Evaluation of a new turbidimetric assay for von Willebrand factor activity useful in the general screening of von Willebrand disease

Abstract

We evaluated a new assay (HemosIL™VWF Activity on ACL-Futura) in the screening of VWD. Samples from healthy donors and previously diagnosed VWD patients were blindly analyzed by this new activity assay and standard VWF:RCo. Results agreed and both assays showed a similar sensitivity for the screening of VWD. Haematologica 2007; 92:5: 712-713 Von Willebrand disease (VWD), the most frequent inherited bleeding disorder, is caused by a deficiency and/or abnormality of the von Willebrand factor (VWF).1,2 The revised classification of VWD identifies two major categories, characterized by quantitative (types 1 and 3) or qualitative (type 2) VWF defects.2 The most common test of VWF activity, the assay of VWF:RCo together with VWF:Ag is traditionally considered the first step in the diagnosis of VWD, with the VWF:RCo/Ag ratio being recommended to discriminate type 1 from type 2A, 2B and 2M VWD.1,2 Given the complexities of the aggregometric test, several alternative laboratory methods have been proposed to measure VWF activity. Monoclonal antibody-based ELISA, 3,4Elisa-based VWF:RCo, 5,6 rapid assays for VWF:RCo using coagulometers, 7 and assays measuring the binding of VWF to collagen.8 The aim of this study was to evaluate the novel fully automated HemosIL™VWF Activity assay on the ACL-Futura automated coagulometer (Instrumentation Laboratory) as a potential screening test for the diagnosis of VWD.9,10 The assay uses latex sensitized with monoclonal antibodies (RFF VIII:R/1) 3 directed against the platelet binding site of VWF (GPIb receptor). The activity of VWF is determined by measuring the increase of turbidity produced by the agglutination of the latex particles as a consequence of the interaction between the GPIb receptor of VWF and the monoclonal antibodies. The lower limit of linearity has been reported at 12.5IU/dL. 9 A set of 57 normal controls and 70 VWD patients from two Hemophilia Centers were blindly analyzed in the R&D laboratory of Biokit with HemosIL™VWF:Ag, HemosIL™VWF Activity and VWF:RCo (Dade Behring) performed on an optical aggregometer. All methods were used to analyze samples which were then classified as normal or VWD type 1, 2, or 3 using the same criteria in both activity assays. The cut-off declared by the HemosIL based on ABO group was used to define normality or VWD, and the Activity/Antigen (Act/Ag) ratio was used to define quantitative (type 1) or qualitative (type 2) VWD using 0.7 as cut-off.1 Sample values below detectability were classified as type 3.After classification and database lock, blindness was disclosed by the two Hemophilia Centers where the patient samples were classified according to the clinical and laboratory findings. Table 1 shows the mean VWF concentration in IU/dL±SD (standard deviation) obtained for each assay. The first column shows the Classification according to the Haemophilia Centers. Nine samples from the Vicenza group which correspond to type 1 according to the last classification scheme, 2 are shown separately. The last columns show the mean Act/Ag ratio...

An international collaborative study to compare different von Willebrand factor glycoprotein Ib binding activity assays: the COMPASS‐VWF study

“…As expected, and also reported by others, all of the new assays (i.e. VWF:GPIbR by the HemosIL latex agglutination assay and the HemosIL AcuStar assay , the VWF:GPIbM Siemens assay and the VWF:Ab assay ) performed well and yielded results close to the old reference standard VWF:RCo. Although statistically significant and consistent in all participating laboratories, the slightly steeper regression lines for the VWF:Ab and VWF:GPIbM were clinically insignificant.…”

Evaluation of an Automated von Willebrand Factor Activity Assay in von Willebrand Disease

“…2,13 Results from VWF:Act assay have previously been shown to be well correlated with those of the standard VWF:RCo assay in all type 1 and 2 VWD variants. 7 Our retrospective study of 111 patients with well-identified VWD subtypes confirmed that VWF:RCo and VWF:Act are similar and well correlated. However, for certain patients, the results were very discordant with some cases of type 2M VWD being associated with normal VWF:Act.…”

Comparison of von Willebrand factor (VWF) activity levels determined by HemosIL AcuStar assay and HemosIL LIA assay with ristocetin cofactor assay by aggregometry

“…The ristocetin‐dependent AcuStar assay is more sensitive to type 2 VWD than the ristocetin‐independent HemosIL LIA assay. It is also not influenced by rheumatoid factor (up to 800 units per mL), which can result in falsely high readings for LIA antigen and functional assays . The presence of anti‐mouse antibodies can also cause falsely high results in some antibody‐based assays , but in another case report, VWF:RCo[Acu] seemed less affected than some other assays .…”