Sen. Robert Byrd (D-W.Va.), 91, was admitted to an undisclosed hospital for observation Tuesday after falling at his home in Northern Virginia.

Byrd, the Senate’s longest-serving Member, was taken to the hospital “as a precautionary measure,— according to a statement from his office. He is expected to remain at the facility for a few days for monitoring and antibiotic treatment.

“While having no broken bones or bruises, upon examination, doctors found an elevated white-blood cell count which can be an early sign of an infection,— the statement from Byrd’s office said.

Byrd, who also serves as the President Pro Tem, has been in declining health in recent years. For more than six weeks this spring, Byrd had been hospitalized with infections.

On Tuesday, Senate Majority Leader Harry Reid (D-Nev.), who had not spoken to Byrd since his fall, told reporters, “We understand it’s nothing serious.—

Byrd’s attendance in the Senate has been somewhat spotty in recent months. On Sept. 10, he went to the floor to deliver a tearful tribute to the late Sen. Edward Kennedy (D-Mass.), with whom he served for close to five decades. Byrd was on the floor a week later to vote for an Obama judicial nominee and an amendment to the Interior and environment appropriations bill.

With Byrd’s absence and the death of Kennedy, Democrats are weighing the challenges of averting a filibuster. Majority Whip Dick Durbin (D-Ill.) said Byrd’s absence, which comes as the Senate is poised to consider a major overhaul of health care, is felt throughout the Democratic caucus.

“How do you calculate the absence of someone like Sen. Byrd? He’s been able to rally and come to the Senate for critical votes, and I’m sure he’ll do it again,— Durbin said.