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New coronavirus testing sites continue to open across the region — but getting tested still isn’t easy. People need a doctor’s referral and then have to pass the screening put in place by the hospital or clinic that’s doing the testing.

Showing up without a note from a physician or the local or state health department will not only result in disappointment, it may also delay or prevent testing for first responders, health workers and people at a high risk for death from the virus, medical authorities warn.

People being tested should also be aware that it takes about three to seven days to get results, which come from state-run or private laboratories. Thus, new cases announced on a Wednesday, for example, probably came from tests taken a week earlier.

If you do have a doctor’s note, here is the latest list of known sites in the region where coronavirus sample collection or testing is underway:

The District

Children’s National Hospital has testing for children only in a drive-up and walk-up facility on the campus of Trinity Washington University.

A referral from a pediatrician is required, and tests are done three days per week, depending on the weather. Joelle Simpson, medical director of emergency preparedness at Children’s, said that’s to avoid contamination of the samples in case of rain.

●A drive-through test site on the campus of United Medical Center, the city’s only public hospital, will open by late this week and will be able to test up to 300 patients per day, the District’s health department said.

Kaiser Permanente’s D.C. clinic, which is located near the Kaiser Permanente Capitol Hill Medical Center, offers drive-up and walk-up testing. The sites are open for testing from 9 a.m. to 5 p.m., seven days a week.

The site — as well as Kaiser sites in the suburbs (see below) — requires a doctor’s order and appointment for the test.

Unity Healthcare Center has also begun testing for coronavirus at their Minnesota Ave., Kenilworth Terrace and 14th Street NW locations. Patients should be ready to answer questions about their health and be screened before getting a test.

George Washington University Hospital in the District’s Foggy Bottom neighborhood is building a drive-through testing site at the request of the D.C. government. It’s not yet known when it will be in operation.

Patients will need a test order from their own health care provider. If a patient does not have a doctor, GW can set up a telemedicine visit with one of their providers. Patients then will be able to access the drive-through site either by contacting the city’s 311 call center or accessing a soon-to-launch website.

Virginia

Virginia Hospital Center in Arlington set up a temporary drive-through site at 1429 N. Quincy St.

The location collects samples from about 60 patients per day and sends them out for testing. It is by appointment only and requires doctor-provided covid-19 test referrals. The site is reserved for Arlington residents, employees or patients of the hospital’s medical staff.

Kaiser Permanente has drive-through testing locations for its members in Woodbridge and Tysons.

The sites are open for testing from 9 a.m. to 5 p.m., seven days a week, and require a doctor’s order and appointment.

Inova Health System set up three of its urgent-care centers at Dulles South, North Arlington and Tysons to screen all patients with symptoms connected to respiratory illnesses and provide drive-through sample collection for tests that have been ordered by physicians. All three clinics are open daily, from 8 a.m. to 8 p.m.

PM Pediatrics in Fairfax County has opened a drive-up coronavirus testing center at 11056 Lee Highway. Only pediatric patients who have been evaluated by a pediatric expert, either in person or via the firm’s app, are eligible for the test. The only other site where the 55-clinic company offers the test is in Wayne, Pa.

Maryland

Three coronavirus testing sites opened Monday at vehicle emissions sites in Glen Burnie in Anne Arundel County, Waldorf in Charles County and Bel Air in Harford County.

The sites were designed to “pull people away from” emergency rooms and doctors’ offices and provide an alternative site, said Fran Phillips, the state’s deputy secretary for public health services.

They are reserved for people with symptoms who are either a health-care worker, a first-responder, over 65 years old, live in group homes or are deemed “medically unstable” by their doctor. Only people who have an order from their doctor or have an appointment will be tested.

A screening site at FedEx Field in Prince George’s County, run by the Prince George’s County Health Department, will accept patients by appointment only. Those who normally go to hospitals or emergency rooms to receive primary health care should call the county health department at (301) 883-6627 if they believe they have been exposed to and are exhibiting symptoms associated with this virus.

Kaiser Permanente has testing sites for its members in Gaithersburg, Largo and South Baltimore, with the same hours and criteria as in Virginia.

●Adventist HealthCare Shady Grove Medical Center has coronavirus testing only for critically ill patients who are likely to need hospitalization, said spokeswoman Lydia Parris. The hospital has no community testing sites, she said.

●The National Guard last week set up a screening and testing location in the Washington Redskins stadium’s parking lot. Tests are available only by preregistration through a physician.

●Some MedStar Health centers, with multiple locations in the region, are testing for the virus. Patients are asked to call the clinic or hospital first.

Holy Cross hospitals, in Silver Spring and Germantown, have tents to triage patients with influenza-like illnesses, including the novel coronavirus.

Patients then may be tested in the emergency room, spokeswoman Kristin Feliciano said, but the hospitals are not set up to receive walk-in community members looking for tests. Anyone suspecting they have symptoms should first contact their primary-care provider, and should call the hospital before turning up there.

●Suburban Hospital in Bethesda, part of the Johns Hopkins network, offers testing for patients who do not need emergency care and who have been referred by their Johns Hopkins doctor specifically for covid-19 testing.

— The private health care provider Kelly Goodman NP & Associates is also doing drive-through testing at the Waldorf School in Bethesda, available Wednesdays and Fridays. Their Clarksville, Md., office will also offer drive-through testing on Friday. To schedule a test, call 202-684-7167.

This is a developing story. It will be updated as new information becomes available.

Kyle Swenson, Erin Cox, Darran Simon and Rebecca Tan contributed to this report.