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HelpTest Code VWACT von Willebrand Factor Activity, Plasma
Ordering Guidance
This activity assay is most effective when it is combined with measurement of von Willebrand factor antigen and factor VIII coagulant activity, preferably as a panel of tests with reflexive testing and interpretive reporting. See AVWPR / von Willebrand Disease Profile, Plasma.
Additional Testing Requirements
Tests for F8A / Coagulation Factor VIII Activity Assay, Plasma and VWAG / von Willebrand Factor Antigen, Plasma are recommended in conjunction with this test (von Willebrand activity).
Specimen Required
Specimen Type: Platelet-poor plasma
Collection Container/Tube: Light-blue top (3.2% sodium citrate)
Submission Container/Tube: Plastic vial (polypropylene preferred)
Specimen Volume: 2 mL in 2 vials each containing 1 mL
Collection Instructions:
1. Specimen must be collected prior to factor replacement therapy.
2. For complete instructions, see Coagulation Guidelines for Specimen Handling and Processing.
3. Centrifuge, transfer all plasma into a polypropylene vial, and centrifuge plasma again.
4. Aliquot plasma (1-2 mL per aliquot) into 2 separate polypropylene vials leaving 0.25 mL in the bottom of centrifuged vial.
5. Freeze plasma immediately (no longer than 4 hours after collection) at -20° C or, ideally, ≤-40° C.
6. Send specimens in the same shipping container.
Additional Information:
1. Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results.
2. Each coagulation assay requested should have its own vial.
Useful For
Diagnosis of von Willebrand disease (VWD) and differentiation of VWD subtypes or differentiation of VWD from hemophilia A
Monitoring therapeutic efficacy of treatment with DDAVP (desmopressin) or VWF concentrates in patients with VWD
Reflex Tests
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| RIST | Ristocetin Cofactor, P | No | No |
Testing Algorithm
If von Willebrand factor activity is less than 55%, then the von Willebrand factor ristocetin cofactor activity assay will be performed at an additional charge.
Special Instructions
Method Name
Latex Immunoassay
Reporting Name
von Willebrand Factor Activity, PSpecimen Type
Plasma Na CitSpecimen Minimum Volume
0.5 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Plasma Na Cit | Frozen | 14 days |
Reject Due To
| Gross hemolysis | Reject |
| Gross lipemia | Reject |
| Gross icterus | Reject |
Clinical Information
von Willebrand factor (VWF) is a multimeric adhesive glycoprotein that is important for platelet-platelet and platelet-vessel hemostatic interactions. In addition, plasma VWF serves as a carrier protein for coagulation factor VIII, stabilizing its procoagulant activity. VWF circulates in the blood in 2 distinct compartments; plasma VWF mainly reflects VWF synthesis and release from vascular endothelial cells and platelet VWF (about 10% of the blood VWF) reflects VWF synthesis by bone marrow megakaryocytes with storage primarily in the alpha granules of circulating platelets. VWF antigen measurement assesses the mass of plasma VWF protein but does not reflect VWF functions or platelet VWF. The major function of VWF (mediating platelet-platelet or platelet-vessel interaction) is most commonly assessed by measurement of plasma ristocetin cofactor activity.
Patients with congenital severe type 3 von Willebrand disease (VWD) have markedly decreased or immeasurably low VWF antigen in the plasma (and in the platelets), and plasma VWF activity is very low or nondetectable. Patients with types 2A and 2B variants of VWD (with abnormal plasma VWF function and multimeric structure) may have normal or decreased plasma VWF antigen but typically have decreased plasma VWF activity and decreased higher molecular weight VWF multimers in the plasma. Patients with type 2M or type 2N VWD have normal levels of antigen, but either decreased VWF activity not caused by absence of higher molecular weight VWF multimers (type 2M VWD) or decreased factor VIII coagulant activity (type 2N VWD). Patients with type 1 VWD (with decreased but normally functioning plasma VWF) have concordantly decreased plasma VWF antigen and activity. Patients with acquired von Willebrand syndrome may have either normal or decreased plasma VWF antigen and decreased VWF activity.
