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.
A blood sample drawn from a vein in your arm
Test Preparation Needed?
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.
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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.
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Linnea Baudhuin, Phd, DABMG. Assistant Professor of Laboratory Medicine. Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN.