT. This concept is supported by correlation analysis undertaken between CT and various vWF parameters. Among these, vWF:CBA held the strongest relationship in our data set, which showed an inverse progressive rise in CT for falling vWF:CBA. Based on these results, we would conclude that the PFA-100 is highly sensitive to the presence of vWD, and may thus provide a valuable screening test for vWD. Furthermore, the combined utility of the PFA-100 and vWF:CBA as markers of DDAVP responsiveness may prove to be simple, quick but powerful, predictors for its clinical efficacy.

Utility of the PFA-100 for assessing bleeding disorders and monitoring therapy: a review of analytical variables, benefits and limitations

The PFA-100 (platelet function analyser) is a relatively new tool for the investigation of primary haemostasis. Recent studies have shown its utility in monitoring antiplatelet therapy (including aspirin) and as a screening tool for investigating possible von Willebrand disease (vWD) and various platelet disorders. More recently, the PFA-100 has been shown to be of value in monitoring DDAVP therapy in both vWD and platelet disorders. This paper reviews current findings, details the utility of the PFA-100 for some of these purposes, as well as reviewing analytical variables that may complicate the interpretation of results. The author highlights the benefits, as well as noting the limitations, of its use. Ultimately, the greatest strengths of the PFA-100 are its simplicity in use and excellent sensitivity to particular haemostatic disturbances such as vWD, platelet disorders and platelet-affecting medication. However, because it is thus a 'global' test system, this also creates a significant limitation, as the PFA-100 is not specific for, nor predictive of, any particular disorder. However, utilized appropriately, the PFA-100 can be considered a worthwhile addition to any haemostasis laboratory involved in the diagnosis or therapeutic-monitoring of bleeding disorders including vWD and platelet-dysfunctions. This review should be of value to both haemostasis scientists and clinical specialists.

Assessment of current diagnostic practice and efficacy in testing for von Willebrand's disorder: results from the second Australasian multi-laboratory survey

This study reports an evaluation of current laboratory practice for the diagnosis of von Willebrand's disorder (VWD) by means of a multi-laboratory (n = 19) survey (the 'Second Australasian VWD Survey'). Results are compared with a previously conducted but similarly comprehensive survey ('Survey-1'). Samples comprised a new set of seven plasmas: (i) Type 3 VWD; (ii) Type 2B VWD; (iii) Moderate Type 1 VWD/Haemophilia A combined defect; (iv) Normal individual; (v) Mild Type 1 VWD; (vi) Type 2M/2A VWD; (vii) Type 2N VWD. Overall, many current findings confirmed those reported in Survey-1 [including between-method analysis, within-method analysis, inter-laboratory assay variation, sensitivity to low levels of von Willebrand Factor (vWF), detection of functional vWF 'discordance', and appropriateness of diagnostic predictions]. Novel findings include: (i) although vWF:collagen binding activity (vWF:CBA) performed better than vWF:ristocetin cofactor (vWF:RCof) assay in identification of functional discordance in Type 2B VWD, both assays performed equally in identification of discordance in the Type 2M/2A VWD; (ii) most laboratories failed to identify the Type 2N VWD as a potential 2N utilizing vWF antigen (vWF:Ag) and factor VIII coagulant (FVIII:C) testing as a screening process; (iii) this particular survey was followed up by a dry workshop attended by over 45 scientists from Australia and New Zealand, and comprising representatives from most survey participants. Discussion covered many topics including the effect of blood group, the role (if any) of the bleeding time, the role of the PFA-100, confirmatory and additional tests, and the possibility of restricting testing to specialized centres. Consensus was reached on the following points: (i) diagnosis of VWD requires both clinical and laboratory assessment; (ii) testing should comprise FVIII:C, vWF:Ag and either/or both vWF:RCof and vWF:CBA; (iii) laboratory results should be reviewed in the light of clinical findings; and (iv) confirmatory repeat testing should be performed on a sample taken 6 weeks later.

Detection of von Willebrand disorder and identification of qualitative von Willebrand factor defects. Direct comparison of commercial ELISA-based von Willebrand factor activity options

Two von Willebrand factor (vWF):collagen binding (activity) assay (CBA) kit methods are commercially available. A monoclonal antibody (MAB)-based enzyme-linked immunosorbent assay (ELISA) system reported to correlate with a standard vWF:ristocetin cofactor (RCof) assay is also commercially available. It is marketed as a vWF:Activity assay and is available in 2 assay version formats. In the present study, these 4 vWF-activity options were compared directly with in-house vWF:CBA ELISAs for their ability to detect von Willebrand disease (vWD) and identify qualitative vWF defects. The 2 MAB-based systems detected vWD but could not specifically identify qualitative vWF defects, although the recently modified Mark II kit was more effective for the latter compared with the original Mark I kit. All vWF:CBA methods, including in-house and commercial, also effectively detected vWD but differed in their ability to identify qualitative vWF defects. Effectiveness was highest using the in-house reference vWF:CBA (using a type I/III collagen mix product from equine tendon), the Gradipore vWF:CBA (also uses equine tendon-derived collagen), or the in-house vWF:CBA methods using type III human collagen at a relatively low concentration (1 or 3 micrograms/mL, without covalent linkage). The IMMUNO vWF:CBA seemed to be the least effective among the vWF:CBA methods for detection of qualitative vWF defects.