Read This Before You Buy a Genetic Testing Kit

How it works: To determine whether you might be related to another person in its customer database, a DTC testing company considers how many identical segments of DNA you have in common and the length of those segments. The closer the relative, the more large DNA segments you’ll share.

“For close relationships, those predictions can be made very accurately,” says Debbie Kennett, a genetic genealogist in the U.K. who helps people construct family trees using DTC testing and traditional methods, such as digging into historical records.

For instance, “relative matching” tests will always work with a parent or full sibling, she says. The further away a relative is on the family tree, however, the less certain the results. “If you share, say, 25 percent of your DNA, then there’s a wider range of possible relationships,” Kennett says. Still, 23andMe, for example, says that its test on its own will accurately detect relatives as distant as third cousins about 90 percent of the time.

The drawbacks: While a test might unearth a previously unknown cousin who becomes your new best friend, you could also learn something negative or even shocking about a family member or relationship. In CR’s survey, 9 percent of respondents who used these tests said their reports contained unsettling information, such as news that someone thought to be a biological relative—like a father—isn’t genetically related.

An unexpected discovery about a relative is one of the most frequent surprises for users of DTC genetic tests, says Anita DeLongis, PhD, a professor in the department of psychology at the University of British Columbia in Vancouver, who is studying the effects these products have had on people’s lives. Many of her study subjects, she says, “had not anticipated learning a family secret.”

How it works: Companies such as Ancestry and 23andMe say they can tell you the regions—and sometimes even the countries—where your ancestors originated, based on your DNA. In CR’s survey, curiosity about ancestry was the most common reason for taking a DTC genetic test, listed by about two-thirds of respondents.

Finding relatives involves comparing your DNA directly with other people’s in a database, but estimating your genetic ancestry is more roundabout. One common strategy looks for variations in your genetic code that have been found to be statistically more likely in people from certain regions. The testing company then gives you an estimate of the percentage of your DNA that comes from such areas. For example, your result might show that 40 percent of your DNA comes from Europe and 60 percent comes from Asia.

The drawbacks: It’s hard for testing to pin down genetic ancestry accurately for several reasons. Different test makers may rely on different sets of data, including, often, some from their own customers—which can skew findings. Also, the fewer samples a company has from a certain region, the more limited its ability to tell you whether you have ancestors from that area. On the flip side, as more people take one company’s test, its pool of information should become larger and better. That can cause the strange phenomenon of having your genetic ancestry test results change over time as a manufacturer widens its “reference database.”

Another concern: The databases often have genetic details on people whose families came from a particular region in the recent past. But ancestry stretches back much further than, say, our grandparents. “It’s not always clear that the population you’re being compared to is the same one that was in that location several hundred or thousand years ago,” says the University of Pennsylvania’s Wendy Roth.

It’s important to remember, too, that although a given gene variant may be more common among one group of people, it can also appear in others. So finding a particular variation in your genetic code doesn’t definitively place you in any one regional, ethnic, or racial group. What all this means for consumers, according to Mwenza Blell, PhD, a biosocial medical anthropologist at Newcastle University in the U.K., is that genetic ancestry tests are closer to palm reading than science.

This testing also has an unintended social consequence, experts say. Because country-of-origin labels closely overlap with commonly used ethnic and racial labels, the test can reinforce the mistaken idea that your ethnicity or race is encoded in your genes.

In reality, the mapping of the human genome demonstrated that all people are more than 99 percent the same genetically, regardless of race or ethnicity. This finding represented a major milestone for scientists and historians who had been working to dismantle the idea that racial categories—an invention of modern history—were biological rather than social.

The emergence of DTC genetic testing and its focus on genetic ancestry has proved to be a major and unexpected setback to this work, Blell says, by reinscribing notions of biological differences among races.

A 23andMe representative told CR that it has worked to dispel these notions, “including noting in our reports the results are based on recent ancestor locations.” Ancestry did not provide a comment on this by press time.

How it works: Some manufacturers say that their tests, using research about variants associated with various conditions, can help assess whether you are more likely to develop a disease such as breast cancer or Alzheimer’s.

The company 23andMe does this using technology for which it has received approval from the Food and Drug Administration, allowing the firm to sell the test directly to you. Others use what’s known as physician-mediated tests. Once you purchase such a kit, the company enlists a doctor—generally one who is associated with the test maker and does not meet with you directly. This lets the manufacturer offer the test without FDA approval, as long as it is analyzed in a federally certified lab, says Katie Stoll, executive director of the Genetic Support Foundation, a nonprofit that provides genetic counseling services.

The drawbacks: The picture of your disease risk that you get from a DTC genetic kit might be less complete than that of a test you get as part of your regular medical care.

In contrast to at-home testing, your own healthcare providers will generally work with you closely to determine whether you need certain tests, based on your health history and your family’s. They’ll also pair you with licensed genetic counselors, who can help ensure that you’re tested for all potentially relevant genetic variants and that your testing will be covered by insurance.

And DTC disease-risk tests might not include a wide range of important gene variations. Take, for instance, 23andMe’s test for variants of the BRCA1 and BRCA2 genes, which have been linked to a higher risk of breast and ovarian cancer. The company’s test looks for three specific variants that have been well-studied and are most common among people of Ashkenazi Jewish descent. But thousands of additional variants of these same genes are also known to cause breast and ovarian cancer, including certain variations that occur more frequently in other populations, according to genetic counselor Kelly Ormond, a professor in the department of genetics at Stanford University School of Medicine in California.

What this means: A negative result may provide a false sense of relief because it doesn’t look at all the variants, Ormond says. Also, while DTC test makers often offer genetic counseling, a company counselor will be less familiar with your medical history than a counselor your doctor refers you to, Brothers says.

23andMe says it clearly explains test limitations to users, noting prominently on its website that its BRCA1 and BRCA2 results, for example, are for only three variants of those genes.

How it works: A number of DTC testing companies currently offer personalized diet recommendations based on your genetics. Some draw their advice from existing studies, such as those on how, for instance, a specific genetic variation may be linked to a better response to a certain diet or exercise program.

The drawbacks: The prospect of incorporating genetic information into dietary advice is exciting because it could allow dietitians to better tailor advice to individuals’ needs, says Amy Ellis, PhD, an associate professor in the department of human nutrition at the University of Alabama in Tuscaloosa.

But far more and better evidence is needed. Right now, the dietary advice from DTC companies may be based on incomplete evidence or could yield misleading conclusions, according to recent research. When a 2020 study in the journal Nutrients evaluated 45 DTC services offering personalized nutritional advice, it found a number of worrisome practices. For example, the authors say that more than 900 genetic variants may contribute to a person’s risk of obesity. Yet companies often provide weight-loss advice based on just a handful of variants.

What’s more, much of the research about gene variants and diet is observational and hasn’t been adequately replicated in other studies, says George Hindy, PhD, assistant professor of population medicine at Qatar University in Doha. Such research can suggest an association only between a variant and an outcome such as faster weight loss, not a cause-and-effect relationship.

When it comes to a good diet, “genes . . . are not a definitive answer,” says Yi Sherry Zhang, PhD, the founder of GenoPalate, which provides dietary advice based on genetic testing. “We need a holistic approach.”

So, what should you do? In the end, DTC genetic tests can provide certain insights, but it’s important to be aware of their limitations. And keep in mind that your genetics are only one element of your overall well-being: Your environment, healthcare access, and behavior are also important, says James E. Rogers, PhD, CR’s director of food safety research and testing.