The 50-something man with a shaved head and brown eyes was unresponsive when the paramedics wheeled him into the emergency room. He had no wallet, no cellphone, no distinguishing scars or tattoos. Almost two years after he suffered a devastating brain injury, no one had come looking for him. The man died, still a John Doe.

Hospital staff sometimes must play detective when an unidentified patient arrives for care. Establishing identity helps avoid treatment risks and can help find next of kin to help make medical decisions.

But federal privacy laws can make identifying a patient challenging at hospitals nationwide.

Social workers pick through bags and clothing, scroll through cellphones that are not password-protected, and scour receipts or crumpled pieces of paper for any trace of an identity. They make note of any tattoos and piercings, and even try to track down dental records. It's more difficult to check fingerprints, because that's done through law enforcement, which will get involved only if the case has a criminal aspect, said Jan Crary, supervising clinical social worker at L.A. County-USC Medical Center in Southern California.

Other hospitals resort to similar tactics. In Nevada, hospitals have an electronic system that assigns unidentified patients a "trauma alias," said Christopher Lake, an executive director at the Nevada Hospital Association.

And hospitals continue to face new challenges, such as the deadly mass shooting at a Las Vegas concert in October 2017. Instead of carrying a wallet, many concertgoers wore wristbands with scannable chips that contained their names and credit card numbers. More than 800 people were rushed to hospitals, none of which were equipped with the devices to scan the wristbands.

In 2016, a man with Alzheimer's disease was admitted to a New York hospital and assigned the name "Trauma XXX." Police and relatives inquired about him at the hospital several times but were told he was not there. After a week — during which hundreds of people searched for the man — a doctor saw a news story about him and realized he was the unidentified patient. Hospital officials later told the man's son that the mix-up happened because he had not explicitly asked for "Trauma XXX."

At the Southern California hospital, most John or Jane Does either regain consciousness or friends or relatives call about them, Crary said. Still, the hospital does not always succeed. From 2016 to 2018, 10 John and Jane Does remained unidentified.