Clopidogrel (CYP2C19 Genotyping)
- Also Known As:
- Clopidogrel Pharmacogenetic Testing
- CYP2C19 Genotype
- Formal Name:
- CYP2C19 Sequence Genotype

This page was fact checked by our expert Medical Review Board for accuracy and objectivity. Read more about our editorial policy and review process.
At a Glance
Why Get Tested?
To help evaluate your likely response to the antiplatelet drug clopidogrel by detecting variations in the gene (CYP2C19) that codes for one of the enzymes that metabolizes the drug; clopidogrel is prescribed for people who are at risk of a heart attack or stroke to help prevent harmful blood clots from forming.
When To Get Tested?
A health care practitioner might order this test prior to prescribing clopidogrel for you or during the initial treatment phase and sometimes when you are taking clopidogrel and are not responding as expected.
Sample Required?
A blood sample drawn from a vein, a swab rubbed on the inside of your cheek, or you spit saliva in a clean container.
Test Preparation Needed?
None
What is being tested?
This test helps determine if you may be less responsive to the drug clopidogrel because of your genetic makeup. This test detects genetic variation in the gene CYP2C19. A health care practitioner may sometimes order this test to determine whether clopidogrel will be effective for you or if another drug for treatment may be required.
Clopidogrel is a drug that is part of a group of medications called antiplatelet drugs and is used to prevent strokes and heart attacks in people who are at increased risk for these serious cardiovascular events. The drug works by helping to prevent harmful blood clots from forming by preventing platelets from clumping together (aggregating).
Normally, when an injury occurs to blood vessels, platelets in the blood stick to the site of injury and clump together to start the formation of a blood clot and help stop the bleeding. In people at increased risk for heart attack or stroke, this process can occur inappropriately, so they may be treated with drugs that prevent platelet aggregation.
Clopidogrel is given in an inactive form (i.e., prodrug) and must be changed (metabolized) by the body to an active form before it can be effective. Some people who have some genetic variations in the gene CYP2C19 do not metabolize clopidogrel to its active form as well as people who do not have these genetic variations in CYP2C19. Therefore, individuals with CYP2C19 genetic variations who are taking clopidogrel may not receive adequate benefit from the drug and may be at risk of having a heart attack or stroke. This test identifies people who have one or more CYP2C19 variants.
You inherit one copy of each of your genes from your mother and one copy from your father. Thus, the CYP2C19 gene is present in the body as two inherited gene copies (alleles). You could have both copies of a gene without any variants (wild-type, normal); one copy without variants and one copy with a variant (heterozygous); both copies with the same variant (homozygous); or both copies with different variants (compound heterozygous). The combination of the CYP2C19 gene copies that you have can determine how effectively clopidogrel is changed to its active form in your body and its overall effect.
Clopidogrel responsiveness (or clopidogrel genotype) testing determines whether CYP2C19 gene variants are present. Careful interpretation of the results can help the healthcare provider decide the appropriate antiplatelet treatment for you.
Common Questions
View Sources
Sources Used in Current Review
Davenport, L. (2019 September 3). Genetic Testing Spots Clopidogrel Responders After PCI for STEMI. Medscape Conference News, ESC 2019. Available online at https://www.medscape.com/viewarticle/917639. Accessed July 2020.
(2015 December, Reviewed) CYP2C19 gene. Genetics Home Reference. Available online at https://ghr.nlm.nih.gov/gene/CYP2C19. Accessed July 2020.
McMillin, G. Medical Expert (2019 October, Updated). Germline Pharmacogenetics – PGx. ARUP Consult. Available online at https://arupconsult.com/content/germline-pharmacogenetics?_ga=2.234289693.2056076676.1573304696-1793245273.1560683717. Accessed July 2020.
Tanaka, T. et. al. (2019 June). Association of CYP2C19 Polymorphisms With Clopidogrel Reactivity and Clinical Outcomes in Chronic Ischemic Stroke. Circ J 2019; 83: 1385–1393. Available online at https://www.jstage.jst.go.jp/article/circj/83/6/83_CJ-18-1386/_article. Accessed July 2020.
(© 1998-2020). CYP2C19/Clopidogrel Pharmacogenomic Lab Test. Mayo Clinic Centers and Programs, Center for Individualized Medicine. Available online at https://www.mayo.edu/research/centers-programs/center-individualized-medicine/patient-care/pharmacogenomics/drug-gene-testing/cyp2c19-clopidogrel. Accessed July 2020.
(2015 December, Reviewed). Clopidogrel resistance. Genetics Home Reference. Available online at https://ghr.nlm.nih.gov/condition/clopidogrel-resistance. Accessed July 2020.
Hughes, S. (2018 March 12). New Studies Encourage Clopidogrel Genotyping. Medscape Conference News ACC 2018. Available online at https://www.medscape.com/viewarticle/893764. Accessed July 2020.
(2017 August 3, Current). FDA Drug Safety Communication: Reduced effectiveness of Plavix (clopidogrel) in patients who are poor metabolizers of the drug. US Food & Drug Administration. Available online at https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/fda-drug-safety-communication-reduced-effectiveness-plavix-clopidogrel-patients-who-are-poor. Accessed July 2020.
