VWFRistocetinFaktor

VWFRistocetinFaktor, or von Willebrand factor ristocetin cofactor activity (VWF:RCo), is a laboratory measure of the functional activity of von Willebrand factor (VWF) in promoting ristocetin-induced platelet agglutination. It reflects how effectively VWF can bind platelets via the glycoprotein GPIb in the presence of ristocetin.

The assay works by mixing patient plasma with a standardized source of platelets and ristocetin, then assessing the degree of platelet aggregation. The result is expressed as a percentage of normal pooled plasma (VWF:RCo%) or, less commonly, in international units per deciliter (IU/dL) relative to a reference standard. The VWF:RCo value provides an estimate of the functional activity of VWF, complementing measurements of VWF antigen (VWF:Ag).

Clinical relevance and interpretation rely on comparing VWF:RCo to VWF:Ag. A reduced VWF:RCo with relatively preserved VWF:Ag suggests a qualitative defect in VWF function (as seen in certain types of von Willebrand disease, VWD type 2). Severe reductions or near absence of VWF:RCo indicate a quantitative deficiency (VWD type 3). The ratio of VWF:RCo to VWF:Ag (often used in classification) helps differentiate VWD subtypes and guides management. VWF:RCo is also used alongside multimer analysis and bleeding history to assess bleeding risk and to monitor therapy with desmopressin or VWF-containing concentrates.

Limitations and pre-analytical factors can influence results. ABO blood group, platelet count, antifolate medications, aspirin or other antiplatelet drugs, and sample handling can affect VWF:RCo measurements, so results should be interpreted in context.