Also Known As
Activated Protein C Resistance
APC Resistance
Factor V R506Q
PT G20210A
Factor II 20210
Factor II Mutation
Formal Name
Factor V Leiden Mutation; Prothrombin 20210 Mutation
This article was last reviewed on
This article waslast modified on February 6, 2019.
At a Glance
Why Get Tested?

To determine whether you have an inherited gene mutation that increases your risk of developing a blood clot, including a deep venous thrombosis (DVT) and/or venous thromboembolism (VTE)

When To Get Tested?

When you have had an unexplained blood clot (thrombotic episode), especially when you are less than 50 years old, have recurrent DVT or VTE episodes, experienced DVT or VTE during pregnancy, had DVT at unusual sites, or have a strong family history of thrombosis

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None

You may be able to find your test results on your laboratory's website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab's website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab's website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called "normal" values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."

For more information, please read the article Reference Ranges and What They Mean.

What is being tested?

Factor V Leiden and prothrombin 20210 (PT 20210 or Factor II mutation) are genetic mutations that are associated with an increased risk of developing inappropriate blood clots. These mutations are tested by two separate tests that evaluate a person's DNA to look for the mutations. The two tests are often performed together to help determine if an individual has an inherited risk for excessive clotting.

Factor V and prothrombin are coagulation factors (sometimes called clotting factors), two of a group of proteins essential for proper blood clot formation. When an injury occurs and bleeding starts, a process called hemostasis begins to form a plug at the injury site to help stop the bleeding. Blood cells called platelets adhere to and aggregate at the injury site, and a coagulation cascade begins to activate coagulation factors in sequence. Eventually, a blood clot forms. Once the area has healed, the blood clot dissolves.

There must be an adequate number of each of the coagulation factors, and each must function normally in order for a stable blood clot to form and then dissolve when no longer needed. A deficiency in clotting factors (quantitative defect) or clotting factors that do not work properly (qualitative defect) can lead to excessive bleeding or clotting (thrombosis).

Factor V Leiden and PT 20210 are two mutations that individuals may inherit from their parents that may cause an increased risk of excessive clotting. They are inherited in an autosomal dominant manner. A person may inherit one mutated gene copy and be heterozygous or may inherit two mutated gene copies and be homozygous. This may determine to what extent the person is affected. (For additional details, read the section on Autosomal Dominant Inheritance in the Genetic Disorders article.)

These two mutations are independent and are tested separately, but the tests are often performed at the same time as part of the investigation of a blood clot (thrombotic episode) in someone who is suspected of having an inherited risk factor for an excessive clotting (hypercoagulable) disorder. Each test is used to identify whether or not the specific mutation is present and to determine whether the person has one copy (heterozygous) or two copies (homozygous) of that mutation.

  • During blood clotting, factor V is normally inactivated by a protein called activated protein C (APC) to prevent the blood clot from growing too large. But a factor V Leiden genetic mutation can lead to an altered factor V protein that resists inactivation by APC. The result is that clotting remains more active than usual, increasing risks of a blood clot forming in the deep veins of legs (DVT) or breaking off and blocking a vein (venous thromboembolism or VTE).
  • During blood clotting, an enzyme converts prothrombin to form thrombin. A mutation in the gene that codes for prothrombin called prothrombin 20210 can lead to increased amount of prothrombin and therefore abnormal clotting and an increased risk of a DVT or VTE.
Accordion Title
Common Questions
  • How is the test used?

    Factor V Leiden (FVL) mutation and prothrombin 20210 (PT 20210) mutation tests are two tests often used together to help diagnose the cause of inappropriate blood clot (thrombus) formation, including deep vein thrombosis (DVT) and/or venous thromboembolism (VTE).

    Testing for factor V Leiden and PT 20120 mutations is used to help determine if an individual has inherited a disorder associated with blood clots and can determine whether the person has one copy or two copies of the mutation (heterozygous or homozygous.)

    These tests may be ordered to help determine the reason for an initial harmful blood clot (thrombotic episode), especially when it occurs in a person under 50 years old, is unprovoked, or is in an unusual place such as the liver (hepatic), the kidneys (renal), the brain (cerebral), the gut and pelvis (mesenteric), or in the eye veins. These tests may also be ordered if VTE is recurrent or there is a strong family history of thrombosis.

