A Comparative Evaluation of an Automated Functional Assay for Von Willebrand Factor Activity in Type 1 Von Willebrand Disease

Abstract

Background

von Willebrand factor ristocetin cofactor activity (VWF:RCo) is the standard functional assay used for von Willebrand disease (VWD) diagnosis. However, it has some drawbacks including being time consuming and labor intensive and having high inter-laboratory variability. The HemosIL VWF activity assay has the advantages of both high speed and automation. The purpose of this study was to prospectively compare these two functional assays for type 1 VWD detection.

Methods

Plasma samples from 108 subjects were assessed in this study. HemosIL VWF activity was measured with the HemosIL latex immunoturbidimetric commercial kits by the ACL TOP coagulation analyzer. VWF:RCo was measured by platelet aggregation method. Pearson correlation analyses were performed to estimate the correlation of HemosIL VWF activity with VWF:RCo. Receiver-operator characteristic (ROC) curve analysis was used to evaluate the performance of the two diagnostic tests.

Results

The correlation coefficient between VWF:RCo and HemosIL VWF activity was 0.874 overall and was 0.761 and 0.811 in the cohorts of type 1 VWD and non-VWD, respectively. The sensitivity and specificity of HemosIL VWF activity assay for type 1 VWD identification were 94.7% and 80.0%, respectively, and the ROC curve of HemosIL VWF activity was larger than that of VWF:RCo (0.928 vs 0.863, p=0.0138). Finally, the positive and negative predictive values of the HemosIL VWF activity assay for type 1 VWD detection were 72.0% and 96.6%, respectively.

Conclusion

Our results demonstrate that the HemosIL VWF activity assay was an effective method for type 1 VWD screening and diagnosis. It carried good sensitivity and specificity and had a higher ROC curve than VWF:RCo besides showing good correlation with VWF:RCo. With its advantages of greater speed and automated performance, these results suggest that the HemosIL VWF activity assay was reliable and precise in the clinical setting.

Keywords:

• von Willebrand factor antigen
• von Willebrand disease
• VWF ristocetin cofactor activity
• VWF:RCo
• HemosIL VWF activity

Acknowledgments

The authors would like to thank Dr. Vivek R. Sharma, Research Scientist and Medical Director, at the Adult Hemophilia Program, Division of Medical oncology/Hematology, University of Louisville, School of Medicine, for his critical review of this manuscript. We would further like to thank the research assistant, Ms. Ya-Fang Yang for her skillful performance of laboratory assays and the study nurses for their hard work and diligence in compiling patients’ blood samples and study records.

Disclosure

The authors report no conflicts of interest in this work.

Additional information

Funding

This work was supported by the Tri-Service General Hospital Research Funds TSGH-C98-038.