On Friday, like a lot of people, Amber Gruner went to get a COVID-19 test at the free, walk-up, no appointment needed testing site at Judiciary Square.

“I had been out at the protests, saw that they had opened a bunch more testing sites, and [the D.C. government] was encouraging people to do it,” says Gruner, who waited in line for about an hour and a half. “So, I thought it was prudent to get tested.”

On Tuesday afternoon at 2:36 p.m., four days after taking the test, Gruner received a disconcerting email from the D.C. government. It read, in part:

“We regret to inform you that your test sample, taken at either the Judiciary Square or Anacostia testing site, was unable to be processed due to heat exposure.”

Gruner was ready for a positive or a negative test, but it hadn’t even occurred to her that there was another possibility.

“Obviously, you are waiting on this test and you are going to act differently based on whether it’s positive or negative. Well, I certainly didn’t expect this result,” she says. “There’s definitely some frustration.”

She wasn’t alone. The D.C. Department of Health confirmed to DCist on Tuesday evening that 407 testing samples taken last week at both Judiciary Square and Anacostia testing sites were rendered unusable because of heat exposure.

The temperature was regularly in the upper 80s in D.C. for most of last week. It’s not clear what exactly happened, though the city confirmed that the impacted tests were from Friday. They have not responded to questions on the specific cause of the heat exposure.

“We apologize for the inconvenience and are taking steps — such as the addition of more refrigeration at each testing site — to ensure the issue does not arise again,” a spokesperson for the D.C. Department of Health told DCist in an emailed statement.

Popville first reported that some residents had received emails alerting them about compromised tests.

Since the beginning of the month, D.C. has increased the number and availability of free, walk-up, no-appointment-needed coronavirus test sites in the city. This includes sites at Judiciary Square, Anacostia, UDC-CC Bertie Backus Campus, and ten firehouses. Mayor Muriel Bowser has encouraged all who protested in previous weeks to get tested.

But a number of these testing locations have been plagued by long lines and waits in recent days as the city attempts to keep up with the demand.

Besides walk-thru sites, there’s also appointment-only drive-thru sites and private health care options. And nonprofits like Community Organized Relief Efforts have offered their own free testing, including along protest routes this past weekend.

Despite the challenges, testing numbers in the District are rising. As of June 15, 67,126 people have been tested in D.C. This is an increase of more than 5,000 people since Thursday, June 11, and about a 13,500 person increase over the last ten days. (About a fifth of are non-D.C. residents, as testing remains limited to people with symptoms, or by appointment only, in most of the city’s suburbs.)

The city told those whose tests were compromised that they would be “pre-registered” for “priority placement in line” for retesting at the Judiciary Square location on June 17 and June 18 from 3 to 7 p.m.

Gruner plans on getting retested, but probably not through the options provided by the District.

“I’m going to call my doctor’s office and see if they are doing testing for those [who are] asymptomatic,” says Gruner. “I’m pre-registered, but so are the other people who this happened to. So, I don’t see how I’m going to avoid being in another two-hour line.”

This story was updated with confirmation that the impacted tests were from Friday.