    Experts do not recommend screening the general population and are divided on testing family members of those with a factor V Leiden or PT 20210 mutation. If the mutation is present, then the person is at a higher risk for developing a blood clot, but there is variability in how the gene is actually expressed. With factor V Leiden, for example, only 10% of those with the factor V Leiden mutation will ever have a thrombotic episode.

  • When is it ordered?

    Factor V Leiden mutation and PT 20210 tests are ordered when it is suspected that a person has an inherited risk factor for blood clots, for example, when an individual:

    • Has a first deep venous thrombosis (DVT) or venous thromboembolism (VTE) before age 50
    • Has recurring DVT or PE
    • Has a blood clot in an unusual part of the body such as the veins of the liver (hepatic), the kidneys (renal), the brain (cerebral), the gut and pelvis (mesenteric), or in the eye veins
    • Has a personal or family history of recurrent DVT or VTE
    • Has a first VTE related to oral contraceptive use, pregnancy or hormone replacement therapy 
    • Experiences unexplained miscarriages, especially those occurring in the second or third trimester of pregnancy

    These tests may be ordered when a first-degree family member, such as parent or sibling, has a factor V Leiden or PT 20210 gene mutation. However, a panel assembled by the Centers for Disease Control and Prevention to evaluate practical genomics recommended in 2011 that if the goal is to decide on treatment with anticoagulant medication, adults without VTE symptoms do not need to be tested even if their family members have the PT 20210 or the factor V Leiden mutation.

    If asymptomatic family members know that they have one or more of the mutations, they may be motivated to address controllable clotting risk factors such as oral contraceptive use, smoking, and elevated levels of homocysteine and be more aware of the potential risks of factor(s) triggering events, such as immobilization and surgery. However, many of those with the mutation will never experience a DVT or VTE.

  • What does the test result mean?

    If genetic testing indicates that an individual has one factor V Leiden or PT 20210 gene copy, then the person is heterozygous; if there are two copies, then the person is homozygous for the mutation.

    • Factor V Leiden mutation is the most common inherited predisposition to excessive clotting in the United States and it is most common in the Caucasian population. Between 3 and 8% of U.S. Caucasians carry one copy of the factor V Leiden mutation and about 1 in 5,000 people have two copies of the mutation. While homozygous cases of factor V Leiden are more rare, they also carry a higher risk of thrombosis. People with two copies of the mutation may have up to 80 times the risk of thrombophilia while those with one copy have 4 to 8 times the risk, compared to those who do not carry the mutation. 
    • Someone with a PT 20210 mutation may be heterozygous or homozygous, although it is very rare to find individuals who are homozygous. The affected heterozygous person will have a mild to moderate increase in their thrombin production, which is associated with 2.5 to 3 fold greater risk of developing a venous thromboembolism (VTE) in Caucasians; there is not enough information about risk in those who are homozygous. Although PT 20210 is less common in the U.S. than factor V Leiden, about 2 to 4% of Caucasians, usually of European ancestry, have a variation in the prothrombin gene. In the U.S., approximately 1 in 250 African Americans have the mutation.

    The risk of excessive clotting from these mutation(s) varies from person to person. If you are asymptomatic, you may never have a DVT and/or VTE. If you have had one or more blood clots, then the mutation(s) is the most likely cause and you have an increased risk for another clot. If no mutations are found, then it is likely that the condition is due to another cause.

    The risks that are associated with factor V Leiden, PT 20210, and other inherited and acquired factor deficiencies are independent. A person can have more than one risk factors for harmful blood clots, and their associated risks are cumulative. Added to inherited risks and acquired risks are controllable risk factors, such as use of oral contraceptives and hormone replacement therapy (HRT), that may worsen the combined underlying risk factors. For instance, if a woman has one gene copy with the factor V Leiden variant, she may be at about a 2 to 4 fold greater risk of developing a VTE. If she also uses oral contraceptives, the combined risk can increase to 35 times the risk for factor V Leiden heterozygosity alone, and women with factor V Leiden who take HRT have a 15-fold higher risk.

  • Is there anything else I should know?

