Former United States Secretary of State Hillary Clinton
(CNN) -- Secretary of State Hillary Clinton was hospitalized Sunday after doctors discovered a blood clot during a follow-up exam related to a concussion she suffered this month, her spokesman said.
She is expected to remain at New York Presbyterian Hospital for the next 48 hours so doctors can monitor her condition and treat her with anticoagulants, said Philippe Reines, deputy assistant secretary of state.
"Her doctors will continue to assess her condition, including other issues associated with her concussion," Reines said. "They will determine if any further action is required."
Reines did not specify where the clot was discovered.
Clinton, 65, was suffering from a stomach virus earlier this month when she fainted because of dehydration, causing the concussion.
Blood clots "are clumps that occur when blood hardens from a liquid to a solid," according to the National Institutes for Health.
Clots can form inside veins or arteries or even the heart, the NIH says. "A blockage in the vein will usually cause fluid buildup and swelling," the NIH website says. Among the possible threats: Sometimes, a "clot can break loose and travel from one location in the body to another."
Sometimes, it can "partly or completely block" blood flow in a blood vessel. If a clot blocks an artery, it may "prevent oxygen from reaching the tissues in that area," the NIH says.
If not "treated promptly, it can lead to tissue damage or death."
Dr. Sanjay Gupta, CNN chief medical correspondent, says the fact that Clinton's clot is being treated with anticoagulants may offer a clue to the clot's location.
Anticoagulants are drugs that prevent clots from forming in the heart veins and arteries, according to the American Heart Association. Anticoagulants also prevent clots from growing larger.
"I think it's very unlikely this is a blood clot on top of the brain or around the brain specifically, because you just don't treat blood clots on the brain that way," Gupta said. "That would worsen the bleeding."
Clinton spent the holidays with her family last week after working from home.
She was scheduled to return to work at the State Department this week after being sidelined for the past three weeks. Her illness forced her to bow out of testifying on December 20 before the House Foreign Affairs Committee on the deadly attack on the U.S. Consulate in Benghazi, Libya. Deputies Thomas Nides and Bill Burns appeared in her place.
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The medical setback comes as Clinton is wrapping up her busy tenure as secretary of state, during which she has logged more than 400 travel days and nearly a million miles. She plans to step down from the post if and when Sen. John Kerry -- President Barack Obama's choice to replace her -- is confirmed by the Senate.
Elise Labott, CNN