The von Willebrand factor antigen (vWF:Ag) test measures the amount of von Willebrand factor protein in blood. It helps diagnose von Willebrand disease and other bleeding disorders, evaluates unexplained bruising or prolonged bleeding, and guides treatment. Low levels suggest von Willebrand disease or platelet function problems; high levels may reflect inflammation, pregnancy, or cardiovascular disease. Results are interpreted with clinical context and other coagulation tests.

The diagnostic assay panel for von Willebrand disease includes vWF antigen (vWF:Ag) to measure protein level, vWF activity assays (ristocetin cofactor or GPIb binding) to assess function, and vWF multimer analysis to evaluate multimer structure. Factor VIII activity is measured because vWF stabilizes FVIII. Platelet function tests (e.g., PFA‑100) and targeted genetic testing may be used for subtype classification.

Elevated von Willebrand factor (vWF) antigen means there is more vWF protein in the blood, often reflecting endothelial activation or damage and systemic inflammation. It can occur with infection, pregnancy, estrogen therapy, liver disease, or acute stress. Higher vWF can increase clotting risk and signals endothelial dysfunction, but isn’t diagnostic alone; further evaluation (coagulation studies and clinical correlation) is usually needed.

A normal von Willebrand factor antigen (vWF:Ag) level is generally about 50–150% (roughly 50–150 IU/dL). Laboratories may report results in IU/mL or percentages and reference ranges can vary slightly. Levels below ~50% suggest von Willebrand disease, while higher values may reflect acute-phase reactions, pregnancy, or blood group influences. Interpret results using the lab’s specific reference range and clinical context.

Low von Willebrand antigen means reduced von Willebrand factor, a protein needed for platelet adhesion and to stabilize factor VIII. It can indicate von Willebrand disease (mild to severe) or an acquired reduction. Symptoms include easy bruising, mucosal or prolonged bleeding. Further functional testing and hematology referral help confirm diagnosis and determine appropriate treatment based on severity.

Costs vary by country and setting: in the United States a VWF antigen test commonly ranges roughly $50–$200 out-of-pocket; in private UK labs about £30–£120 (testing is free on the NHS for eligible patients); in India typical private lab prices are around ₹400–₹1,500. Final cost depends on location, lab, whether it’s bundled with other coagulation tests, and insurance or public coverage.