Factor V Assay 

Updated: Jan 16, 2014
  • Author: Bishnu Prasad Devkota, MD, MHI, FRCS(Edin), FRCS(Glasg), FACP; Chief Editor: Eric B Staros, MD  more...
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Reference Range

Factor V is a large glycoprotein with a molecular weight of 330,000 Daltons and has a plasma half-life of about 12 hours, with some reports of a half-life of up to 36 hours. [1] It functions as a cofactor in converting factor II to active factor II. It is proteolyzed by protein C/S complex. [2]

The reference range for factor V is as follows:

  • 70-150% of normal [2]
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Interpretation

Factor V is decreased in the following congenital conditions:

  • Inherited autosomal deficiency
  • Bleeding in homozygotes

Factor V is also decreased in the following acquired conditions:

  • Liver disease
  • Pathological fibrinolysis
  • Disseminated intravascular coagulation (DIC)
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Collection and Panels

See the list below:

  • Specimen: Plasma
  • Container: Blue-top vacuum tube
  • Collection method: Routine venipuncture

All samples must be sent in a sealed, leak-proof container marked with a biohazard sticker to comply with Occupational Safety and Health Administration (OSHA) safety standards.

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Panels

See the list below:

  • Quantitative functional assays of coagulation factors
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Background

Description

Factor V is a large glycoprotein with a molecular weight of 330,000 Daltons and has a plasma half-life of about 12 hours, with some reports of a half-life of up to 36 hours. [1] It functions as a cofactor in converting factor II to active factor II. It is proteolyzed by protein C/S complex. [2]

Factor V deficiency has been called parahemophilia because hemarthrosis may occur with severe deficiency of factor V. This also increases the bleeding time. [3] It is also called Owren disease after Dr Paul Owren, who identified the defect first and published it in Lancet in 1947. [4]

The gene for factor V is located on chromosome 1. Factor V circulates in plasma as a single-chain molecule. Platelets contribute approximately 20% of the factor V present in whole blood, with nearly all of it in granules. [5] Activated platelet factor V is also more resistant to inactivation by activated protein C. [6, 7] Platelet factor V appears to be sufficient for hemostatic function, at least in mice. [8]

Factor V is believed to be primarily activated by thrombin in vivo, although it can be activated by factor Xa as well. [9] Factor Xa appears to be the preferred activator of factor V released from platelet granules. [6] A common Arg 506 Gln mutation in factor V leads to resistance to inactivation by activated protein C (factor V Leiden) and is associated with an increased risk of venous thromboembolism. [10] Disruption of the factor V gene leads to either intrauterine death or death from massive bleeding within 2 hours of birth in experimental animals (mice). [11]

Factor V has anticoagulant and procoagulant properties. It enhances the anticoagulant action of activated protein C against factor VIIIa in a reaction in which protein S acts synergistically with factor V. [12, 13] Evidence from patients with inhibitors and deficiencies of plasma and platelet factor V indicates that platelet-derived factor V has an important role in hemostasis. [14, 15] Platelets undergo microvesiculation when activated, and the microvesicles, which are rich in factor V, are potent promoters of coagulation. [14]

Indications/Applications

When deficiency of factor V is suspected

Considerations

Factor V Leiden is a completely different inherited disorder in which factor V is mutated in a specific gene, which results in a hypercoagulable state. The mutation is very common, occurring in 5% of the US population. Factor V activity levels in patients with factor V Leiden are usually normal. [16]

Limitations of the test include partially clotted specimens due to poor mixture of anticoagulant (3:2 sodium citrate as per manufacturer’s blue topped tube), overfilled or underfilled test tubes altering the ratio of blood to anticoagulant (9:1), improperly stored plasma, contamination with heparin or dilution of collected sample if indwelling catheters are used or analytical errors such as lipemic, icteric, or hemolyzed plasma, which may interfere with photoelectric measuring instruments. [2]

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