What is pharmacogenetic testing?

Pharmacogenetics (also called pharmacogenomics) is the study of how your genes affect the way your body responds to certain medicines. Your genes are passed down from your parents. They carry information (called DNA) that determines many things about you, such as your height and eye color.

Some genes also affect how your body uses and breaks down medicines. Differences in these genes can be the reason why some people may benefit from a certain medicine while others may not benefit at all. Genes can also be the reason why some people have serious side effects from a medicine and others have none.

Pharmacogenetic testing provides information about your genes to help your health care provider choose the medicine and dosage that are the "best fit" for you. The tests use a sample of your saliva (spit), blood, or cells swabbed from your cheek.

Pharmacogenetic testing is a type of precision medicine. Precision medicine uses information about your genes, environment, and lifestyle to find out which approaches to disease treatment and prevention will work best for you.

Other names: pharmacogenomics, pharmacogenomic testing

What is it used for?

Pharmacogenetic testing may be used to:

• Find out whether a certain medicine could be effective for you
• Find out how much of the medicine you need
• Predict whether you will have a serious side effect from a medicine

Why do I need pharmacogenetic testing?

Your provider may order these tests before you start a certain medicine. You may also need a pharmacogenetic test if you are taking a medicine that's not working and/or causing serious side effects.

Pharmacogenetic tests are not available for all medicines. Examples of common medicines that have pharmacogenetic tests include:

• Abacavir, an HIV treatment
• Carbamazepine, an epilepsy treatment
• Tamoxifen, a breast cancer treatment
• Warfarin and clopidogrel, blood thinners

What happens during a pharmacogenetic test?

Testing is usually done on blood, saliva, or a sample of cells swabbed from the inside of your cheek.

For a blood test, a health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

For a saliva test, you will be instructed how to provide your sample. Usually, you will either spit into a small tube or your saliva will be collected with a special swab or pad.

For a cheek swab, a health care professional will gently rub the inside of your cheek with a special swab.

At-home test kits are available for certain pharmacogenetic tests. With a home test, you collect a saliva sample to send to a lab for testing. In general, these tests should not be used for making treatment decisions because they may not be accurate. Talk with your provider if you're considering an at-home test.

Will I need to do anything to prepare for the test?

You usually don't need any special preparations for a blood test. If you are getting a saliva test, you should not eat, drink, smoke, or chew gum for 30 minutes before the test. If you have a cheek swab, you may be asked to rinse your mouth first.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

There is no risk to having a saliva test or a cheek swab.

What do the results mean?

Your test results will describe any changes, called variants, in the gene that was tested. Changes in these genes can show how certain medicines are likely to affect you. But these gene changes do not tell you anything about your health condition.

Your provider will use the results of your pharmacogenetic test along with other information about your condition to recommend treatment or to make changes in your treatment. This includes suggesting which type of medicine is likely to work best in your body and how much you should take to get the most benefit. Your test results may also predict whether you're likely to have side effects.

If your test results show that a certain medicine isn't right for you, your provider will consider other treatments that may help you. Talk with your provider to find out how your test results may change your treatment options.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about pharmacogenetic testing?

Pharmacogenetic testing is not the same thing as genetic testing. Genetic tests that are done for health reasons can help diagnose diseases. They may also provide information about your risk for certain diseases. Pharmacogenetic testing cannot diagnose any conditions or tell you about your risk for developing them.