(CNN) — Secretary of State Hillary Clinton remained hospitalized on Monday for a blood clot that was discovered during a follow-up exam related to a concussion she suffered this month, her spokesman said.
She was admitted on Sunday and 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.”
She was scheduled to return to work at the State Department this week after being sidelined for most of the past month.
Her illness forced her to bow out of testifying on December 20 before the House Foreign Affairs Committee on the deadly September attack on the U.S. diplomatic compound in Benghazi, Libya.
Clinton plans to step down once a replacement is confirmed by the Senate. President Barack Obama has nominated Sen. John Kerry.