Factor V Leiden With Reflex to R2

CPT: 81241
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Test Details

Test Includes

Factor V Leiden; reflex to factor V R2 on positives


Detection of the factor V Leiden mutation, followed by testing for the factor V R2 polymorphism in individuals found to be positive for factor V Leiden (heterozygous). These tests provide information about increased risk for venous thrombosis, which can be helpful for prevention and for genetic counseling regarding risk to relatives. The factor V R2 polymorphism does not occur in individuals who are factor V Leiden homozygotes.


See individual tests.

Additional Information

The factor V Leiden mutation causes activated protein C (APC) resistance and increases the risk for venous thrombosis and pulmonary embolism. Heterozygotes (with one copy of the mutation) have a sevenfold increased risk, and homozygotes (with two copies) have a 50% to 80% increased risk. These risks are elevated further by additional genetic defects in naturally occurring anticoagulant proteins (eg, deficiencies of protein C, protein S, or antithrombin) and by situations that tend to provoke thrombosis (eg, major surgery, oral contraceptive use, pregnancy, malignancy, immobility). Factor V Leiden is also associated with increased risk for multiple pregnancy loss. Factor V Leiden is present in 5% to 7% of the general population and 20% to 40% of individuals with venous thrombosis.

The factor V R2 polymorphism is associated with decreased levels of factor V and it significantly increases risk of venous thrombosis in individuals who are heterozygous for the factor V Leiden mutation. Coexistence of the R2 polymorphism with factor V Leiden increases the risk for venous thrombosis approximately to a 16-fold increased risk. The average age of the first thrombotic event is six years younger in individuals who are heterozygous for both factor V Leiden and the R2 polymorphism than in those with factor V Leiden alone. The R2 polymorphism is common in the general population, with one copy (heterozygous) in 10% of individuals. Among patients with venous thrombosis, approximately 12% are heterozygous for the R2 polymorphism. Indications for testing: Venous thrombosis, pulmonary embolism, peripheral vascular disease (particularly lower extremity occlusive disease), premature stroke or transient ischemic attack, myocardial infarction in female smokers under age 50, women with multiple pregnancy loss. Also, family history of venous thrombosis or a relative known to have the factor V Leiden mutation. Factor V R2 DNA analysis will automatically be performed on the same sample for individuals found to be heterozygous for the factor V Leiden mutation.

Specimen Requirements


Whole blood


5 mL

Minimum Volume

0.5 mL (Note: This volume does not allow for repeat testing.)


Lavender-top (EDTA) tube (preferred) or yellow-top (ACD) tube

Storage Instructions

Maintain specimen at room temperature or refrigerate. Stable at room temperature for eight days.

Causes for Rejection

Clotted whole blood samples if adequate DNA not obtained; incorrect specimen type; frozen whole blood specimens

Clinical Information


Alhenc-Gelas M, Nicaud V, Gandrille S, et al. The factor V gene A4070G mutation and the risk of venous thrombosis. Thromb Haemost.1999 Feb; 81(2):193-197.10063990
Castoldi E, Brugge JM, Nicolaes GA, Girelli D, Tans G, Rosing J. Impaired APC cofactor activity of factor V plays a major role in the APC resistance associated with the factor V Leiden (R506Q) and R2 (H1299R) mutations. Blood. 2004 Jun 1; 103(11):4173-4179. 14976057
Dahlbäck B. Advances in understanding pathogenic mechanisms of thrombophilic disorders. Blood. 2008 Jul 1;112(1):19-27. 18574041
Faioni EM, Franchi F, Bucciarelli P, et al. Coinheritance of the HR2 haplotype in the factor V gene confers an increased risk of venous thromboembolism to carriers of factor V R506Q (factor V Leiden). Blood. 1999 Nov 1; 94(9):3062-3066. 10556190
Folsom A, Cushman M, Tsai MY, et al. A prospective study of venous thromboembolism in relation to factor V Leiden and related factors. Blood. 2002 Apr 15; 99(8):2720-2725.
Grody WW, Griffin JH, Taylor AK, Korf BR, Heit JA; American College of Medical Genetics consensus statement on factor V Leiden mutation testing. Genet Med. 2001 mAR-aPR; 3(2):139-148. 11280951
Hoekema l, Castoldi E, Tans G, et al. Functional properties of factor V and factor Va encoded by the R2-gene. Thromb Haemost. 2001 Jan; 85(1):75-81. 11204592
Rosendaal FR, Koster T, Vandenbroucke JP, Reitsma PH. High risk of thrombosis in patients homozygous for factor V Leiden (activated protein C resistance). Blood. 1995 Mar 15, 85(6):1504-1508. 7888671

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