tionally, vWF binds GP IIb/IIIa. There are three primary levels of vWD: type 1, type 2, and type 3. Seventy percent of all individuals with vWD have the type 1 disorders characterized by an abnormal bleeding time and an increased PTT in most patients. Type 2 vWD is the result of a qualitative defect of wVF, and type 3, the rarest type, is characterized by a total absence of vWF multimers and is autosomal recessive in its presentation. Type 2 vWD has many subtypes: type 2A, type 2B, type 2M, and type 2N. See Table 16-4 for a description of vWD and its variants. The vWF protein can be measured by several methods; those that assess its role in adhesion, its secondary role in aggregation, and its role in clotting factor activity. Ristocetin co-factor activity is the single best predictive assay17 and relies on the use of reagent platelets rather than patient's platelets during ristocetin-induced aggregation studies. Table 16.3 gives a description of a typical testing profile for vWD.

Treatment is usually tailored to the particular type or subtype of vWD. Some of the products that may be considered are desmopressin acetate (DDAVP), which causes the release of endothelial vWF. DDAVP may be given as an injectable agent or as a nasal spray, which makes it portable and convenient. For patients who are nonresponsive, vWF can be raised by giving high purity factor 8 products that contain a sufficient amount of vWF.

Bernard Soulier Syndrome

Bernard Soulier syndrome (BSS) is a rare adhesion defect of platelets that involves the GP Ib/IX complex. Once an injury has occurred, vWF acts as a medium through which the platelet membrane GP Ib has a receptor that allows its binding to collagen. As indicated

Table 16.4

Primary von Willebrand's Disease Derivatives*

Table 16.3

Basic Test Profile

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