Laboratory diagnosis of von Willebrand's disease.

The laboratory diagnosis of von Willebrand's disease (vWD) has become much more difficult because of the identification of numerous variant forms of vWD. The biologic and pathologic variability in individual patients necessitates a comprehensive assessment. Patients with classic type I vWD may be easily identified by using the bleeding time, activated partial thromboplastin time, platelet count, von Willebrand antigen, and ristocetin cofactor tests. In patients with variant forms of vWD, however, multimeric analysis of both platelet and plasma von Willebrand factor may be necessary. Furthermore, more than one assessment may be needed to detect an abnormal result in many of the aforementioned tests.