In an attempt to remove itself from liability for a patient's death, the University of Pittsburgh Medical Center claimed in a court filing this week that it doesn't run hospitals or employ any health care professionals.

The family of Rose Lee Diggs, an 89-year-old Homewood woman who wandered from her room and died on the roof of UPMC Montefiore in December, sued the health system claiming its negligence caused the woman's death.

Mrs. Diggs went missing from her 12th-floor room Dec. 2 and was found dead the next morning on the roof one floor above, wearing only a hospital gown and slippers after a night in which temperatures dipped into the 20s.

Defendants UPMC and UPMC Presbyterian Shadyside -- which includes the Montefiore campus -- filed full answers to the Diggs complaint Tuesday denying any negligence. UPMC took the position that even if there was wrongdoing on the part of Montefiore employees, it's not the health system's responsibility.

"Each of the hospitals and health care facilities are independent not-for-profit corporations that are directly responsible for their operational functions," wrote UPMC attorneys John C. Conti, Howard A. Chajson and Lisa D. Dauer.

UPMC spokesman Paul Wood wrote in an e-mail that it is the health system's legal opinion that only the individual hospitals can be sued, not the "holding company" of UPMC.

The response by UPMC Presbyterian Shadyside, authored by the same three attorneys, attacked the specific claims.

The filing states that a fire exit door leading to the roof that Mrs. Diggs appears to have used was not required to be alarmed. Also, the attorneys wrote, hospital staff did not discover a broken lock on a door to mechanical areas on the 13th floor until after Mrs. Diggs' death.

In addition, the response denies claims that hospital staff delayed in alerting police that Mrs. Diggs was missing or tried to remove evidence from the scene before authorities could investigate.

The suit was filed by Mrs. Diggs' son, Roderick. His attorney, Robert N. Peirce III, declined comment yesterday.

UPMC's answers come on the heels of last month's ruling by Common Pleas Judge R. Stanton Wettick Jr. that threw out many of the lawsuit's claims, which he determined to be irrelevant to the case. Among other passages, the judge struck references to other patients wandering from their rooms and a critical report by the state Department of Health regarding the Oakland hospital.

Also last month, Allegheny County District Attorney Stephen A. Zappala Jr. said his office would not file criminal charges in Mrs. Diggs' death.