Impact-R CPA test can be a useful screening test for von Willebrand Disease.

Von Willebrand Disease or vWD is the most common hereditary bleeding disorder. It is caused by a deficiency in the von Willebrand Factor (vWF).  VWF has two main functions in the coagulation cascade: 1) it is the major adhesion molecule that anchors the platelets to the exposed subendothelium, and 2) it is the binding protein for Factor VIII (FVIII). The clinical manifestations of vWD is due to its effect on platelet function.

Patients with vWD present mostly with mucosal bleeding and sometimes with post-operative bleeding.  Signs and symptoms include: bruising in uncommon areas of the body, prolonged epistaxis, heavy menstrual bleeding or menorrhagia, prolonged bleeding at dental extraction sites, or during tonsillectomies.

VWD has 3 major types (Type 1, 2, and 3) with Type 2 having 4 subtypes (Type 2A, 2B, 2M, and 2N). The most common is Type 1. The following table compares the Activated Partial Thromboplastin Time (aPTT), vWF antigen, vWF activity, and FVIII activity of the different types.

Von Willebrand factor replacement is the definitive therapy for vWD especially as prophylaxis for major procedures to reduce the risk of post-operative bleeding. For minor procedures and for mild Type 1 vWD treatment of choice is 1-deamino-8-D-arginine vasopressin (DDAVP or desmopressin) which causes the release of vWF and FVIII from endothelial stores. It can be given intravenously or by an intranasal spray.

Diagnosis is done by careful history and physical exam with a combination of several laboratory tests such as aPTT, ristocetin cofactor assay, collagen binding activity multimer assays. A useful screening test to determine decreased platelet function is the IMPACT-R Cone and Platelet Analyzer (CPA) which tests platelet adhesion and aggregation in anti-coagulated whole blood under arterial flow conditions. This test is qualitative compared to the merely quantitative platelet count.