A medical supply company mistake threatens to complicate hundreds of drunken driving cases in Texas. An NBC 5 investigation has found blood alcohol level test tubes recalled by the manufacturer have been used in at least 2,760 DWI arrests across the state.

The recalled tubes have raised concerns among law enforcement officials and defense attorneys that some accused drunken drivers could walk free, or that others could be wrongfully convicted.

Blood testing has become the gold standard for prosecuting drunken driving cases in Texas. But some of those tests are now clouded in confusion after the maker of the most popular blood alcohol test tubes, BD, recalled a lot of 247,000 tubes in 2019 because of concerns that a small number of tubes within that lot were missing a preservative powder. The preservative is supposed to ensure that the blood alcohol level does not change before the blood in the tube is tested at a lab.

“These are the kinds of things that make everybody question what's going on,” said Dr. Peter Stout, president, and CEO at the Houston Forensic Science Center.

Stout also heads the Texas Association of Crime Lab Directors in addition to running Houston’s crime lab - where he said alarm bells went off when staff first saw the recall notice in 2019.

In the notice, BD urged people who had purchased the grey topped tubes to "immediately review" their inventory and "return all" tubes subject to the recall.

But by the time that warning arrived in many Texas cities, the recalled tubes were already in the hands of local police.

“There's no question some of these were used in actual cases. And that has created some real issues for us and for the entire court system,” said Stout.

To find out how many were used in actual cases, NBC 5 Investigates surveyed area police departments and district attorney’s offices in the DFW area along with some other large law enforcement agencies across the state.

So far, the NBC 5 search has identified at least 2,760 cases where a recalled tube was used in the arrest of a suspected drunken driver. Many of those cases are just coming to court now, two years later, because of a backlog of cases stemming from the COVID-19 pandemic.

Arlington's police department is one of many that received tubes from the recalled lot.

“In 61 cases, we use these blood test kits thinking we're doing the right thing,” said Arlington Police Chief of Staff, Chris Cook. “It's frustrating. I know our officers … they were disheartened to learn that this is another issue we have to deal with."

“We don't want a defendant getting off on a technicality because someone says the evidence is unreliable,” Cook said.

The Texas Department of Public Safety also told NBC 5 Investigates its crime labs have tested blood in at least 290 cases where recalled tubes were submitted to DPS labs by police departments across the state.

NBC 5 also identified 49 cases where recalled tubes were used to collect blood even after DPS had warned local police departments about the recall.

If the preservative powder in the tube is missing, scientific studies have shown the blood alcohol level would most likely come down.

It would only increase in a rare set of circumstances. So, a tube without a preservative would more likely hurt the prosecution than someone arrested.

But BD's recall notices have said the blood alcohol level could be "either falsely low or falsely high" if the preservative is missing. A statement that defense attorneys may jump on to challenge the results.

“I expect them to use it very aggressively. They're going to use it to suggest that something might have happened. They're going to use this to suggest that the system's not perfect," said former Tarrant County DWI prosecutor, Richard Alpert.

Alpert fears with jammed courts, prosecutors might decide some of the cases involving recalled tubes are not worth the extra time.

“There is an unprecedented backlog of cases throughout the state and cases do not get better with time. So, I would not be surprised if some of them do plea bargain those cases down or get rid of those cases,” said Alpert.

Stout said he’s already aware of cases dismissed and others where prosecutors are still debating what to do.

“I know we've got cases out there that actively have this discussion going on. It's frequent enough to be a problem,” Stout said.

NBC 5 Investigates has learned dozens of notices are also being sent to people convicted of drunken driving in the DFW area notifying them that recalled tubes were used in their case and opening the possibility that some cases could be appealed.

The Tarrant County District Attorney’s office sent some of those post-conviction notice letters to defendants in just the last two weeks.

DWI defense attorney, Mimi Coffey believes all recalled tubes should have been tossed out and not tested at all. She points out one of the notices BD issued about the recall in 2019 urged users to "destroy all" tubes affected.

But when the Texas Department of Public Safety sent out its own notice about the recall in 2019 it told local police to "submit specimens expeditiously," "especially if your kits are associated with the recall."

“The manufacturers said that if you don't have it tested within two days, destroy it. These defective tubes and of course, Texas DPS is saying just the opposite,” said Coffey.

In a written statement, DPS told NBC 5 it believed blood collected in recalled tubes should have still been tested.

"The likelihood of blood alcohol concentrations being elevated due to the lack of additives ... is extremely unlikely,” the statement said.

And lab directors told NBC 5 Investigates they must test the blood collected, even if it’s in a recalled tube.

“It is a piece of evidence in a crime. We don't really have a choice but to try and do something with it,” said Stout.

But Stout said BD’s handling of the recall has made it harder for lab experts who testify in DWI cases.

BD initially said it believed only about 300 of the 247,000 recalled tubes were missing preservative powder.

But in a recent email to Stout's staff, BD said 1,500 tubes may have been impacted by the missing powder.

“So I can't even really answer the question of how likely it is that there was a tube that might not have had the preservative in it because that number keeps changing,” said Stout.

BD declined to speak to NBC 5 on camera but provided a written statement saying it takes its "responsibility to provide quality products very seriously."

A spokesman for the company wrote in part, "This issue occurred in 2019 and the manufacturing issue was immediately corrected."

BD confirmed that only 1,500 of the 247,000 recalled tubes were missing the preservative and the company said it recovered nearly 200 of those tubes before they were used.

But without knowing where the remaining tubes ended up, prosecutors and defense attorneys are now left to argue in court about what should happen.

“Everybody deserves to have that chance. They need to know whether or not that blood can be relied upon and then decisions made afterward,” said Coffey.

“The important thing for prosecutors and law enforcement is to be prepared for those attacks and to have a response and to make sure your expert knows it's coming,” said Alpert.

Alpert said police should always check the tube before collecting the blood and then note on the police report that the officer witnessed the powder in the tube. That information will help if there is a question later, Alpert said.

Alpert created a checklist that is used by many Texas police departments and the list includes checking each tube for preservative powder before obtaining a blood sample.

But NBC 5 reviewed police reports in cases involving some of the recalled tubes where officers did not note whether the power was present, which could complicate the situation for prosecutors if that case is challenged or appealed.

By now the tubes affected by the recall have reached their expiration date. So if police officers check the expiration date, they would be able to avoid using any remaining tubes that were part of the recall.