vWFRistocetin

vWFRistocetin is a term used in hematology to describe the functional interaction between von Willebrand factor (vWF) and the antibiotic ristocetin in laboratory assays that assess the activity of vWF. It is most closely associated with the ristocetin cofactor activity of vWF, often denoted as vWF:RCo, which measures how effectively vWF can mediate platelet agglutination in the presence of ristocetin.

Mechanism and interpretation

In the ristocetin-dependent assay, ristocetin induces a conformational change in vWF that enables it to bind to the platelet receptor glycoprotein Ib (GPIb). This interaction promotes platelet agglutination that can be quantified spectrophotometrically or visually. The resulting activity is compared to a normal reference plasma and is reported as a percentage or in international units. Low vWF:RCo activity suggests impaired vWF function and can indicate von Willebrand disease (VWD). Results are interpreted together with vWF antigen (vWF:Ag) levels and factor VIII activity to classify VWD types (e.g., type 1, type 2 variants) and to guide management.

Clinical use and limitations

The vWF:RCo assay is used to diagnose VWD, monitor therapy, and assess bleeding risk in patients with suspected or confirmed disease. It can be influenced by laboratory variables such as platelet count, hematocrit, and sample handling, as well as by medications or concurrent conditions that affect platelet function. Because ristocetin-based testing depends on both vWF and platelets, complementary tests (including RIPA, vWF:Ag, and factor VIII activity) are commonly used to achieve a comprehensive assessment.

History and nomenclature

Ristocetin was historically discovered as an antibiotic that, in laboratory tests, revealed the interaction between vWF and platelet GPIb. The term vWFRistocetin reflects the use of ristocetin in assays that evaluate vWF function, particularly the vWF:RCo activity measurement.