Genetic Testing for Warfarin Sensitivity

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» Description» Selected References
» Prior Approval» Policy History
» Policy
 

Medical Policy: 02.01.33 
Original Effective Date: October 2007 
Reviewed: September 2014 
Revised: September 2014 


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This Medical Policy document describes the status of medical technology at the time the document was developed. Since that time, new technology may have emerged or new medical literature may have been published. This Medical Policy will be reviewed regularly and be updated as scientific and medical literature becomes available.


Description: 

Genetic variants in CYP2C9 and VKORC1 genes result in individual differences in the ability to metabolize warfarin. It has been proposed that using information regarding an individual’s CYP2C9 and VKORC1 genotypes, as well as other characteristics, to determine a personalized starting dose, may reduce the time to a stable warfarin dose and avoid serious bleeding events.

 

Warfarin is indicated for the prevention and treatment of thromboembolic events in high risk individuals; warfarin dosing is a challenging process, due to the narrow therapeutic window, variable response to dosing, and serious bleeding events in 5% or more of patients. Patients are typically initiated on a starting dose of 2-5 mg and monitored frequently with dose adjustments until a stable International Normalized Ratio (INR) value between 2 and 3 is achieved. During this period of adjustment, a patient is at high risk for bleeding.

 

Stable or maintenance warfarin dose varies among individuals; factors influencing stable dose include body mass index, age, interacting drugs, and indication for therapy. In addition, genetic variants of cytochrome p 450 2C9 (CYP2C9) and vitamin K epoxide reductase subunit C1 (VKORC1) genes together account for a substantial proportion of inter-individual variability.

 

Warfarin is metabolized by CYP2C9; genetic variants result in enzymes with decreased activity, increased serum warfarin concentration at standard doses, and a higher risk of serious bleeding.

 

Using the results of CYP2C9 and VKORC1 genetic testing to predict a warfarin starting dose that approximates the individual patient's likely maintenance dose may benefit patients by decreasing the risk of serious bleeding events and the time to stable INR. Algorithms have also been developed that incorporate not only genetic variation but also other significant factors to predict the best starting dose.

 

Practice Guidelines and Position Statement:

 

American College of Medical Genetics Policy Statement

Pharmacogenetic Testing of CYP2C9 and VKORC1 Alleles for Warfarin

Warfarin (Coumadin) is a potent drug that when used judiciously and monitored closely, leads to substantial reductions in morbidity and mortality from thromboembolic events. However, even with careful monitoring, initiation of warfarin dosing is associated with highly variable responses between individuals and challenges achieving and maintaining levels within the narrow therapeutic range that can lead to adverse drug events. Variants of two genes, CYP2C9 and VKORC1, account for 30-50% of the variability in dosing of warfarin; thus, many believe that testing of these genes will aid in warfarin dosing recommendations.

 

 Evidence about this test is evolving rapidly, as is its translation into clinical practice. In an effort to address this situation, a multidisciplinary expert group was organized in November 2006 to evaluate the role of CYP2C9 and VKORC1 testing in altering warfarin-related therapeutic goals and reduction of adverse drug events. A recently completed Rapid- ACCE (Analytical, Clinical Validity, Clinical Utility, and Ethical, Legal, and Social Implications) Review commissioned to inform this work group was the foundation for this analysis. From this effort, specific recommendations for the appropriate use of CYP2C9 and VKORC1 testing were developed and are presented here.

 

 

The group determined that the analytical validity of these tests has been met, and there is strong evidence to support association between these genetic variants and therapeutic dose of warfarin. However, there is insufficient evidence, at this time, to recommend for or against routine CYP2C9 and VKORC1 testing in warfarin-naive patients. Prospective clinical trials are needed that provide direct evidence of the benefits, disadvantages, and costs associated with this testing in the setting of initial warfarin dosing.