    Sometimes, evaluation for the presence of a factor V Leiden mutation can begin with a test for activated protein C (APC) resistance, though it is not commonly performed nowadays. About 90% of the time, APC resistance is due to a factor V Leiden mutation, and the APC resistance ratio assay has a greater than 99% sensitivity for detecting a factor V Leiden mutation. If resistance is present, then a test for the factor V Leiden gene mutation is performed on the person's DNA, both to confirm the diagnosis and to determine whether the person has one or two copies of the mutation (is heterozygous or homozygous for the mutation).

    Some studies have found a significant association between factor V Leiden mutation and recurrent miscarriages.

  • In addition to factor V Leiden and PT 2010, what other tests might be done to evaluate excessive clotting?

    Several other tests may be used to help identify additional factors that may be contributing to excessive clotting (thrombophilia). Some of these include:

  • How are deep vein thrombosis (DVT) and/or venous thromboembolism (VTE) treated?

    Regardless of the underlying cause, a VTE is usually treated with a short course of anticoagulants, often 3 to 12 months. A combination of heparin, warfarin, and low-molecular weight heparins or one of the newer oral anticoagulants may be prescribed. At the end of this time period, the person's risk level is reassessed to see if further treatment is necessary. Lifetime prophylactic treatment may be needed for some patients.

  • Should someone with a factor V Leiden mutation be on long-term anticoagulant therapy?

    In general, no. Anticoagulant therapy is used when there is DVT and/or VTE. Long-term therapy may be considered for specific individuals, dependent upon the clinical situation. It should be noted that knowing whether a person with DVT/VTE has a factor V Leiden or prothrombin 20210 mutation does not change the intensity or duration of anticoagulant therapy.

  • Will factor V Leiden or PT 20210 ever go away?

    No. If you have one of these mutations, they are part of your genetic make-up and they will not go away. However, there are things you can do to lower your risk of developing a blood clot, such as not smoking.

  • What is the clinical relevance of factor V R2 mutation?

    R2 (A4070G) is a mild factor V mutation believed to confer additional APC resistance when it is present in individuals who are heterozygous for FVL (R506Q). By itself, the R2 mutation is not known to significantly contribute to venous thrombosis risk.

View Sources

Sources Used in Current Review

Learning About Factor V Leiden Thrombophila. National Human Genome Research Institute. Available online at https://www.genome.gov/15015167/learning-about-factor-v-leiden-thrombophilia. Accessed on 9/15/18.

Prothrombin G20210A (Factor II Mutation) Resources. National Blood Clot Alliance. Available online at https://www.stoptheclot.org/learn_more/prothrombin-g20210a-factor-ii-mutation. Accessed on 9/15/18.

(February 10, 2016) Considerations for Long-Term Anticoagulant Therapy in Patients with Venous Thromboembolism in the Novel Oral Anticoagulant Era. Vascular Health and Risk Management. Available online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4754098/. Accessed on 9/15/18.

Activated Protein C Resistance V (APCRV), Plasma. Mayo Medical Laboratories. Available online at https://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/81967. Accessed on 9/15/18.

(March 2015) Factor V Leiden Mutation in Women with Early Recurrent Pregnancy Loss: A Meta-Analysis and Systematic Review of the Causal Association. Archives of Gynecology and Obstetrics. Available online at https://link.springer.com/article/10.1007/s00404-014-3443-x. Accessed on 9/15/18.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

Coagulation Test Panels. Florida Hospital Cancer Institute, Clinical and Research Laboratories [Online information]. Available online at http://www.fhci-labs.com/researchlabs/clinicallabs/hemostasisandthrombosis/panels.htm.

Confusing Coagulation Test Names. UAB Coagulation Service, Univ of Alabama at Birmingham [Online information]. Available online at http://peir.path.uab.edu/coag/article_187.shtml.

Check, W. (1999 September). Labs Home In On Mutant Alleles. CAP Today, In the News [On-line Journal]. Available online at http://www.cap.org/captoday/archive/1999/cov999.html.

Chapter 132 Thrombotic Disorders, General. The Merck Manual of Diagnosis and Therapy, Section 11. Hematology And Oncology [Online information]. Available online at http://www.merck.com/pubs/mmanual/section11/chapter132/132a.htm.

Laposata, M. & Vancott, E. (2000 January). How to work up hypercoagulability. CAP Today, In the News [On-line Coagulation Case Study]. Available online at http://www.cap.org/CAPToday/casestudy/coag5.html.