Chong, K. (2015 October 22, Updated). Clopidogrel Dosing and CYP2C19. Medscape Genomic Medicine. Available online at https://emedicine.medscape.com/article/1733280-overview. Accessed July 2020.
Dean, L. (2018 April 18, Updated). Clopidogrel Therapy and CYP2C19 Genotype. Medical Genetics Summaries [Internet]. Available online at https://www.ncbi.nlm.nih.gov/books/NBK84114/. Accessed July 2020.
Sources Used in Previous Reviews
Holmes, D et al. (2010 June 28). ACCF/AHA Clopidogrel Clinical Alert: Approaches to the FDA “Boxed Warning” A Report of the American College of Cardiology Foundation Task Force on Clinical Expert Consensus Documents and the American Heart Association. Circulation. 2010; 122: 537-557 [On-line information]. PDF available for download at http://circ.ahajournals.org/content/122/5/537.full.pdf. Accessed July 2011.
(Reviewed 2010 November 1). Clopidogrel. MedlinePlus Drug Information [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/druginfo/meds/a601040.html. Accessed July 2011.
Malone, Bill (2009 March 26). Predicting Response to Clopidogrel New Evidence Links Genes with Outcomes. Clinical Laboratory Strategies [On-line information]. Available online at http://www.aacc.org/publications/strategies/archives/2009/Pages/032609.aspx. Accessed July 2011.
McMillin, G et al. (Updated 2010 August). Pharmacogenetics – PGx. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/PGx.html. Accessed July 2011.
(© 1995-2011). Unit Code 60439: Cytochrome P450 2C19 Genotype by Sequence Analysis Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/60439. Accessed July 2011.
Hughes, S. (2010 October 21). Vanderbilt Now Also Routinely Gene Testing for Clopidogrel Metabolizer Status. Medscape Today from Heartwire [On-line information]. Available online at http://www.medscape.com/viewarticle/731001. Accessed July 2011.
Momary, K. et. al. (2010 April 13). Genetic Causes of Clopidogrel Nonresponsiveness: Which Ones Really Count? Medscape Today from Pharmacotherapy. 2010;30(3):265-274 [On-line information]. Available online at http://www.medscape.com/viewarticle/719480. Accessed July 2011.
Nainggolan, L. (2010 December 21). Newly Identified Variants Are Major Predictors of Response to Clopidogrel. Medscape Today from Heartwire [On-line information]. Available online at http://www.medscape.com/viewarticle/734643. Accessed July 2011.
Hughes, S. (2011 May 5). New Study Refutes Role of PON1 Gene in Clopidogrel Treatment. Medscape Today from Heartwire [On-line information]. Available online at http://www.medscape.com/viewarticle/742206. Accessed July 2011.
Snyder, B. (2010 September 23). Patient genotypes guide drug therapy in new VU program. Reporter, Vanderbilt University Medical Center’s Weekly Newspaper [On-line information]. Available online at http://www.mc.vanderbilt.edu/reporter/index.html?ID=9466. Accessed July 2011.
Hughes, S. (2010 July 22). Therapeutic Window Identified for Clopidogrel? Medscape Today from Heartwire [On-line information]. Available online at http://www.medscape.com/viewarticle/725625. Accessed July 2011.
Voora, D. and Shah, S. (2009 December 7). Defining the Link Between CYP2C19*2 and Clopidogrel Response. Medscape Today Viewpoints in Genomic Medicine [On-line information]. Available online at http://www.medscape.com/viewarticle/713197. Accessed July 2011.
Pagana, K. D. & Pagana, T. J. (© 2011). Mosby’s Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 368-369.
Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 1713-1717.
Linnea Baudhuin, Phd, DABMG. Assistant Professor of Laboratory Medicine. Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN.
Michael J. Knauer, Moderator, Eleftherios P. Diamandis, Moderator, Jean-Sebastien Hulot, Expert, Richard B. Kim, Expert and Derek Y.F. So, Expert. Clopidogrel and CYP2C19: Pharmacogenetic Testing Ready for Clinical Prime Time? Clinical Chemistry October 2015 vol. 61 no. 10 1235-1240. Available online at http://www.clinchem.org/content/61/10/1235.full. Accessed October 2015.
Gennaro Sardella, MD; Simone Calcagno, MD. The Importance of Genotype Variation Beyond Different Antiplatelet Therapy in Nonresponder Patients. J Am Coll Cardiol. 2014;64(3):333-334.
Bhopalwala A, et al. Routine Screening for CYP2C19 Polymorphisms for Patients being Treated with Clopidogrel is not Recommended. Hawaii J Med Public Health. 2015 Jan; 74(1): 16–20. Available online at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4300541/. Accessed October 2015.
Levine G, et al. Expert consensus document: World Heart Federation expert consensus statement on antiplatelet therapy in East Asian patients with ACS or undergoing PCI. Nature Reviews Cardiology 11, 597–606 (2014). Available online at http://www.nature.com/nrcardio/journal/v11/n10/full/nrcardio.2014.104.html. Accessed October 2015.
Ask a Laboratory Scientist
