SAN ANTONIO -- Local defense attorneys are questioning the county's use of a new drug testing lab to test probationers.

The group claims they've been contacted by several people who work within the criminal justice system and are concerned about what they call a significant increase in false positive test results.

Bexar County recently switched over to a new lab, which has caused a number of defendants to reportedly test positive, resulting in probation revocation.

"What we want the public to know is that individuals within the system believe there are people going to prison for false positives on their drug tests," criminal defense attorney Jimmy Parks Jr. said. "Right now, we need something done about it very quickly."

There has indeed been an increase in positive tests, said Bill Fitzgerald, the head of the Adult Probation Department, because the tests are now more sensitive and accurate than ones used in the past.