A six-year federal investigation of DaVita Inc. has concluded without any charges being filed, the El Segundo-based dialysis center operator announced Tuesday. It was the oldest of three investigations into the company’s business practices.

DaVita said that government officials told them the investigation into its business practices was over. The company, one of the nation’s largest dialysis center operators, was among several similar businesses investigated, with some paying billions of dollars in fines and settlements. The industry was accused of favoring some drugs over others and using tests that would more easily justify certain add-on treatments.

The investigation began sometime before February 2001, when the company was notified by the civil division of the U.S. Attorney’s Office for the Eastern District of Pennsylvania. DaVita received a formal subpoena in May 2002. Investigations in two other jurisdictions are pending, a company spokeswoman said.

“We are pleased that the government, after a lengthy and thorough review, has decided to close this broad investigation into our business practices,” Chief Executive Kent Thiry said in a statement. “We are proud of our culture of regulatory compliance at DaVita.”

DaVita shares closed up $1.19, or 2 percent, to $53.56 on Tuesday. The company operates 1,300 outpatient dialysis facilities in 42 states and Washington D.C.