The 9th Edition of the American College of Chest Physicians Evidence Based Clinical Practice Guidelines on Antithrombotic Therapy and Prevention of Thrombosis, published in 2012, states:  “ For patients initiating VKA (vitamin K antagonist) therapy, the expert panel recommends against the routine use of pharmacogenetic testing for guiding doses of VKA.”


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Prior Approval: 

 

Not applicable


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Policy: 

See also medical policy for CYP450 Genotyping to Determine Drug Metabolizer Status 02.04.48

 

Genetic testing to determine cytochrome p450 2C9 (CYP2C9) and vitamin K epoxide reductase subunit C1 (VKORC1) genetic polymorphisms is considered investigational for the purpose of managing the administration and dosing of warfarin, including use in guiding initial warfarin dose to decrease time to stable INR and reduce the risk of serious bleeding.

 

While the evidence suggests a strong association between genetic variants and stable warfarin dose, and to a lesser extent, between genetic variants and INR and bleeding outcomes, the evidence is not sufficient to conclude that testing for CYP2C9 and VKORC1 genetic variants improves health outcomes. Genetic testing may help predict the initial warfarin dose within first week of warfarin treatment, but the evidence does not support the conclusion that clinically relevant outcomes, such as bleeding rates or thromboembolism are improved. Therefore, genotyping for variants to predict initial warfarin dose is considered investigational.





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Procedure Codes and Billing Guidelines: 

  • To report provider services, use appropriate CPT* codes, Modifiers, Alpha Numeric (HCPCS level 2) codes, Revenue codes, and/or ICD-9-CM diagnostic codes.
  • G9143 Warfarin responsiveness testing by genetic technique using any method, any number of specimen(s)
  • 81227 CYP2C9 (cytochrome P450, family 2, subfamily C, polypeptide 9) (eg, drug metabolism), gene analysis, common variants (eg, *2, *3, *5, *6)
  • 81355 VKORC1 (vitamin K epoxide reductase complex, subunit 1) (eg, warfarin metabolism), gene analysis, common variants (eg, -1639/3673)

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Selected References: 

