Wouldn’t it be great if there were some sort of test you could take to predict which medications are likely to work best for you and which could hurt you with an adverse reaction? Good news: There is such a test, and it’s not some out-of-reach possibility for future use – it’s starting to pop up at medical centers around the country. These tests are known as PGx (pharmacogenetic) tests; they are DNA tests that look specifically at the genes that predict a person’s drug responses. Just as your genes determine traits like eye color and whether you have dimples or freckles, they also influence the way you will react to medications.
What PGx Tests Are – And Are Not
PGx tests use a small sample of a patient’s blood or saliva to sequence genes involved in processing medications. When you take a medication, your body uses enzymes; specialized proteins, to break down the drug. Though the body makes thousands of enzymes, a small number are particularly important in drug metabolism, each interacting with several different drugs. For example, an enzyme called CYP3A4 breaks down the benzodiazepine Valium, the antibiotic erythromycin, and the statin Lipitor.
PGx tests look at the genes that tell a person’s body to produce enzymes like CYP3A4. This is important because people who are genetically disposed to make fewer enzymes can’t break down drugs fast enough and can suffer from adverse reactions and side effects. Other people produce unusually high levels of enzymes which can create problems as well. For example, the drug tacrolimus is an immune suppressant prescribed to patients who undergo organ transplants. Patients who metabolize this drug too quickly don’t get the full effect required to minimize the risk of rejecting their transplanted organ. A PGx test can warn their doctor that they will need a higher dose of the drug.
Limitations
There are limitations to pharmacogenetic tests. While fortunately these tests are applicable to about 80 to 90% of available drugs (to varying degrees), there are still medications for which tests are not available. In addition, if a genetic test predicts you will respond to a drug normally, it doesn’t guarantee you will not experience an adverse event. Lastly, though PGx testing is already available in some places, it isn’t yet widespread, and insurance coverage is still limited. “PGx testing is an emerging field, so many insurance plans have not started covering it,” notes Dr. Jalloh, PharmD, assistant professor at Touro University California and spokesperson for the American Pharmacists Association.
Does Insurance Cover It?
Medicare does pay for the test, but only under certain circumstances. “Medicare will cover the test with ‘medical necessity’ which may include disease states, prior history of adverse drug reactions, or documentation from a doctor that someone is not responding to typical doses of medication,” says Ken Sternfeld, Remote Care Pharmacist at www.pharmacist.care. Commercial insurers are taking it slower: In an analysis of the top private insurers in the US (covering about two thirds of the United States population), only 20% of the most common PGx tests were covered by insurance. The tests that were covered were typically those related to cancer drugs.
Coverage may expand as awareness about the test continues to grow, especially as studies show that close to 100% of people carry at least one gene variant that could be used to improve their choice of medication or dosage. Some good news: In 2019, the nation’s largest insurer, UnitedHealthcare, expanded its coverage of PGx testing to include tests targeting mental health medications.
Here are 5 more things you should know about PGx testing
- It is likely that the results from a PGx test you take now will be applicable to a medication you take in the future. Many commonly prescribed drugs interact with only a small number of genes, so taking the most common genetic tests once can cover you for future prescriptions. Make sure that your healthcare providers are sharing the results with all of your doctors and pharmacists.
- The test is very quick. The test itself takes 2 minutes, but it can take anywhere from 1 to 14 days for a lab to process it and provide results. “Certain medications may be started in the meantime to avoid the risks of treatment delays,” says Dr Jalloh.
- PGx tests are currently available for over 250 commercial drugs, including many FDA “boxed warning” drugs for which the test is required or highly recommended. These medications have been linked with serious or life-threatening side effects. The Clinical Pharmacogenetics Implementation Consortium maintains a list of PGx tests which designates which are most highly recommended. The tests for medications at the top of the list have the greatest amount of evidence supporting their use thus far.
- Testing can save you time and money. “There is a huge savings in patient healthcare costs as it eliminates trial-and-error prescribing, plus the costs of hospitalizations for adverse events,” Sternfeld says.
- Certain medical centers are more likely to offer testing than others. University hospitals with programs that focus on pharmacogenomics are likely to offer the testing. “Also, some pharmacy schools are leading the way in research and training, therefore hospitals or clinics affiliated with the school may be possible choices for testing,” states Dr. Jalloh.
What to Ask Your Doctor
In general, patients should ask their pharmacist if any of their current medications may work differently based on one’s genetic makeup, Dr. Jalloh suggests. “Patients should ask for this evaluation anytime their pharmacist does a comprehensive medication review or medication check-up.”
This article was originally published Jan 11, 2018. It was updated by Joyce Clanon on May 10, 2022.
