Pharmacogenetic Tests

Pharmacogenetics (also called pharmacogenomics) is the study of how your genes affect the way your body responds to certain medicines. Genes are parts of DNA in your cells that you inherit from your parents. You inherit two copies of each gene, one from each parent.

Genes carry information that controls what you look like and how your body works. Some genes also affect how your body uses and breaks down medicines. For example, certain changes (or variants) in these genes may make it harder for your body to absorb a certain medicine or dosage.

Because your body can't absorb it, the medicine won't work as expected. These genetic differences can be the reason why some people may benefit from a certain medicine while others may not benefit at all. They may also be the reason why only some people have serious side effects.

Therefore, before treating you, your health care provider may want to see if you have any gene variants that may affect your response to certain medicines. To do this, they will use pharmacogenetic testing, which looks for these gene changes in a sample of your blood, saliva (spit), or cells swabbed from your cheek.

Why this test is done

Pharmacogenetic tests are not available for all medicines or used for all health conditions. Providers most often rely on pharmacogenetic testing when considering the following health conditions:

• High cholesterol. If you have certain variants of the SLCO1B1 gene, you're more likely to have muscle pain and weakness when taking some statins such as atorvastatin and fluvastatin.
• Depression. If you have certain variants of the CYP2D6 or CYP2C19 gene, you're more likely to have trouble breaking down some antidepressants such as sertraline and venlafaxine.
• Blood clot prevention. If you have certain genetic variants, you're more likely to need lower doses of the anticoagulant medicine warfarin.
• HIV. If you have a certain variation of the HLA-B gene, you're more likely to have a severe skin reaction to Abacavir. A certain variant of the CYP2B6 gene can affect your nervous system if you take efavirenz.
• Multiple sclerosis. If you have certain variants of the TPMT or NUDT15 gene, you're more likely to have suppressed immune system responses if you take azathioprine.

When treating breast cancer, colon cancer, or acute lymphoblastic leukemia (ALL), your provider may use pharmacogenetic testing to make specific treatment decisions. For example:

• Trastuzumab only works for people with a kind of breast cancer that makes too much of the HER2 protein.
• Typical doses of mercaptopurine used to treat ALL can cause severe side effects if you have a certain variant of the TPMT gene.
• Irinotecan treatment for colon cancer can cause severe diarrhea and increased infection risk if you have a certain variant of the UGT1A1 gene.

You may also need a pharmacogenetic test if you are recovering from an organ transplant or taking a medicine that's not working and/or causing serious side effects.

Pharmacogenetics is a growing field of medicine. This means that, in the future, genetic testing may be used more frequently to make treatment decisions.

How to prepare

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.

Sample type

Blood Saliva

Other names for this test

pharmacogenomics, pharmacogenomic testing