MOUNTAIN VIEW, Calif. — As more people get genetic testing to assess their risk of getting cancers and other serious conditions, diabetes has been almost entirely left out — largely because of the difficulty of developing a useful test.

But at the South by Southwest festival on Sunday, the consumer genomics giant 23andMe announced that it will now tell its customers how their DNA affects their chances of developing type 2 diabetes, a condition better known for its link to environmental factors than genetics.

23andMe’s new report will be available online on Monday for no additional cost to most of its existing customers, as well as any new customers who trade in $199 and a saliva sample for those and a whole host of other results.

The new test moves 23andMe into a disease projected to affect two-fifths of America’s population of adults in their lifetime. But it’s not at all clear whether it will provide additional value beyond the benefit conferred by existing screening programs that simply query people about things like their lifestyle habits and their family history.

Such questionnaires and genetic testing “haven’t been compared head to head, and so it’s unknown whether or not genetic screening would pick up patients earlier or more patients who either have prediabetes or diabetes,” said Dr. Tom Donner, director of the Johns Hopkins Comprehensive Diabetes Center.

23andMe built the test using genetic data from more than 2.5 million of its customers who’d agreed to participate in research. The test analyzes over 1,000 genetic variants to generate what’s known as a polygenic risk score, which can be thought of as a sort of genetic credit score. It then adjusts that score based on a customer’s self-reported ethnicity and age.

A 40-year-old who identifies as Latina, for example, might be told she has a 79 percent chance of developing type 2 diabetes at some point in the next four decades.

The company said it determined that it does not need clearance from the Food and Drug Administration to market the test; instead, it developed its new report by following the FDA’s guidance for developing products meant for wellness. The FDA has previously authorized 23andMe to sell risk assessment tests for breast cancer, Alzheimer’s, and Parkinson’s, among other conditions.

In its new diabetes risk report, 23andMe takes pains to distinguish between genetic risk and overall risk, the latter of which can be influenced by lifestyle. 23andMe’s report urges its customers to take action with commonsensical tips like “maintain a healthy weight,” “get active,” “eat healthy,” and “don’t smoke” — sound advice for just about anyone, regardless of their genetic risk of developing diabetes.

The report also encourages customers to talk to a clinician, who might provide a diagnosis, or to consider a diabetes prevention program. It links to a service offered by Lark Health, a Silicon Valley chatbot coaching service with which 23andMe struck a deal in January. Lark’s diabetes prevention program costs $20 per month for people whose insurers won’t cover it.

When 23andMe launches the new report, “a bunch of people are going to find out that they’re at increased risk,” Emily Drabant Conley, the company’s vice president of business development, told reporters at a briefing last week at the company’s Silicon Valley headquarters. “So this may prompt them to go take action where they can actually get diagnosed.”

23andMe’s test is for consumers, but there are good reasons why diabetes genetic risk assessments haven’t yet been adopted in clinical care, Donner said.

“Until genetic screening has been shown to improve the detection of patients with diabetes above and beyond the standard of care, physicians aren’t going to be looking to order tests whereby there’s a cost without knowing that there’s going to be a benefit,” Donner said.

Dr. Robert Gabbay, chief medical officer at the Joslin Diabetes Center in Boston, said he thinks only time will tell whether 23andMe’s test sends at-risk patients to see a physician who wouldn’t otherwise do so. But he welcomes the potential.

“We need to find ways to encourage them to make sure they get screened for diagnosis,” Gabbay said. “Anything that increases the probability of that, the better.”