von Willebrand factor: its function and its measurement in the laboratory.

von Willebrand factor (vWF) is a complex protein essential to normal haemostasis. It is vital to platelet adhesion in the high shear stress conditions encountered in the small blood vessels. Deficient overall levels of, or the presence of abnormally functioning variants of, vWF lead to the common bleeding disorder termed von Willebrand's disease. Laboratory investigation is aimed at both quantitative and qualitative investigation with a view to classification of the abnormality for each individual patient into a particular sub-type.