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.
Clopidogrel (CYP2C19 Genotyping)
Clopidogrel (CYP2C19 Genotyping)
Also Known As
Clopidogrel Pharmacogenetic Testing
CYP2C19 Genotype
Formal Name
CYP2C19 Sequence Genotype
This article was last reviewed
on
This article waslast modified
on January 4, 2018.
At a Glance
Why Get Tested?
When To Get Tested?
A health 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 in your arm
Test Preparation Needed?
None
Accordion Title
Common Questions
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How is it used?
This test is used to determine an individual's potential responsiveness to clopidogrel, an antiplatelet medication, before a person starts taking the drug or during the initial treatment phase. Clopidogrel is a drug that is prescribed 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).
Clopidogrel genotype testing is used to detect variation in the CYP2C19 gene that codes for one of the enzymes responsible for metabolizing clopidogrel into its active form. Variation in CYP2C19 is most often associated with reduced enzyme activity and decreased metabolism of clopidogrel, leading to a low level of active drug and potentially ineffective treatment for risk of blood clots. Testing for variants of the CYP2C19 gene is done to help tailor treatment for an individual (known as pharmacogenetic testing). Those with certain genetic variations may require an alternative therapy that would treat their condition more effectively.
Clopidogrel-related genetic testing is not widely used at this time. Although studies have shown that CYP2C19 variation contributes to a person's responsiveness to clopidogrel, there is no agreement yet among experts on the need for the testing. Part of the reason is that genetic variants of CYP2C19 explain only a small proportion of the treatment response variability among people.
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When is it ordered?
Clopidogrel resistance testing is primarily ordered prior to a person taking clopidogrel for the first time or during the initial treatment phase but may also be ordered when a person who is being treated with the drug has experienced either excessive blood clotting or bleeding.
Not everyone who is prescribed clopidogrel will have this test done. At present, there is no consensus on the usefulness of this test and it is not yet widely accepted.
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What does the test result mean?
Results of genetic testing require careful interpretation. Typically, the lab report will include an explanation from a health practitioner with expertise in this area. A number of factors are taken into account when determining whether clopidogrel is an appropriate treatment for an individual.
In general, if a person has one or two variant copies of the gene, then that person may have an altered response to clopidogrel. The degree of responsiveness depends upon the variation(s) present and upon the person. An individual may be a normal, poor, intermediate, extensive, or ultra-rapid metabolizer of the drug.
Not every laboratory will test for every gene variant. A less common gene variant may be present that is not detected by the test. A person may also have decreased drug metabolism due to another factor. CYP2C19 gene variation only accounts for a portion of a person's response to clopidogrel.
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Is there anything else I should know?
To increase awareness of the influence of the CYP2C19 gene variations and the availability of testing, the U.S. Food and Drug Administration (FDA) has promoted changes to the Plavix® (clopidogrel) label to inform consumers that genetic factors may affect how well the drug works for them.
The enzyme CYP2C19, coded for by the CYP2C19 gene, metabolizes a wide variety of drugs in addition to clopidogrel. Thus, if a person is taking clopidogrel plus one or more additional medications metabolized by CYP2C19, then that person may have altered metabolism of clopidogrel and the other drugs. One of the prominent examples of drugs that are metabolized by CYP2C19 is omeprazole that is taken to control stomach acid production. Others include diazepam, anti-seizure medications, and antidepressants.
Testing to predict how someone will respond to a drug is a form of personalized medicine known as pharmacogenomics. It is a relatively new field of study developed in an effort to treat individuals' conditions effectively, yet avoid side effects.
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Is this test different than a platelet function test?
Yes. This test is a genetic test that determines which form of the CYP2C19 gene you have, which may help predict how you will respond to clopidogrel.
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Can platelet function assays be used to assess clopidogrel response?
There are several platelet function assays that have been used for detecting nonresponse (termed "clopidogrel resistance"), such as platelet aggregometry with ADP, with collagen epinephrine; however, their clinical utility has not been widely accepted due to poor agreement between the assays.
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Should everyone be tested for CYP2C19 gene variations?
Testing is not recommended to screen the general population. It is currently only indicated for those taking a drug that may be influenced by the activity of the CYP2C19-related enzymes. In some cases, a health practitioner may recommend that family members of a poor metabolizer consider testing so that this information is on record.
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Can clopidogrel resistance testing be done in my doctor's office?
No, it requires specialized equipment to perform and expertise to interpret. It is not offered by every laboratory and may need to be sent to a laboratory outside of your hospital (reference laboratory).
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Should I tell my other healthcare providers about my CYP2C19 test results?
Yes, this would be good information for them to have, regardless of whether you are currently taking clopidogrel.
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Should I tell my healthcare providers that I am taking clopidogrel?
Yes, it is crucial for you to tell all of your healthcare providers and your dentist that you are taking clopidogrel, aspirin, or another antiplatelet agent. They will need to incorporate this information into any other treatments or procedures.
