McGrath said all of the results for tests she had undergone had been negative. Mrs. Bush may be released later Tuesday or could be held overnight to watch her condition.
McGrath said former President George H.W. Bush was with her.
Mrs. Bush is 83.
The former Barbara Pierce, daughter of the publisher of McCall's magazine, married George H.W. Bush in January 1945 when he returned a hero from World War II.
She was the girl who, swept off her feet by a handsome Navy aviator, dropped out of college to marry him, "the first man I ever kissed," and thence was destined for a lifetime role as Supermom.
They had had their first child, George, while still at Yale in 1946. A daughter, Robin, died in 1953 of leukemia a few weeks before her 4th birthday. The other Bush children are sons Jeb, Neil and Marvin, and daughter Dorothy.
For years, Barbara Bush has been a sunny presence in American life, the sort of person who would make herself and others comfortable at your kitchen table. But she also was tough.
In the course of being George H.W. Bush's wife, she had to pack up and move the household 28 times before residing at 1600 Pennsylvania Avenue in Washington.
Mrs. Bush disclosed she was suffering from an overactive thyroid ailment known as Graves' disease when she lived at the White House. The disease causes teary eyes and double vision in Mrs. Bush, according to her doctors.