  • Wadelius M, Chen LY, Downes K et al. Common VKORC1 and GGCX polymorphism associated with warfarin dose. Pharmacogenomics J 2005; 5(4):262-70.
  • Sconce EA, Khan TI, Wynne HA et al. The impact of CYP2C9 and VKORC1 genetic polymorphism and patient characteristics upon warfarin dose requirements: proposal for a new dosing regimen. Blood. 2005; 106(7):2329-33.
  • McClain MR, Palomaki GE, Piper M et al. A rapid ACCE 1 review of CYP2C9 and VKORC1 allele testing to inform warfarin dosing in adults at elevated risk for thrombotic events to avoid serious bleeding.
  • Millican E, Lensini PA, Milligan PE et al. Genetic-based dosing in orthopaedic patients beginning warfarin therapy. Blood 2007; 110(5):1511-5.
  • Zhu Y, Shennan M, Reynolds KK et al. Estimation of warfarin maintenance dose based on VKORC1 (-1639 G>A) and CYP2C9 genotypes. Clin Chem 2007; 53(7):1199-205.
  • Gage BF, Eby C, Milligan PE et al. Use of pharmacogenetics and clinical factors to predict the maintenance dose of warfarin. Thromb Haemost 2004; 91(1):87-94.
  • Schwarz UI, Ritchie MD, Bradford Y et al. Genetic Determinants of Response to Warfarin during Initial Anticoagulation. N Engl J Med 2008; 358:999-1008.
  • The International Warfarin Pharmacogenetics Consortium. Estimation of the Warfarin Dose with Clinical and Pharmacogenetic Data. N Engl J Med 2009; 360:753-64.
  • Eckman MH, Rosand J, Greenberg SM et al. Cost-effectiveness of Using Pharmacogenetic Information in Warfarin Dosing for Patients with Nonvalvular Atrial Fibrillation. Ann Intern Med. 2009; 150:73-83.
  • Centers for Medicare and Medicaid Services. Decision Memo for Pharmacogenomic Testing for Warfarin Response (CAG-00400N). August 3, 2009.
  • Epstein RS, Moyer TP, Aubert RE et al. Warfarin Genotyping Reduces Hospitalization rates. Results from the MM-WES (Medco-Mayo Warfarin Effectiveness Study). J Am Coll Cardiol 2010; 55:2804-12.
  • Ferder NS, Eby CS, Deych E et al. Ability of VKORC1 and CYP2C9 to predict therapeutic warfarin dose during the initial weeks of therapy. J Thromb Haemost. 2010 Jan;8(1):95-100. Epub 2009 Oct 30.
  • McMillin GA, Melis R, Wilson A et al. Gene-based warfarin dosing compared with standard of care practices in an orthopedic surgery population: a prospective, parallel cohort study. Ther Drug Monit. 2010 Jun;32(3):338-45.
  • ECRI Institute. Plymouth Meeting (PA). April 2011. Emerging Technology Evidence Report. Pharmacogenetic testing to determine warfarin dose.
  • Lefferts JA, Schwab MC, Dandamudi UB et al. Warfarin genotyping using three different platforms. Am J Transl Res. 2010 Jul 25;2(4):441-6.
  • Anderson JL, Horne BD, Stevens SM et al. A randomized and clinical effectiveness trial comparing two pharmacogenetic algorithms and standard care for individualizing warfarin dosing (CoumaGen-II). Circulation. 2012 Apr 24; 125(16):1997-2005. Epub 2012 Mar 19. 
  • UpToDate. Overview of Pharmacogenomics. Kelan Tantisira, M.D., MPH, Scott T. Weiss, M.D., MS. January 18, 2013
  • ECRI InstituteWhy Isn't Pharmacogenetic Testing Widespread for Anticoagulant Dosing?  Published 9/1/2012. American College of Medical Genetics. ACMG Policy Statement: Pharmacogenetic Testing of CYP2C9 and VKORC1 Alleles for Warfarin. Issued 2008
  • American College of Medical Genetics. ACMG Policy Statement: Pharmacogenetic Testing of CYP2C9 and VKORC1 Alleles for Warfarin. Issued 2008
  •  Evidence-Based Management of Anticoagulation Therapy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence Based Clinical Practice Guidelines. Chest 1210 Feb;141(2 Suppl):e152S-84S.
  • American College of Obstetricians and Gynecologists (ACOG), Committee Opinion, Number 488 May 2011. Pharmacogenetics. 2011:117:1240-1.
  • Centers for Medicare and Medicaid Services. National Coverage Determination (NCD) for Pharmacogenomic Testing for Warfarin Response (90.1). www.cms.gov
  • Gary Stack, M.D., PhD, Pathology Consultation on Warfarin Pharmacogenetic Testing. Am J Clin Pathol 2011:135:13-19
  • UpToDate. Therapeutic use of Warfarin and Other Vitamin K Antagonists. Karen A. Valentine M.D.,PhD, Russell D. Hull, MBBS, MSc. Topic last updated August 5, 2014. www.uptodate.com
  • UpToDate. Overview of Pharmacogenomics. Kelan Tantisira, M.D., MPH, Scott T. Weiss, M.D., MS. Topic last updated July 29, 2014. www.uptodate.com
  • Pharmacological Reviews, Pharmacogenetics and Cardiovascular Disease-Implications for Personalized Medicine, Julie A. Johnson and Larisa H. Cavallari. Pharmacol Rev 65:987-1009 July 2013.
  • MedScape. Pharmacogenetics: From Discovery to Patient. www.medscape.com/viewarticle/590270  

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Policy History: 

 

 

Date                                         Reason                               Action

September 2010                      Annual review                     Policy renewed

November 2011                      Annual review                      Policy renewed

November 2012                      Annual review                      Policy renewed

October 2013                         Annual review                      Policy revised

September 2014                     Annual review                      Policy revised


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