Gary Brooks Faulkner was also being questioned by a team of Pakistani investigators, two security officials said on condition of anonymity because they were not authorized to speak to media. They did not give additional details, including what the doctor had determined about the man's condition.
Catching the al Qaeda chief was 50-year-old Faulkner's passion, his brother Scott Faulkner said Tuesday. A devout Christian with a prison record, Faulkner has been to Pakistan at least six times, learned some of the local language, and even grew a long beard to blend in, relatives and acquaintances said.
"Our military has not been able to track Osama down yet. It's been 10 years," Scott Faulkner told reporters in Denver. "It's easier as a civilian, dressed in the local dress, to infiltrate the inside, the local people, gain their confidence and get information and intel that you couldn't get as an American soldier, Navy SEAL, whoever you might be."
Gary Faulkner, of Greeley, Colorado, arrived June 3 in the town of Bumburate. He was assigned a police guard, as is common for foreigners visiting remote parts of Pakistan. When he checked out of a hotel without informing the guard, officers began looking for him, senior police official Mumtaz Ahmad Khan said.
A police source told CBS News' Sami Yousafzai that Faulkner was arrested in a wooded area between the scenic Pakistani town of Chitral and the Taliban stronghold of Nuristan on the Afghan side of the border.
"We initially laughed when he told us that he wanted to kill Osama bin Laden," Khan said. But when officers found weapons, including a 40-inch sword and a pistol as well as night-vision equipment, "our suspicion grew."
He said Faulkner was trying to cross into the nearby Afghan region of Nuristan, one of several rumored hiding places for bin Laden along the rugged Afghan-Pakistan border.
Faulkner's sister, Deanna M. Faulkner of Grand Junction, Colorado, said her brother suffers from kidney disease that has left him with only 9 percent kidney function. "I'm worried about him. I'm worried that in Pakistan they won't give him his dialysis and if he doesn't get it, he's in serious trouble," she said.
U.S. Embassy spokesman Rick Snelsire said American officials were seeking consular access to a U.S. citizen in Pakistani custody and that once given, they could help arrange for medical care.
Gary Faulkner retained vivid memories of the Sept. 11, 2001, terrorist attacks and was serious but rational about his search, his brother Scott said. When Scott Faulkner dropped his brother off at Denver's airport May 30, the two discussed the possibility Faulkner would not return alive.
"He's as normal as you and I," Scott Faulkner said. "He's just very passionate."
Scott Faulkner said his brother sold all his tools to finance his trip and was prepared to die in Pakistan. He said Faulkner had a travel visa, obtained his weapons inside Pakistan and only took with him a Bible and plastic handcuffs.
Gary Faulkner, who was being questioned in the main northwest city of Peshawar, has not yet been charged with any crime in Pakistan. Khan noted police confiscated a small amount of hashish, enough for a single joint, from Faulkner.
The American was in and out of Colorado state prisons between 1981 and 1993, serving a total of about seven years in five separate stints for burglary, larceny and parole violations, state officials said.
Bin Laden, who is also reported to have kidney problems, has evaded a massive manhunt since Sept. 11, 2001, attacks on the United States, which he is accused of masterminding along with other attacks. The federal government has offered a bounty of $25 million for information leading to his capture.
Khan said when Faulkner was asked why he thought he could trace bin Laden, he replied, "God is with me, and I am confident I will be successful in killing him."