SCOTTSDALE - The accuracy of blood-testing equipment used by Scottsdale police in drunken driving cases is being challenged.

Hundreds of drunken driving cases from the past four years could be called into question if the legal challenge is successful, the Arizona Republic reported. The case could also affect the treatment of forensic evidence in Arizona courts.

Eleven felony DUI cases have been consolidated into an ongoing evidentiary hearing in Superior Court. The question is whether a crime lab technician's decision to use old software on a new blood-testing machine in 2009 has affected evidence handled by Scottsdale's crime lab.

Scottsdale police have declined to comment but issued a statement Friday saying the lab has been accredited since 1996 because its practices for maintaining equipment meet or exceed national standards.

Defense attorneys are questioning whether the lab should be accredited.

"We have a laboratory where the blood results are being used to decide whether people go to jail or prison. For the last going on four years now, at least once a month, every month, there's some huge error where there's an unexpected result," said Joseph St. Louis, a Tucson attorney involved in the case.

St. Louis said the crime lab has yet to solve the problem to ensure results are accurate.

Court documents indicate police have been aware of potential problems with the blood-testing equipment for years. For example, the equipment mislabeled vials with wrong names or numbers, quit running during tests and erased baseline information from measurements during test runs.