Clinton was forced to cancel Dec. 20 testimony before Congress about a scathing report into the Sept. 11 attack on the U.S. 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. Clinton took responsibility for the incident before the report was released, but she was not blamed.
Some conservative commentators suggested Clinton was faking the seriousness of her illness and concussion to avoid testifying, although State Department officials vehemently denied that was the case.
Lawmakers at the hearings — including Sen. John Kerry, D-Mass., the Senate Foreign Relations Committee chairman who has been nominated by President Barack Obama to succeed Clinton — offered her their best wishes.
Last Thursday, before the discovery of the blood clot, Reines said Clinton was expected to return to work this week.
The former first lady and senator, who had always planned to step down as America's top diplomat in January, is known for her grueling travel schedule. She is the most traveled secretary of state in history, having visited 112 countries while in the job.
Clinton is considered a front-runner for the Democratic presidential nomination in 2016, although she has not announced plans to run.
AP Chief Medical Writer Marilynn Marchione in Milwaukee contributed to this report.