von Willebrand Factor Antigen (Factor VIII:R Antigen) 

Updated: Jun 23, 2014
  • Author: Vadim Kostousov, MD; Chief Editor: Eric B Staros, MD  more...
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Reference Range

Reference ranges are as follows [1, 2] :

  • Newborn < 6 mo: 60-190% (blood type O); 75-230% (non-O blood type)
  • Children 1-10 years: 50-150% (blood type O); 60-160% (non-O blood type)
  • Adults: 60-160% (blood type O); 70-200% (non-O blood type)
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Interpretation

von Willebrand factor (vWF) deficiency – Inherited (von Willebrand disease [vWD])

Type 1 vWD: Decreased vWF antigen (vWF:Ag) and vWF ristocetin cofactor (vWF:RCo) levels (vWF:RCo/vWF:Ag ratio >0.7)

Type 2 vWD: vWF:Ag is largely normal or mildly decreased, while vWF:RCo less than 30-40% (vWF:RCo/vWF:Ag ratio < 0.7) is typical for vWD types 2A and 2B

Type 3 vWD: Severe deficiency or absence (both vWF:Ag and vWF:RCo < 5%)

vWF deficiency – Acquired (acquired vWD or von Willebrand syndrome)

Due to autoimmune clearance or inhibition, as follows:

  • Lymphoproliferative diseases (lymphoma, leukemia)
  • Monoclonal gammopathies (multiple myeloma, Waldenstrom macroglobulinemia)
  • Systemic lupus erythematosus and other autoimmune disorders
  • Some cancers (Wilms tumor, Ewing sarcoma, carcinoma)

Due to increased shear-induced proteolysis (vWF:Ag is often normal or even elevated), as follows:

  • Ventricular septal defect
  • Aortic stenosis
  • Primary pulmonary hypertension
  • Extracorporeal life support
  • Due to other or unknown mechanisms, as follows:
  • Hypothyrosis
  • Drug-induced (hydroxyethyl starch, valproic acid)
  • Myeloproliferative diseases (polycythemia, thrombocythemia)
  • Angiodysplasia, glycogen storage disease

Increased vWF:Ag level and vWF:RCo activity are observed in acute phase reactions, as follows:

  • Stress and extensive exercise
  • Inflammation
  • Cancer
  • Obesity
  • Postoperative period
  • Diabetes
  • Atherosclerosis and atherothrombosis
  • Pregnancy
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Collection and Panels

Specimen: Citrated plasma

Collection: Tube with sodium citrate 3.2% citrate, blue top

Centrifugation: 2000-2500 g for 15 min or similar regimen to produce platelet-poor plasma

Storage: Up to 6 hours at +18-25C° or plasma sample should be frozen; specimen is stable for one month at -20C°; whole blood after collection should not be stored at refrigerator (+2C° to +4C°) owing to cold-induced binding von Willebrand factor (vWF) to platelets and selective loss of vWF antigen (vWF:Ag) in plasma. [3]

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Background

Description

von Willebrand factor (vWF) is multimeric protein (molecular weight varies from 500-20,000 kd) that is assembled from identical monomers in endothelial cells and megakaryocytes and can be released from endothelium and platelets upon activation. The half-life of vWF is approximately 12 hours (range, 9-15 h), and its clearance is faster in persons with blood type 0. [4] The main function of vWF is to support platelet adhesion to injured subendothelium in order to form a hemostatic plug. In addition, vWF is a carrier protein for factor VIII and prevents its proteolytic degradation in plasma.

The vWF antigen (vWF:Ag) assay evaluates the total protein amount in plasma. The most common in clinical laboratories are latex immunoturbidimetric assays for which the agglutination of latex microparticles coated with anti-vWF antibodies is proportional to vWF:Ag.

Indications/Applications

vWF:Ag (in conjunction with vWF ristocetin cofactor [vWF:RCo] and factor VIII activity) is indicated for the following:

  • Diagnosis of von Willebrand disease (vWD)
  • Differentiation of vWD subtypes
  • Differentiation of vWD from hemophilia A
  • Monitoring therapy of vWD

Considerations

Lipemic specimens may result in an underestimated vWF level.

A specimen with rheumatoid factor may result in an overestimated vWF.

Repeated vWF:Ag and vWF:Rco activity testing is sometimes needed to identify low levels of vWF compatible with vWD. Other tests (vWF collagen-binding assay, vWF multimer analysis, genetic analysis) might be useful to confirm the diagnosis. [4, 5, 6]

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