von Willebrand Factor Antigen (Factor VIII:R Antigen) 

Updated: Nov 05, 2019
Author: Vadim Kostousov, MD; Chief Editor: Eric B Staros, MD 

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)

 

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 that is largely normal or mildly decreased, with vWF:RCo of less than 30-40% (vWF:RCo/vWF:Ag ratio < 0.7), is typical for vWD 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

 

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 regime to produce platelet-poor plasma

Storage: Up to 6 hours at +18-25°C or plasma sample should be frozen; specimen is stable for 1 month at -20°C; whole blood after collection should not be stored at refrigerator temperatures (+2°C to +4°C) owing to cold-induced binding of vWF to platelets and selective loss of vWF:Ag in plasma.[3]

 

Background

Description

vWF is a multimeric protein (molecular weight varies from 500-20,000 kDa) 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:Ag assay evaluates the total protein amount in plasma. The most common in clinical laboratories are latex immunoturbidimetric assays, in which the agglutination of latex microparticles coated with anti-vWF antibodies is proportional to vWF:Ag. Cloudy plasma may result in underestimation of vWF:Ag levels, while the presence of rheumatoid factor in the plasma can produce overestimation.

Indications/Applications

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

  • Diagnosis of vWD

  • Differentiation of vWD subtypes

  • Differentiation of vWD from hemophilia A

  • Monitoring therapy of vWD

Considerations

Repeated vWF:Ag and vWF:RCo activity testing is sometimes needed to identify low levels of vWF compatible with vWD. A retrospective study showed that about 30% of pediatric patients required a second vWD test before the diagnosis was established.[5] Other tests (vWF collagen-binding assay, vWF multimer analysis, genetic analysis) may also be useful in confirming the diagnosis.[4, 6, 7]  African Americans have vWF:Ag levels that are approximately 20% higher than those in the white population, although their vWF:RCo levels do not differ.[8]  In addition, vWF:Ag increases with age, both in healthy individuals and in those with vWD.[9, 10]

 

Questions & Answers