Factor V Leiden (FVL)

Coagulation

Description

Factor V Leiden (FVL) results from a mutation in the factor V gene (c.1691G>A), causing arginine 506 to be replaced by glutamine at a site required for cleavage of FVa by activated protein C. Around 3-5% of the UK population shares this mutation. The tendency to venous thrombosis is increased by around 5-fold in FVL heterozygous subjects, and more so in the presence of other risk factors. Subjects homozygous for FVL are at much greater risk.

When coagulation is activated in the blood stream, protein C (PC) is converted to the anticoagulant activated protein C (APC) which destroys activated factor V (FVa) and activated factor VIII (FVIIIa), reducing risk of venous thromboembolism. A normal APCV test effectively rules out the presence of factor V Leiden in plasma.

Around 3-5% of the UK population shares a mutation in FV that reduces the anticoagulant effect of APC; this is factor V Leiden (FVL). FVL lacks a site required for destruction of factor FVa and the FVa persists in the blood longer than normal, increasing the tendency to venous thrombosis by around 5-fold if heterozygous, and more so in the presence of other risk factors. Subjects homozygous for FVL are at much greater risk. Rare patients with FVL have an allelic gene that does not function and the APCV test result suggests homozygous FVL and the patient has similar thrombotic risk as homozygous subjects.

Indications

Routinely carried out when the FVL screening test (APCV) result is abnormal or when we are unable to perform the APCV due to interfering factors or due to insufficient blood specimen being received. When genetic testing for FVL is specifically requested. Approximately 5% of the UK population is heterozygous for this polymorphism and guidelines recommend against family investigations of factor V Leiden in relatives.

Sample Type

Whole blood (Citrate Blue or EDTA Purple) x 1

Reference Range

Absence or presence of mutation indicated on the report.

Turnaround Time

Within 2 weeks

Testing Frequency

Weekly.

External Notes

Results FVL absent (normal) or abnormal due to presence of mutation (heterozygous or homozygous) indicated on the report. It is recommended that if the result is FVL homozygous, the test should be checked on a second occasion.

Patient Preparation

No special requirements.

References

Cooper et al, Evaluation of the Roche LightCycler: a simple and rapid method for direct detection of factor V Leiden and prothrombin G20210A genotypes from blood samples without the need for DNA extraction. Blood Coagul Fibrinolysis. 2003 Jul;14(5):499-503.
Baglin et al; British Committee for Standards in Haematology. Clinical guidelines for testing for heritable thrombophilia. Br J Haematol. 2010 Apr;149(2):209-220

Your contact for this test

Kieron Hickey

Thrombophilia Section Lead and Deputy Laboratory Manager - Coagulation

You are enquiring about

Factor V Leiden (FVL)