Defense lawyers, prosecutors and other attorneys are preparing to review hundreds of criminal and civil cases after the Broward Medical Examiner’s Office reported a crucial flaw in how it conducted toxicology tests in DUI cases involving alleged drug use.

Broward Medical Examiner Craig Mallak told State Attorney Mike Satz on Tuesday that his office improperly validated its drug testing procedures in all cases that went through the ME’s office before Aug. 24, 2012. Mallak told Satz he immediately shut down his lab and referred new cases to an independent laboratory.

Mallak said he could not tell how far back the problem dates or how many cases may be affected.

The improper procedure was performed when testing for, among dozens of other drugs, cocaine, heroin, oxycodone, hydrocodone, marijuana, amphetamines, Valium, Xanax, sleeping pills and other over-the-counter medications that affect a user’s ability to drive.

“This could be a pretty big deal,” said Kenneth Hassett, president of the Broward Association of Criminal Defense Lawyers. “If you have an old case that was a DUI manslaughter, and in that case the person tested positive for cocaine or heroin or something, a drug, it was then sent to this lab, and the tests were not validated. That evidence is inadmissible.”

Not on the list, Mallak said, was alcohol or PCP, commonly known as Angel Dust. Procedures to test for those substances were conducted properly, he said.

Immediately after learning of the flawed procedure, Satz contacted Hassett and Broward Public Defender Howard Finklestein, asking them to spread the word to their colleagues and clients.

In an interview Wednesday, Mallak said that while he would not necessarily doubt the results of drug testing conducted out of his office before Aug. 24, the failure to validate the procedure would give lawyers a legal basis to question them.

“I would question all of them,” Mallak said, “because they arose without using the appropriate method validation to start with.”

Mallak, whose tenure as Broward Medical Examiner started in July, said he discovered the problem while preparing to improve the office’s professional standing by seeking accreditation from the College of American Pathologists, which would subject the office to a rigorous outside review.

Officials have no way of knowing at this stage how many cases may be affected by Mallak’s revelation. Already, prosecutors have been instructed to review their pending cases to make sure issues are resolved before trial.

“If they have a case where toxicology was done by the Medical Examiner’s Office, they have to alert the defense,” Satz said.

Pending cases are salvageable, said Mallak, because the blood and urine samples obtained to perform the tests are still at the Medical Examiner’s Office. Mallak sent 50 pending cases to the University of Florida for independent testing to verify the results, and more independent testing is expected.

But even if the independent tests validate the initial results on pending cases, there’s still the problem of closed cases in which the fluid samples have been destroyed. Mallak said his confidence in the tests’ accuracy may not meet the legal standard to be used as evidence in a criminal trial.