Note: VWF activity measurement is most effective when it is combined with measurement of von Willebrand factor: VWF antigen and factor VIII coagulant activity, preferably as a panel of tests with reflexive testing and interpretive reporting (eg, AVWPR / von Willebrand Disease Profile, Plasma).
Reference Values
55-200%
Normal, full-term newborn infants may have mildly increased levels which reach adult levels by 90 days postnatal. Healthy, premature infants (30-36 weeks gestation) may have increased levels that reach adult levels by 180 days.
Note: Individuals of blood group "O" may have lower plasma von Willebrand factor (VWF) activity than those of other ABO blood groups, such that apparently normal individuals of blood group "O" may have plasma VWF activity as low as 40% to 50%, whereas the lower limit of the reference range for individuals of other blood groups may be 60% to 70%.
Interpretation
von Willebrand factor (VWF) activity is reduced in parallel with VWF antigen in von Willebrand disease (VWD), except in types 2A, 2B, and 2M, and some cases of acquired von Willebrand syndrome (AVWS) in which the VWF activity is disproportionately decreased relative to the level of VWF antigen.
The VWF activity may be decreased in congenital VWD or AVWS that may be associated with are variety of disorders including monoclonal gammopathies, lymphoproliferative disorders, autoimmune disorders, hypothyroidism, severe aortic stenosis, left ventricular assist device, and arteriovenous malformation.
The VWF activity may be increased in association with pregnancy or estrogen use (including oral contraceptives), acute (acute-phase reactant) or chronic inflammation, exercise or stress, liver disease, vasculitis, and thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS). Such increases in VWF activity may obscure the laboratory diagnosis of mild VWD.
Cautions
Measurement of von Willebrand factor (VWF) activity alone has limited diagnostic value. The diagnosis of von Willebrand disease requires a combination of clinical and laboratory information. VWF activity assay results generally must be used together with assays of VWF antigen and factor VIII coagulant activity for optimum clinical utility and diagnostic efficiency.
Results may be affected by:
-Unfractionated heparin >4.0 U/mL; may cause an overestimation of the test result
-Hemoglobin >70 mg/dL; may cause the result to be underestimated
-Bilirubin >4.2 mg/dL; may cause the result to be underestimated
-Triglycerides >1020 mg/dL; may cause the result to be underestimated
-Rheumatoid factor >200 IU/mL; may cause an overestimation of the test result
Specimens from patients who have received preparation of mouse monoclonal antibody for diagnosis or therapy may contain human antimouse antibody (HAMA). The presence of HAMA may cause an overestimation of results in immunoassays that utilize mouse monoclonal antibodies. This assay contains a blocking agent against HAMA to minimize this interference.
Method Description
This is a latex particle-enhanced immunoassay to quantify von Willebrand factor (VWF) activity in plasma. The activity of VWF is determined by measuring the increase of turbidity produced by the agglutination of the latex reagent. A specific anti-VWF monoclonal antibody adsorbed onto the latex reagent, directed against the platelet-binding site of VWF (glycoprotein Ib receptor), reacts with the VWF of patient plasma. The degree of agglutination is directly proportional to the activity of VWF in the sample and is determined by measuring the decrease of transmitted light caused by the aggregates.(Package insert: HemosIL von Willebrand Factor Activity. Instrumentation Laboratory Company; 12/2020)
Day(s) Performed
Monday through Saturday
Report Available
1 to 3 daysPerforming Laboratory
Mayo Clinic Laboratories in Rochester
Test Classification
This test has been modified from the manufacturer's instructions. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
85397
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| VWACT | von Willebrand Factor Activity, P | 68324-3 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| VWACT | von Willebrand Factor Activity, P | 68324-3 |