The US Attorney's Office, Western District of Pennsylvania alleged the doctors received improper payments for referrals from drug testing lab Universal Oral Fluid Laboratories.
In addition to lower reimbursements, Ameritox also faced a fraudulent claims lawsuit from Humana.
The OIG recommends that CMS direct Medicare contractors to recover the improper payments from providers and strengthen system edits to prevent further improper payments.
By dropping the cutoff value in urine immunoassay testing to 20 from 100, the researchers reduced the false-negative rate to 2 percent from 47 percent.
Dominion Diagnostics will pay $815,000 to settle allegations by the US Attorney's Office and Vermont that it improperly billed for tests.
Pacific Toxicology Laboratories has expanded its menu to include fentanyl and its analogues as deaths surge from synthetic opioid overdoses.
The test, which is based on the company's beta-galactosidase enzyme technology, is cleared for the qualitative detection of fentanyl in urine.
The accreditation covers postmortem and human performance toxicology analysis, including driving under the influence of drugs and alcohol testing.