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Company
Immunology & Autoimmune
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Currently under review
Pending specialist review and validation.
This test measures how well von Willebrand factor in your blood helps platelets stick together in the presence of ristocetin. It reflects the functional activity of von Willebrand factor, a protein that works with platelets to start clot formation. Laboratories may list this test alongside factor eight testing because the two proteins are closely linked in the clotting system.
A preliminary result is an early functional snapshot released quickly while more specific or confirmatory assays may still be pending. It helps your clinician screen for problems and decide what additional testing is needed.
Your clinician may order this test if you have easy bruising, nosebleeds, heavy menstrual bleeding, or bleeding after dental work or surgery. It is a key part of evaluating for von Willebrand disease, the most common inherited bleeding disorder, and can help show whether the protein is working as it should.
The result helps guide next steps, such as additional tests to define the pattern of dysfunction and to plan treatment. It is often ordered together with von Willebrand factor antigen, factor eight activity, and sometimes specialized tests. It can also help assess response to treatments such as desmopressin or von Willebrand factor concentrates, especially before planned procedures.
A lower than expected activity suggests that von Willebrand factor is not functioning normally, which can contribute to a tendency to bleed. A result in the expected range is reassuring, but it does not rule out all forms of von Willebrand disease, so your clinician may pair it with other tests for a fuller picture.
Levels can change with stress, illness, inflammation, pregnancy, and aging. If a result is borderline or does not match your bleeding history, repeat testing when you are well and not acutely stressed may be recommended. Talk with your clinician about what your result means for you; they may suggest confirmatory testing, referral to a hematology specialist, and a plan for procedures or treatment if needed.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
This assay requires a properly filled sodium citrate tube and prompt processing. Underfilling, clotted or hemolyzed samples, delayed separation, freeze thaw cycles, or extreme shipping temperatures can falsely lower activity.
Von Willebrand factor is an acute phase reactant. Stress, exercise, infection, inflammation, and recent surgery can increase activity, while recovery from illness may change levels over time.
People with blood group O often have lower baseline von Willebrand factor. Age and pregnancy tend to increase levels, which can influence interpretation of a single measurement.
Desmopressin and von Willebrand factor concentrates can raise activity temporarily. Estrogen therapy may increase levels. Recent transfusion, cryoprecipitate, or infusion of clotting products can alter results.
Thyroid disease, liver disease, kidney disorders with protein loss, autoimmune conditions, and certain heart valve problems can cause acquired changes in von Willebrand factor function.
Testing during active bleeding, soon after surgery, or after receiving hemostatic treatment may not reflect your usual baseline and can warrant repeat testing later.
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