Hillary Clinton under close watch after suffering blood clot from fall

Ms Clinton’s doctors discovered the clot on Sunday, while performing a follow-up examination, her spokesman, Philippe Reines, said.

He would not elaborate on the location of the clot but said Ms Clinton was being treated with anti-coagulants and would remain at New York-Presbyterian Hospital for at least the next 48 hours so doctors can monitor her medication.

Mr Reines said: “Her doctors will continue to assess her condition, including other issues associated with her concussion. They will determine if any further action is required.”

The US secretary of state fell and suffered a concussion while at home in mid-December as she recovered from a stomach virus that left her severely dehydrated.

The concussion was diagnosed on 13 December and Ms Clinton, 65, was forced to cancel a trip to North Africa and the Middle East that had been planned for the next week.

The former First Lady and senator, who had planned to step down as America’s top diplomat in January, is known for her gruelling travel schedule. She is the most travelled secretary of state in history, having visited 112 countries while in the job.

Ms Clinton is considered a front-runner for the Democratic presidential nomination in 2016, although she has not announced plans to run.

Any serious medical concern could throw a fresh question mark over her future plans, although she has frequently alluded to her general good health.

The seriousness of a blood clot “depends on where it is,” said Dr Gholam Motamedi, a neurologist, at Georgetown University Medical Center.

Clots in the legs are a common risk after someone has been bedridden, as Ms Clinton may have been for a time after her concussion.

Those are “no big deal” and are treated with six months of blood thinners to allow them to dissolve on their own and to prevent further clots from forming, Dr Motamedi said.

A clot in a lung or the brain is more serious. Lung clots, called pulmonary embolisms, can be deadly, and a clot in the brain can cause a stroke, he said.

Keeping Ms Clinton in hospital could allow doctors to perform more tests to determine why the clot formed, and to rule out a heart problem or other condition that may have led to it, he said.

Ms Clinton was forced to cancel a 20 December appearance before Congress about a scathing report into the 11 September attack on the US diplomatic mission in Benghazi, Libya, that killed ambassador Chris Stevens and three other Americans. The report found that serious failures of leadership and management in two state department bureaus were to blame for insufficient security at the facility.

Ms Clinton took responsibility for the incident before the report was released, but she was not blamed.