Standardization and comparison of nonautomated assays to measure the collagen binding activity of von Willebrand factor.

INTRODUCTION

Diagnosis of von Willebrand disease (VWD) is difficult due to the heterogenic phenotype of patients and to the complex tests that are required for an adequate investigation. The collagen binding assay (VWF:CB) reveals the adhesion capacity of von Willebrand factor (VWF) to collagen and can be useful to reduce the misleading diagnosis of VWD. This study aimed the standardization of 2 nonautomated VWF:CB assays based on ELISA and flow cytometry.

METHODS

Plasma samples from 87 patients previously diagnosed with VWD and 22 healthy controls were analyzed. Measurement of the VWF-collagen binding activity was performed using a commercial assay and the 2 tests proposed. VWF:CB/VWF:Ag ratio was calculated for samples and the differentiation between types 1, 2A, and 2M was analyzed.

RESULTS

ELISA and flow cytometry tests presented strong correlation with the gold standard test (r  = .8976 and r  = .8143, respectively). Tests based on ELISA and flow cytometry presented a bias of +7.2% and -3.6%, respectively.

CONCLUSION

The ELISA test demonstrated better performance to detect VWF-collagen binding activity in healthy individuals and VWD patients. This test could differentiate 2A and 2M subtypes using a feasible protocol that can be easily implemented.