Medicare and other insurers pay for urine tests with the expectation that clinics will use the results to detect and curb dangerous abuse. But some doctors have taken no action when patients are caught misusing pharmaceuticals, or taking street drugs such as cocaine or heroin. Federal pain guidelines say doctors should discuss test results with patients and taper medication if necessary.

Medicare and private insurers acknowledge that they lack the resources to routinely verify that doctors who order a high volume of drug-related tests do so to improve patient care, not fatten the bottom line.

“This is a big issue,” said Louis Saccoccio, who heads the National Health Care Anti-Fraud Association, a group formed by private insurers and government officials. “There are abusive practices out there.”

In nearly a dozen recent criminal cases, prosecutors have cited evidence that doctors supplied opiates to patients with repeated abnormal urine test results.

One such doctor was Alabama pain specialist Shelinder Aggarwal, who billed Medicare and private insurers over $9 million for urine tests solely “because he served to profit,” according to prosecutors in Alabama. He pleaded guilty to illegal prescribing and health care fraud. Earlier this year, a judge sentenced him to 15 years in prison.

Theodore Parran, who has served as an expert witness for the federal government, predicted more doctors could face fraud charges, or discipline by state medical licensing boards, over lab testing that appears to be profit-motivated.

“This is certainly on their radar,” Parran, a professor of medical education at Case Western Reserve University School of Medicine, said in an interview. Ignoring repeated abnormal urine tests “is bad medicine” that “endangers the safety of the patients and the community.”

The Kaiser Hospital News investigation earlier this year found that dozens of pain doctors with their own labs took in $1 million or more in 2015 from Medicare for running urine and, in some cases, genetic drug tests. Some doctors derived at least 80 percent of their Medicare income this way.

Indeed, deciding how often to order these tests, and for which patients and drugs, can be a judgment call. Doctors also sometimes disagree over what action they should take against patients with “dirty” urine: Some doctors kick out drug abusers, while others argue that is unethical. Instead, doctors should counsel these patients and refer them for substance abuse treatment, they say.

Donald White, a spokesman for the U.S. Department of Health and Human Services’ Office of the Inspector General, said if test results are disregarded, “why is the test being ordered in the first place?”

“When abnormal urine drug test results are not acted upon by the physician who ordered the test, it raises concerns not only that the testing itself is not medically reasonable and necessary, but also that the doctor’s treatment of the patient may fall below the standard of care,” White said.