Clinton's illness in December abruptly halted her usually jam-packed schedule, forcing her to cancel a trip to North Africa and the Middle East and to postpone scheduled testimony before Congress on the fatal Sept. 11 attack on the U.S. diplomatic mission in Benghazi, Libya. "She is committed to testifying, and we are working with the committees on an appropriate set of dates," Nuland said.
She was also absent from the White House last month when Obama nominated Sen. John Kerry, D-Mass., to succeed her.
The State Department said Thursday that Kerry has started meeting with diplomatic staff to prepare for his Senate confirmation hearings, and while at the department's Foggy Bottom headquarters on Wednesday he received a large amount of briefing materials. Kerry will return to the State Department for regular meetings starting Friday.
Clinton's medical struggles have also raised questions about her political future and how her health might influence her decision about whether to run for president in 2016, a move prominent Democrats have been urging her to consider.
Patients with the particular type of clot Clinton has are typically on a blood thinner for three to six months and are monitored to see if the clot goes away, said Dr. Ralph Sacco, a neurologist at the University of Miami. Even if the clot does not fully dissolve, it can become stable and do no harm.
"Vein clots can come and go and sometimes not even cause symptoms," said Sacco who was not involved in Clinton's care. "A very high proportion of people have great recovery."
Clinton also suffered from a blood clot in 1998, midway through her husband's second term as president. That clot was located in her knee.
AP Chief Medical Writer Marilynn Marchione in Milwaukee contributed to this report.
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