Endothelial cells with stored von Willebrand factor (red) in the cytoplasmic granules (Weibal-Palade bodies). University of California – San Diego Medical School.
	Prevalence of VWD
	VWD - Symptoms and Signs
	Hemophilia and VWD
	Bleeding Disorders
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Von Willebrand's Disease

Von Willebrand's Disease (VWD) is a group of genetic bleeding disorders in which the common clinical finding is a prolonged bleeding time. During recent years, evidence would seem to indicate that VWD is a variety of heterogeneous diseases in which the amount and/or function of von Willebrand factor (VWF), in plasma and/or platelets is abnormal, and the activity and concentration of plasma Factor VIII is lowered to varying degrees.

VWF is a plasma protein secreted by endothelial cells. Multimers of all sizes of VWF form complexes in plasma with factor VIII. These complexes are required to maintain normal plasma factor VIII levels.

Prevalence of VWD

VWD is the most common hereditary hemorrhagic disease in humans. However the true prevalence of VWD is difficult to establish as clinical manifestations of this disease vary and milder cases are often not recorded.

Research still continues on the inheritance of VWD and recent studies suggest that as many as 1 - 3% of the population may have this disorder. This figure contrasts strongly with the known incidence of VWD of 1 in 8000.

VWD - Symptoms and Signs

VWD can affect persons of either sex with a positive maternal or paternal history. Bleeding manifestations will be mild to moderate and include easy bruising, intermittent bleeding from small skin cuts over a prolonged period and abnormal bleeding after surgical procedures (e.g. tooth extraction).

Screening coagulation tests will reveal a long bleeding time and sometimes a slightly prolonged PTT reflecting a moderately reduced plasma factor VIII level.

The level of plasma VWF can be temporarily elevated by vasoactive stimuli induced by stress or exercise. Also hormonal changes associated with stress or pregnancy and an acute phase response to inflammation or infection stimulate increased synthesis of VWF, which also elevates VWF levels in plasma. Thus, in persons with mild VWD, plasma level variations may cause screening tests to be normal on some occasions and abnormal on others, making diagnosis difficult.

Hemophilia and VWD - Differential Diagnosis

People with mild hemophilia and hemophilia carriers may have factor levels in the range expected for VWD, but will have normal levels of VWF antigen (VWF Ag) and RISTOCETIN Cofactor Activity, an activity measure of VWF. People with VWD show variable reductions in factor VIII, VWF Ag and RISTOCETIN Cofactor Activity. It is therefore important that VWF Ag and RISTOCETIN Cofactor assays are performed whenever a low factor VIII is found to differentiate between hemophilia A and VWD.