Clopidogrel (CYP2C19 Genotyping)

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Also known as: Clopidogrel Pharmacogenetic Testing; CYP2C19 Genotype
Formal name: CYP2C19 Sequence Genotype

At a Glance

Why Get Tested?

To help evaluate the likely response of a person at risk of a heart attack or stroke to the antiplatelet drug clopidogrel, which helps to prevent harmful blood clots from forming, by detecting variations in the gene (the CYP2C19 gene) that codes for one of the enzymes that metabolizes the drug

When to Get Tested?

A doctor 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 in your arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

This test helps determine if a person may be less responsive to the drug clopidogrel because of his or her genetic makeup. This test detects genetic variation in the gene CYP2C19. A doctor may sometimes order this test to determine whether clopidogrel will be effective for the person tested 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.

Each person receives one copy of each of their genes from their mother and one copy of each of their genes from their father. Thus, the CYP2C19 gene is present in the body as two inherited gene copies (alleles). Any person could have both copies of a gene without any variants ("wild-type"); one copy without variants and one copy with a variant ("heterozygous"); both copies with the same variant ("homozygous"); and both copies with different variants ("compound heterozygous"). The combination of the CYP2C19 gene copies that a person has can determine how effectively clopidogrel is changed to its active form in the 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 doctor decide the appropriate antiplatelet treatment for the person tested.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

Common Questions

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Article Sources

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

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 through http://circ.ahajournals.org. 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 through http://www.nlm.nih.gov. 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 through http://www.aacc.org. 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 through http://www.arupconsult.com. 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 through http://www.mayomedicallaboratories.com. 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 through http://www.medscape.com. 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 through http://www.medscape.com. 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 through http://www.medscape.com. 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 through http://www.medscape.com. 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 through http://www.mc.vanderbilt.edu. 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 through http://www.medscape.com. 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 through http://www.medscape.com. 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.