Factor V Leiden. University of Illinois - Urbana/Champaign, Carle Cancer Center, Hematology Resource Page, Patient Resources [On-line information]. Available online at http://www-admin.med.uiuc.edu/hematology/PtFacV2.htm.

Ronald C. McGlennen, R. and Key, N. Clinical and Laboratory Management of the Prothrombin G20210A Mutation. College of American Pathologists, Practicing Pathology. Available online through http://www.cap.org.

Prothrombin Gene Mutation 20210A [11 paragraphs]. University of Illinois - Urbana/Champaign, Carle Cancer Center, Hematology Resource Page, Patient Resources [On-line information]. Available online at http://www-admin.med.uiuc.edu/hematology/PtProthrombin.htm.

Press, R. et. al. (2002). Clinical Utility of Factor V Leiden (R506Q) Testing for the Diagnosis and Management of Thromboembolic Disorders. Arch Pathol Lab Med 126: 1304-1318 [Online pdf of journal article]. PDF available for download at http://www.access-genetics.com/Arch_Pathol_Lab_Med_Vol%20126_Nov_2002_3.pdf.

(2001 January 10, Modified). Coagulation Test Descriptions, Factor V Leiden (Activated Protein C Resistance Pcr Assay) and Prothrombin (G20210A) Gene Polymorphism (PTG G20210A). Clinical Coagulation Laboratory, A division of Duke University Regional Referral Laboratory Services [Online information]. Available online at http://pathology.mc.duke.edu/coag/TestDes.htm.

Menta, S. (1999 Spring). The Coagulation Cascade. Physiology Disorders Evaluation, College of Medicine, Univ of Florida [On-line information]. Available online at http://www.medinfo.ufl.edu/year2/coag/title.html.

Bauer, K. (2001). The Thrombophilias: Well-Defined Risk Factors with Uncertain Therapeutic Implications. Ann Intern Med. 2001;135:367-373 [Journal]. Available online through http://www.annals.org.

DeLoughery, T. (1999 March 15). Tests of Hemostasis and Thrombosis. OHSU [Online student handout]. Available online at http://www.ohsu.edu/som-hemonc/handouts/deloughery/printtest.html.

Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 430-431.

Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry. AACC Press, Washington, DC. Harris, N. et. al. Chapter 19: Assessment of Hemostasis in the Clinical Laboratory, Pp 227-239.

Kujovich, J. (2007 February 12, Update). Factor V Leiden Thrombophilia. GENEReviews [On-line information]. Available online at http://www.genetests.org/query?dz=factor-v-leiden. Accessed on 3/14/07 .

Kujovich, J. (2006 July 25). Prothrombin Thrombophilia. GENEReviews [On-line information]. Available online through http://www.genetests.org. Accessed on 3/16/07.

Ornstein, D. and Cushman, M. (2003). Factor V Leiden. Circulation 2003:107;94-97 [On-line information]. PDF available for download at http://circ.ahajournals.org/cgi/reprint/107/15/e94.pdf. Accessed on 3/14/07.

University of Illinois Urbana/Champaign, Carle Cancer Center. Patient information on Factor V Leiden. Available online at http://www-admin.med.uiuc.edu/hematology/PtFacV2.htm. Accessed on June 2007.

McPherson R, Pincus M, eds, (2007) Henry's Clinical Diagnosis and Management by Laboratory Methods, 21st edition, Saunders Elsevier.

(Reviewed 2010 August). Factor V Leiden Thrombophilia. Genetics Home Reference [On-line information]. Available online at http://ghr.nlm.nih.gov/condition/factor-v-leiden-thrombophilia. Accessed September 2010.

Shah, S. and Voora, D. (Updated 2010 February 7). Genetics of Venous Thromboembolism. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/1797779-overview. Accessed September 2010.

Hart, K. et. al. (Updated 2010 August). Hypercoagulable States – Thrombophilia. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/Thrombophilia.html?client_ID=LTD. Accessed September 2010.

(2009 July). The Thrombophilias and Pregnancy. March of Dimes [On-line information]. Available online at http://www.marchofdimes.com/professionals/14332_9264.asp. Accessed September 2010.

Spence, R. et. al. (Updated 2010 January 12). Hemostatic Disorders, Nonplatelet eMedicine. [On-line information]. Available online at http://emedicine.medscape.com/article/210467-overview. Accessed September 2010.

