D.C. police have been working for nearly two months with only one of the eight machines the department uses to measure the blood-alcohol content of suspected drunk drivers, complicating prosecutions and possibly slowing the number of arrests.

The problem arose after the only city employee trained to test the accuracy of the devices, known as Intoximeters, quit early in the summer, officials said. Because the devices require regular certification for the results to be allowed in court, several had to be taken offline.

The only Intoximeter in use is in a police station four miles north of downtown. Officers also can take suspects for urine or blood tests — a more cumbersome process.

“We haven’t made DUI arrests in large numbers” since July 26, when the machines were deactivated, said Master Patrol Officer Ben Fetting, the D.C. police union’s chief shop steward at the 3rd District station.

District officials said that they have hired a new supervisor and trained additional staffers to calibrate the machines, and that three additional Intoximeters will be running this week, with the remainder to become operational in early October. The breath-testing program is run by the Office of the Chief Medical Examiner, which has forensic experts.

Police said that between July 26 and Tuesday, D.C. officers made 179 arrests in suspected cases of driving under the influence of alcohol or driving while intoxicated. That is down from the 249 arrests on the same charges made during that period in 2014, according to D.C. police. A police spokeswoman did not comment on possible reasons for the decrease, but said, “Of course we would want as many instruments as possible to reduce processing time by officers.”

A spokesman for the Office of the Attorney General, which prosecutes most drunken-driving cases in the city, called the impact minimal, saying authorities have relied on witness testimony or results of the blood or urine tests “to ensure we had the evidence required to prosecute DUI cases fully.” The office did not provide information on whether prosecution or conviction rates dipped for arrests made this summer.

Police labor union leaders said officers are choosing to charge many suspects with driving while impaired, which relies more on observation, rather than with the more serious charges of driving under the influence of alcohol or driving while intoxicated, which often require precise measurements of how much alcohol a person had consumed.

“It’s not worth the effort battling it in court if it all gets thrown out for something we have no control over,” Fetting said.

Problems with the breath machines are just one of the issues involving evidence that have impacted law enforcement agencies in the District this summer. A toxicology lab run by the Office of the Chief Medical Examiner halted some blood and urine testing for a few weeks.

A separate city-run DNA lab stopped work in April after a national accreditation board identified problems with analysis. Cases were sent to a private lab. Several top employees at the city lab, which is run by the Department of Forensic Sciences, were replaced. The lab is hoping to resume testing by November or December, spokeswoman LaShon Beamon said.

Authorities and defense attorneys said no criminal convictions have been impacted thus far by the OCME lab issues. But coming on the heels of the DNA testing issue at the District’s $220 million Consolidated Forensic Laboratory, which opened in 2012 in Southwest Washington, the developments fed questions about the reliability of forensic evidence used by city police and prosecutors, as well as the competence of examiners.

“It doesn’t give you confidence that the evidence gathering in the city is in good shape,” said Betty Ballester, head of the D.C. Superior Court Trial Lawyers Association. “What is going on? What do you trust? It gives you pause, that’s for sure.”

The Office of the Attorney General informed defense attorneys and D.C. judges of the issues with the breath tests and toxicology at the end of August, according to letters obtained by The Washington Post. The legal community had previously been notified of the halt in DNA testing.

The medical examiner’s office stopped blood and urine testing at the toxicology lab between May 22 and July 31, outsourcing 108 cases at a cost to taxpayers of about $40,000. D.C. police said there were no delays in investigations during this period.

Roger A. Mitchell Jr., the District’s chief medical examiner, said work was suspended because some technicians did not understand when a quality-control feature on the lab instruments indicated that there probably was a problem with results in one drug case. A supervisor later noticed the issue.

Mitchell said no faulty test results were published or used, but officials decided that they needed to reeducate staff.

“We trained people better to ensure that an error would not get to the last step before the results would go out,” he said. “I wanted to make sure we shored up any errors that could be identified and corrected.”

Two months after problems in the toxicology lab surfaced, Mitchell said he suspended the alcohol breath program when the supervisor resigned. He said that additional employees are now trained to maintain the breath machines so that one departure won’t impact the program. “So if someone were to leave now, we won’t have that gap in service,” he said.

This is not the first time that the District has stopped using breath-testing machines. The program was halted in 2011 after more than 400 people were arrested based on unreliable test results. At the time, the city was using machines that had not been properly calibrated. They were replaced with the Intoximeters, which are made by another company.

The District paid out about $368,000 to settle 20 civil cases brought by drivers convicted using faulty test results. Fetting was one of three police officers who testified about the problems; they later claimed that the department retaliated against them, but courts refused to grant them whistleblower status.

In 2013, city officials gave control of the new breath-testing program to the medical examiner’s office.

Fetting said that with the machines offline, it is more difficult for officers to arrest suspected drunk drivers. He said that taking suspects to the 4th District — which has the only operational breath machine — on Georgia Avenue NW, one mile south of the Maryland line, can take hours.

Blood tests administered at clinics also take time, and urine samples, which can be taken in station houses, are unreliable. Tests on urine are often imprecise because they measure alcohol consumed hours earlier and no longer circulating in the bloodstream.