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What is a Factor V Leiden test?
Factor V is a protein responsible for blood clot formation and prevention of excessive bleeding due to injuries. In the normal blood clotting mechanism, factor V is activated along with the activation of blood platelets and once clotting happens, it is usually inhibited by activated protein C, which prevents the formation of larger clots. However, if there is a gene mutation in this factor V, it develops resistance to activated protein C. As a result, the clotting process remains active and there is an increased risk of developing a blood clot in the deep leg veins (DVT). Occasionally, the clot may break off and cause blocking of a vein, i.e, venous thromboembolism (VTE).

A factor V Leiden test is a blood test that evaluates genetic mutations in factor V, a blood-clotting protein to prevent such conditions.

  1. Why is a Factor V Leiden test performed?
  2. How do you prepare for a Factor V Leiden test?
  3. How is a Factor V Leiden test performed?
  4. What do Factor V Leiden test results indicate?

A factor V Leiden test is performed if a person has a risk of inheriting factor V mutation or when someone has:

  • The first episode of DVT or VTE before the age of 50 years
  • Recurrent VTE or DVT episodes
  • Blood clot at an unusual site, such as the veins of kidneys, liver, pelvis or eyes
  • History or family history of recurrent VTE or DVT
  • First episode of VTE in women after the use of contraceptive pills or undergoing hormone replacement therapy or in pregnancy
  • Unexplained miscarriages occurring in the second or third trimester

A factor V Leiden test is also performed when symptoms of DVT are suspected, which include

  • Leg pain, tenderness in one leg (affected leg)
  • Extensive pain in the affected area
  • Swelling of the affected leg (oedema)
  • Warm skin in the area of the clot
  • Discolouration of the affected leg

Furthermore, this test is performed when a person shows symptoms of pulmonary embolism, which include

No special preparations are needed for this test.

An experienced laboratory specialist will collect a blood sample from a vein in your arm by inserting a small needle. A small quantity of blood will be withdrawn into a sterile vial or a test tube. A momentary pricking pain is felt when the needle goes in the vein.
There is a minimal risk of pain, light-headedness and bruising at the site of injection after the test. However, at most times, these symptoms disappear quickly. Rarely, an infection may occur at the injection site.

Normal results: Absence of factor V Leiden mutation indicates normal results, which means that there are lower chances of DVT and VTE or its recurrence. In addition, the absence of the mutation signifies that the cause of current DVT or VTE is not a factor V mutation, and the symptoms need further evaluation for a conclusive diagnosis.

Abnormal results: Positive results for factor V mutation can have a couple of inferences, ie, it can be either heterozygous (one gene normal, while the other one mutated) or homozygous (both the genes are mutated). An individual having heterozygous genes possesses mild to moderate risk of developing DVT or VTE, whereas patients with homozygous gene mutation are at very high risk of developing DVT or VTE.
Individuals with both mutated copies can have up to 80 times higher risk of thrombophilia, whereas those with only one of the mutated copies carry 4 to 8 times the risk compared to those who do not carry such mutations.
The risk of having a harmful blood clot increases if this mutation is coupled with other risk factors. For instance, if a woman has heterozygous factor V mutation, and she uses oral contraceptive pills, her combined risk for abnormal clot formation increases by 35 times. A factor V Leiden test is usually coupled with certain other tests, such as lupus anticoagulants, protein C and protein S, antithrombin and homocysteine levels, for identifying the cause of thrombophilia.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

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References

  1. Lab tests Online. [Internet] American Association of Clinical Chemistry, U.S. Factor V Leiden Mutation and PT 20210 Mutation
  2. National Health Service [Internet]. UK; Overview - Deep vein thrombosis
  3. University of Rochester Medical Center. [Internet] Rochester (NY): University of Rochester Medical Center; Factor V
  4. Deborah L. Ornstein, Mary Cushman. Factor V Leiden Circulation, April 2003, Vol: 107, No: 15
  5. Emmanuel J Favaloro, David McDonald. Futility of testing for factor V Leiden Blood Transfus. 2012 Jul; 10(3): 260–263 PMID: 22889816