Pagana, K. D. & Pagana, T. J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 430-431.

Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 48-49.

Centers for Disease Control and Prevention. Public Health Genomics, HUGENet Case study. Available online at http://www.cdc.gov/genomics/hugenet/CaseStudy/FVL/FVLview.htm. Accessed January 2011.

Netwellness.org. Bleeding and Clotting Disorders. The Genetics of Thrombosis. Available online at http://www.netwellness.org/healthtopics/clotting/genthromb.cfm. Accessed January 2011.

Mayo Clinic Staff. (2012 September 6). Factor V Leiden. Mayo Clinic. Available online at http://www.mayoclinic.org/diseases-conditions/factor-v-leiden/basics/definition/con-20032637. April 2014.

Reviewed by Hart, K. et al. (Reviewed 2010 August). Factor V Leiden Thrombophilia. Genetics Home Reference. Available online at http://ghr.nlm.nih.gov/condition/factor-v-leiden-thrombophilia. Accessed April 2014.

Shah, S. et al. (Updated August 31, 2012). Genetics of Venous Thromboembolism. Medscape. Available online at http://emedicine.medscape.com/article/1797779-overview. Accessed April 2014.

Hart, K. et. al. (Updated 2014 February). Hypercoagulable States – Thrombophilia. ARUP Consult. Available online at http://www.arupconsult.com/Topics/Thrombophilia.html?client_ID=LTD. Accessed April 2014.

Schwartz, R. et al. (Updated 2013 September 27). Factor II. Medscape. Available online at http://emedicine.medscape.com/article/209742-overview. Accessed April 2014.

Pagana, K. D. & Pagana, T. J. (© 2012). Mosby's Diagnostic and Laboratory Test Reference 11th Edition: Mosby, Inc., Saint Louis, MO. Pp 421-422.

Berg, A. et al. Recommendations from the EGAPP Working Group: Routine testing for Factor V Leiden (R506Q) and prothrombin (20210G>A) mutations in adults with a history of idiopathic venous thromboembolism and their adult family members. Genetics in Medicine (2011) 13, 67–76; doi:10.1097/GIM.0b013e3181fbe46f. Available online at http://www.nature.com/gim/journal/v13/n1/full/gim9201111a.html. Accessed April 2014.

Patel, K. et al. (Updated 2014 April 15). Deep Venous Thrombosis. Medscape. Available online at http://emedicine.medscape.com/article/758140-overview. Accessed April 2014.

Ghosh, Amit. (© 2010). Mayo Clinic Internal Medicine Review. 9th edition: Oxford University Press, Pg. 394.

Ask a Laboratory Scientist

This form enables you to ask specific questions about lab tests. Your questions will be answered by a laboratory scientist as part of a voluntary service provided by one of our partners, American Society for Clinical Laboratory Science.

Disclaimer
Thank you for using the Consumer Information Response Service ("the Service") to inquire about the meaning of your lab test results.  The Service is provided free of charge by the American Society for Clinical Laboratory Science, which is one of many laboratory organizations that supports Lab Tests Online.
Please note that information provided through this free Service is not intended to be medical advice and should not be relied on as such. Although the laboratory provides the largest single source of objective, scientific data on patient status, it is only one part of a complex biological picture of health or disease. As professional clinical laboratory scientists, our goal is to assist you in understanding the purpose of laboratory tests and the general meaning of your laboratory results. It is important that you communicate with your physician so that together you can integrate the pertinent information, such as age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), to determine your health status. The information provided through this Service is not intended to substitute for such consultations with your physician nor specific medical advice to your health condition.
By submitting your question to this Service, you agree to waive, release, and hold harmless the American Society for Clinical Laboratory Science and its affiliates or their past or present officers, directors, employees, agents, and Service volunteers (collectively referred to as "ASCLS") and the American Association  for Clinical Chemistry and its affiliates or their past or present officers, directors, employees, agents, and Service volunteers (collectively referred to as "AACC") from any legal claims, rights, or causes of action you may have in connection with the responses provided to the questions that you submit to the Service.
AACC, ASCLS and its Service volunteers disclaim any liability arising out of your use of this Service or for any adverse outcome from your use of the information provided by this Service for any reason, including but not limited to any misunderstanding or misinterpretation of the information provided through this Service.