Laboratory testing for von Willebrand disease: toward a mechanism-based classification

Evaluation of a new commercial method for von Willebrand factor multimeric analysis

INTRODUCTION

Evaluation of von Willebrand factor (VWF) multimeric distribution is useful for subclassification of von Willebrand disease (VWD). Multimer analysis has historically been a manual, labor-intensive laboratory-developed test. The first commercial method for multimeric analysis was recently developed that utilizes a single instrument for gel electrophoresis, staining, and densitometry. The current study was undertaken to evaluate the performance characteristics of the new commercial method.

METHODS

Studies performed with the commercial method included evaluation of accuracy (method comparison), reference intervals (establishment of normal migration patterns in normal donor specimens), precision (multimer pattern reproducibility), and analytical sensitivity.

RESULTS

In the method comparison studies, concordant interpretations were obtained in 19 of 24 comparisons, including normal and abnormal specimens. The 5 specimens with discordant interpretations all involved slight differences and none were considered clinically significant. Thirty-eight normal donor specimens demonstrated normal multimer patterns. Multimer pattern reproducibility was demonstrated in normal and abnormal controls tested on each gel. In the sensitivity studies, adequate visualization of multimers was determined to require VWF protein concentrations of approximately 5%-10% of normal.

CONCLUSION

The commercial multimer method is a streamlined test that demonstrates comparable performance characteristics to our current laboratory-developed method and that provides the advantage of both electrophoresis gels and densitometry scans to aid interpretation.

Rituximab effectiveness in a patient with juvenile systemic lupus erythematosus complicated with acquired Von Willebrand syndrome

The acquired von Willebrand Syndrome (AvWS) is a bleeding disorder with laboratory findings similar to those of the congenital form. Its presentation is more common in adults than in children and is mainly associated with lymphoproliferative and myeloproliferative diseases and rarely with autoimmune diseases including systemic lupus erythematosus (SLE). Here, we report the case of a girl with SLE and AvWS with mucosal bleeding and low plasma levels of von Willebrand factor and factor VIII (FVIII) with failure to respond to treatment with first- and second-line therapies. The patient finally responded to rituximab. To our knowledge this is the first reported case of SLE associated with AvWS, that responded to rituximab.

Clinical measurement of von Willebrand factor by fluorescence correlation spectroscopy

BACKGROUND

Identification of von Willebrand factor (vWF) abnormalities in a variety of conditions is hampered by the limitations of currently available diagnostic tests. Although direct multimer visualization by immunoelectrophoresis is a commonly used method, it is impractical as a routine clinical test. In this study, we used a biophysical analysis tool, fluorescence correlation spectroscopy (FCS), to measure vWF distributions. The goals were to develop a method that is quicker and simpler than vWF gel electrophoresis and to evaluate the potential of FCS as a clinical diagnostic technique.

METHODS

We analyzed plasma from 12 patients with type 1 von Willebrand disease (vWD), 14 patients with type 2 vWD, and 10 healthy controls using a fluctuation-based immunoassay approach.

RESULTS

FCS enabled identification and proper classification of type 1 and type 2 vWD, producing quantitative results that correspond to qualitative gel multimer patterns. FCS required minimal sample preparation and only a 5-min analysis time.

CONCLUSIONS

This study represents the first implementation of FCS for clinical diagnostics directly on human plasma. The technique shows potential for further vWF studies and as a generally applicable laboratory test method.