Many people who are unaware they’re living with HIV visit emergency rooms (ERs) for medical care. But a University of Cincinnati study found even ERs that have HIV testing programs were missing opportunities to test—in as many as 28 percent of patients.

Why? “It’s logistics,” says Michael Lyons, MD, the study leader. “Say you have 80,000 ER visits in a year. Doing anything 80,000 times in a place where [staff] are already overwhelmed is challenging.” Another reason: ERs may not have a 24/7 staffer dedicated to ensure every patient is offered an HIV rapid test, which gives results in 20 minutes. And, of course, some people don’t want to be tested.

Dan Wiener, MD, who heads the ER at New York City’s St. Luke’s-Roosevelt Hospital Center, says his ER offers oral-swab rapid testing to everyone who comes in—but many people decline the offer. That’s why, of the 7,000 people who use the ER and could get tested each month, only 2,000 take the test. “We’ve learned that acceptance rates [vary depending on how] different nurses offer the test, but we haven’t pinpointed yet what gets higher response rates,” he says.

Meanwhile, in Houston, Ben Taub General Hospital’s ER manages to HIV-test up to 50 percent of patients. They tell everyone who needs blood work that an HIV test will be added unless the patient declines. “We’ve had less than 1 percent refuse,” says ER head Shkelzen Hoxhaj, MD. Even fewer reject an oral-swab rapid test.

As long as ER workers are harried and some patients say no, it’s impossible to test 100 percent. The trick to more testing? “Places that have been successful,” Lyons says, “have had a champion in the ER who wanted to pursue testing and [pushed] the administration and staff.”