Willebrand Factor

Overview

Von Willebrand factor (VWF) is a large multimeric glycoprotein involved in hemostasis that mediates platelet adhesion to damaged endothelium and serves as a carrier protein for coagulation factor VIII in plasma. It is synthesized primarily by endothelial cells and megakaryocytes and stored in Weibel‑Palade bodies and platelet α‑granules. Elevated VWF levels can indicate endothelial activation or damage, inflammation, or increased thrombotic risk, whereas markedly reduced levels are characteristic of von Willebrand disease and can cause mucocutaneous bleeding. Clinically, VWF measurement helps diagnose and classify von Willebrand disease, assess bleeding risk, and evaluate certain thrombotic or inflammatory conditions. It is also useful for monitoring responses to therapies such as desmopressin and VWF‑containing concentrates.

Clinical Use Cases

  • Diagnosis and subtyping of von Willebrand disease
  • Evaluation of unexplained mucocutaneous bleeding, easy bruising, or menorrhagia
  • Assessment of bleeding risk before surgery or invasive procedures in patients with suspected VWF abnormalities
  • Monitoring response to desmopressin (DDAVP) or VWF/FVIII concentrate therapy
  • Evaluation of endothelial activation or injury in conditions such as sepsis, thrombotic microangiopathies, and cardiovascular disease
  • Research biomarker of endothelial dysfunction and thrombosis risk in epidemiologic and clinical studies

Specimen Types

  • Citrated plasma (platelet‑poor plasma from venous blood)
  • Occasionally, platelet‑rich plasma or whole blood for specialized research assays

Measurement Methods

  • VWF antigen (VWF:Ag) by immunoassay (e.g., ELISA, latex immunoturbidimetric assay)
  • VWF activity assays (e.g., ristocetin cofactor activity [VWF:RCo], VWF:GPIb binding assays)
  • Collagen‑binding assay (VWF:CB)
  • Multimer analysis by gel electrophoresis to assess multimer distribution
  • Factor VIII coagulant activity (FVIII:C) in conjunction with VWF testing
  • Genetic testing of VWF gene for definitive subtyping in selected cases

Test Preparation and Influencing Factors

  • Acute stress, exercise, infection, inflammation, and surgery can transiently increase VWF levels.
  • Pregnancy and estrogen therapy (e.g., oral contraceptives, hormone replacement) may elevate VWF.
  • Blood type influences baseline VWF; individuals with blood group O often have lower VWF levels.
  • Sample collection issues (incorrect citrate ratio, under‑ or over‑filling, delayed processing, improper centrifugation) can affect results.
  • Recent transfusion of plasma products or VWF‑containing concentrates may alter measured levels.
  • Age and certain chronic conditions (e.g., liver disease, cardiovascular disease) can modify baseline VWF concentrations.

Synonyms

  • Von Willebrand factor
  • VWF
  • Factor VIII–related antigen (historical)
  • Ristocetin cofactor (when referring to VWF activity assay)

Further Reading