LANSING, Mich. (AP) — The Michigan State Police say about 3,250 lab reports on THC toxicology samples in prosecutions may be inaccurate because of a technical issue.

The state police Forensic Science Division said Wednesday that the problem may impact cases that occurred as far back as March 28, 2019.

It’s not clear whether any convictions may be overturned as a result. Individual cases in which the problem might have occurred “are being identified and will be shared with the prosecuting attorney of record for further investigation as to any potential impact to the individual involved,” the division said in a news release.

As a result of the discovery of the problem, the Forensic Science Division said it has temporarily halted the disposal of blood samples to preserve the evidence should re-analysis be required; has started validating a new cannabinoid confirmation method that will distinguish CBD from THC; and started the process to establish a contract with a private, accredited laboratory for processing THC samples for the time being before the new method is validated.

THC is the compound that gives marijuana its high. Samples containing CBD, also known as Cannibidiol, may be converted to THC during the problematic testing process, state police said.

CBD is also found in marijuana and is structurally similar to THC, but it doesn’t cause a high. It often is sold as a dietary supplement or included in creams and other personal care products. CBD products are legal, with some restrictions, in almost all states.

The Forensic Science Division began evaluating its testing process on Aug. 19 and a spokeswoman for the State Police crime lab said last week that that it stopped screening blood samples for THC after a “discrepancy” in the lab was discovered in which the presence of CBD might have led to a positive result.

Since 2018, marijuana has been legal under state law for people who are at least 21. Medicinal use was approved 10 years earlier.

It’s still illegal to drive under the influence of marijuana but Michigan, unlike some other states, has no established limit. In 2019, a commission recommended against creating a threshold because of a “poor correlation” between bodily content and driving impairment.

Nevertheless, prosecutors still can present evidence of THC in court.