Former President George H.W. Bush drove her to Methodist Hospital where she was admitted Saturday morning. A spokeswoman for the Bush family told Houston's KTRK-TV Barbara Bush hadn't been feeling well for about a week.
The TV station said officials are calling the tests routine but haven't disclosed what they are for.
A year ago, Bush had aortic valve replacement surgery and in late 2008 she had surgery for a perforated ulcer.
Bush family spokesman Jim McGrath said the former first lady should be released within a couple of days.