BOSTON – For several years, attorney Steven Panagiotes has challenged the machines used by state and local police to test drivers’ blood-alcohol levels, arguing that technical problems render the gadgets unreliable.

The Fitchburg personal injury lawyer says the machines used by police across the state to determine if someone is driving drunk — the Draeger Alcotest 9510 — have calibration problems. State officials have known about them for nearly a year, he said.

“Obviously something is malfunctioning with these machines, and they’re being secretive about what problems they’ve found,” Panagiotes said. “If the calibration isn’t good, then the results aren’t going to be good.”

Test results from the Draeger machines, which have been in use by police across the state for about five years, are now the subject of an investigation by State Police and the Executive Office of Public Safety and Security. The state agencies are reviewing DUI cases dating back years for evidence of questionable results, according to state officials. About 70 of nearly 6,000 DUI cases involving breathalyzer tests are reported to have been flagged as questionable so far.

In Essex County, at least five cases dating as far back as 2011 have been identified as possibly being affected. Prosecutors in Middlesex and Suffolk counties have identified another dozen cases that could be affected.

The Massachusetts Bar Association this week called on Attorney General Maura Healey to conduct an independent investigation.

“This is an important issue and we need to maintain the integrity of the process,” said Marsha Kazarosian, the bar association’s president. “It’s about transparency, fairness and constitutional rights. Seventy cases may not sound like a lot, but it is. And where there’s smoke there’s fire. There may be more cases affected.”

On Thursday, Suffolk County DA Daniel Conley directed prosecutors to postpone pending DUI cases involving the blood-alcohol tests until the state completes its review. Conley ordered devices in his district to be recalibrated and said he would undertake a review of convictions based on evidence from the new machines.

“While we have no reason to believe that the very small number of affected Suffolk cases will increase, we have every reason to seek certainty that past convictions are based on reliable evidence,” Conley’s spokesman Jake Wark said in a statement.

Meanwhile, district attorneys in Middlesex and Essex counties and on Cape Cod and the Islands have suspended the use of blood-alcohol tests as evidence in drunk driving cases until State Police conclude their investigation.

Numerous problems could produce false results in a blood-alcohol test, said Peter Elikann, a Boston criminal defense attorney and vice chairman of the Massachusetts Bar Association’s Criminal Justice Council. Those might include mechanical errors or improper calibration by law enforcement officers who prepare the machines for use in the field.

“Even under the best of circumstances, these devices are not 100 percent accurate,” he said.

Public safety office spokesman Felix Browne said in statement that the state’s investigation is meant to “ensure the integrity” of the testing method, pointing out that breath testing is “one of the most accurate and reliable tools we have to identify and investigate drunk drivers.” Browne said the review is expected to be complete next week.

In March, the Office of Alcohol Testing, which certifies the results of blood alcohol tests given throughout the state, sent a letter to district attorneys with a list of cases where the calibration of the machines fell below levels required by law. At least in the Suffolk County cases, Wark said, calibration tests of the machines gave readings that met the manufacturer’s guidelines but fell outside stricter limits required by the state.

The Draeger machines, which cost up to $10,000 each, estimate the level of alcohol in an individual’s blood based upon a breath sample. To verify that readings are accurate, the machines are supposed to be frequently calibrated using a “dry gas technique,” which involves releasing a mixture of alcohol and nitrogen from a pressurized canister into the machine.

A spokeswoman for the German company’s U.S. operations didn’t return phone calls seeking comment.

Defense attorneys are demanding that the state release more details about problems with the machines.

“This information needs to be distributed so that those attorneys representing clients that have cases involving the Draeger Alcotest 9510 to have all the information available to enable them to zealously represent their clients,” said John Morris, an attorney with the Essex County Bar Advocates Inc., a public counsel service, in a letter to the Essex County DA’s Office on Wednesday. “This information is potentially exculpatory and needs to be produced immediately.”

Panagiotes said he’s pressured the state to release the operating manual for the machines. He argues that it should be available to defense attorneys, though the state has refused to provide it.

State Police spokesman David Procopio said troopers are still using the devices to test DUI suspects, but the agency has advised field offices on proper procedures for calibrating the machines to ensure they are functioning properly.

“As far as we know, its an issue of improper calibration,” he said. “But the testing will determine how widespread the issue is or if there even is an issue.”

He said law enforcement officers rely on evidence other than blood-alcohol tests, such as observation and field sobriety tests, to determine if a motorist is impaired.

The legal limit in Massachusetts is a blood-alcohol content of 0.08 for adults – or 0.02 for drivers under 21. Motorists suspected of driving under the influence can refuse to take a blood-alcohol test, but that results in an automatic suspension of a driver’s license.

Panagiotes said blood-alcohol tests weigh heavily in DUI cases, often resulting in a guilty verdict.

“Most jurors think Breathalyzers are infallible, so defendants are essentially tried by machine,” he said.

Nearly 13,000 people were arrested for drunk driving in Massachusetts in 2014, according to state records.

Elikann said he expects a number of DUI cases to be called into question as a result of the investigation.

“When you have this kind of questionable evidence, I think retrials are going to be inevitable in a number of these cases,” he said. “Especially in cases where defendants plead guilty when faced with breathalyzer evidence.”

The Salem (Mass.) News reporter Julie Manganis contributed to this story. Christian Wade covers the Statehouse for CNHI’s Massachusetts newspapers.