Coronavirus tests taken at an assisted-living facility in Chevy Chase were processed at a lab that was shut down by the Maryland Department of Health for not having the right certification to do the testing.

State health officials had previously disclosed that the Greenbelt lab, Advanced Pain Medicine Institute (APMI), handled samples collected from three pop-up clinics at churches last month.

But in a letter to residents and their families this week, the administrator of Brighton Gardens, an assisted-living facility run by the company Sunrise Senior Living, said some of its tests had also gone to APMI.

What’s not clear is how the facility’s samples ended up at APMI.

In her letter, the Brighton Gardens administrator described the situation as being the result of a contract between another lab, named CIAN Diagnostics, and APMI. But Sam Mullapudi, a principal at CIAN, denied having any business relationship with Brighton Gardens and said that he now suspects his two salesmen of sending work to APMI without his knowledge.

Matthew Dowd, a lawyer for the salesmen, said his clients dispute both Sunrise’s and CIAN’s accounts but declined to say how. He also said that they were unaware of the issues with APMI until they became public.

Ebony Wilder, a spokeswoman for the Maryland Health Department, said officials are trying to understand the situation.

“The Maryland Department of Health is continuing to investigate APMI’s performance of COVID testing, the relationship, if any, between APMI and CIAN, and APMI’s and CIAN’s compliance with applicable federal and state laws,” Wilder said in an email.

Nursing homes have been especially hard hit during the pandemic. In late March, Montgomery County reported that three residents at a second Brighton Gardens facility in North Bethesda contracted covid-19, the disease caused by the virus. The residents — two men in their 80s and one man in his 60s — were hospitalized.

The state has made controlling the disease at facilities for the elderly a particular priority. And as part of that effort, CIAN holds a contract with the state to do coronavirus testing.

In a statement, Sunrise said it had now selected a new provider for its coronavirus testing.

“Upon learning of the Maryland Department of Health’s concerns regarding APMI, we took prompt action to address the situation,” the company said. “We’ve ceased working with APMI and any associated individuals, and promptly selected a new credentialed vendor to conduct testing going forward.”

The Health Department issued an order shutting down APMI’s coronavirus testing operation Saturday, saying the lab did not have the correct certification to be processing the tests. In a separate letter suspending the lab’s permit, officials wrote that it had begun the testing without the knowledge and approval of its own director.

The Health Department says APMI’s test results are unreliable and has urged people who received them to consider getting retested.

Reza Ghorbani, the president and medical director of APMI, did not respond to text messages and a voice mail asking about what work he did for Brighton Gardens, what relationship he might have with CIAN or whether he had an arrangement with its salesmen.

A website for APMI’s lab that previously advertised coronavirus testing now carries the following notice at the top:

“At this time, APMI is not certified to provide COVID-19 specimen collection or conduct laboratory analysis of COVID-19 specimens,” the notice reads. “Patients previously tested for COVID-19 by the APMI lab should consider alternative testing or re-testing.”

On Monday, Nancy Reburn, the administrator of Brighton Gardens, sent a letter to residents and their families.

“Today we were made aware that the company who performed some testing at our community in the past, Advanced Pain Medicine Institute (APMI), is no longer certified to provide COVID-19 testing and that prior results conducted by APMI may have been invalid, according to the Maryland Department of Health,” the letter said.

“We are taking this seriously and have been in contact with the lab company, Cian Dx, that contracted this work to APMI.”

Jay Gonchigar, a former owner of CIAN who continues to volunteer there, spoke on behalf of the lab in a phone interview Thursday in which Mullapudi was also on the line. Mullapudi was contacted by the state Monday asking about the link with APMI, Gonchigar said. Mullapudi told the state that his lab did not subcontract any coronavirus testing work and had no relationship with APMI, Gonchigar said.

On Tuesday, Gonchigar said he and Mullapudi confronted CIAN’s two salesmen by phone to ask whether they had turned any work over to APMI.

“They were asked point blank ’Did you ever send any samples in the name of CIAN to APMI?’ ” Gonchigar said. “They wouldn’t confirm it. They wouldn’t deny it.”

Dowd, the men’s lawyer, said “they are deeply concerned about the misrepresentations being made.”

“At all times,” his clients “were operating with one interest in mind: to ensure rapid and accurate COVID-19 testing for individuals in the DC area,” Dowd said in an email. “At no time” were they “ever aware of the alleged improprieties associated with APMI, prior to what has been reported in the news.”

A spokeswoman for Sunrise declined to answer questions about who Brighton Gardens dealt with in connection with the testing that was processed by APMI. She also did not respond to questions about how many people might have been affected or whether samples from other facilities run by the company went to APMI.

When it shut down APMI’s operation Saturday, the state said the lab had gathered samples at three pop-up clinics held at churches in Baltimore and Anne Arundel County. The facility was about to hold a fourth at a church in Howard County when the state’s order was issued.

Ghorbani, who was educated at Tufts University and practiced in the Boston area before moving to the Washington region in 2007, said in an interview Sunday that he saw an opportunity to use his lab to help the community and expand the reach of testing for the virus. The church events were held in conjunction with Maryland’s Korean community and catered in particular to immigrants and minorities.

Court records indicate that Ghorbani and his clinic have had legal and financial problems in recent years. Maryland has an open $34,191 lien against APMI for unpaid taxes.

The clinic also is involved in a long-running dispute with Amerigroup, a provider of Medicaid coverage in Maryland. The clinic sued Amerigroup in September, accusing it of failing to pay claims. But in its own lawsuit filed in November, Amerigroup alleged that APMI had overbilled to the tune of $298,830.81, claiming one kind of drug test as another one that paid better.

The Medicaid provider alleged that the kind of test the clinic was billing for was one that it did not have the correct certification to conduct. The lawsuits are still pending.

A phone message left with the firm that represented Ghorbani in the suits was not returned.