Patients covered by Aetna, HealthAmerica and other insurance companies that provide full access to Mercy Hospital -- but not to UPMC Presbyterian and UPMC Shadyside -- are wondering what a UPMC-Mercy merger will mean for their access to the county's only Catholic hospital.

In the short term, the answer is: Nothing.

Mercy's existing contracts with health insurers will remain in place should the proposed merger announced last week come to fruition, hospital officials say.

Longer term, however, the access that UPMC provides to Mercy could be an important issue for health plans that traditionally haven't had contracts with UPMC's largest urban medical centers, relying instead on Mercy, Allegheny General and West Penn hospitals for advanced or "tertiary" hospital services.

Currently, Highmark and UPMC Health Plan subscribers have full access to UPMC Presbyterian and UPMC Shadyside; other insurers have failed to negotiate what they view as competitive contracts with the two medical centers, keeping them out of their provider networks.

"The loss of an independent Mercy'' for competing health plans potentially could have some impact " on their ability to provide an attractive hospital network," said David Lagnese, a consultant with benefits consultant Towers Perrin. "However, it would probably take some time to play out."

That's because companies such as Aetna typically have contracts with some of UPMC's hospitals, particularly those in the suburbs.

Benefit consultants say that one of the advantages Highmark has had in the local market is its ability to provide subscribers with access to all hospitals in the region. But Sam Marshall, president of the Insurance Federation of Pennsylvania, a lobby for the for-profit health insurers, said he didn't know enough about the particulars to speculate on what a UPMC-Mercy merger might mean for the competitive dynamic among insurers here.

"I think that the state and the general public have to evaluate any merger -- whether of hospitals or insurance companies -- in terms of will it create greater efficiency, will it create a monopoly that jeopardizes the benefits of competition and will it strengthen the fiscal soundness of the organizations," Mr. Marshall said.

It's also unclear what the proposed merger would mean for health care costs, said Mr. Lagnese, the benefit consultant. While UPMC certainly would get bigger with the merger, there is evidence that too much competition can boost costs as hospitals duplicate one another's services, he said.

"What I hear from my clients is that a two-system health care system [comprised of UPMC and the West Penn Allegheny Health System] in Pittsburgh would be fairly healthy," he said.

West Penn Allegheny officials immediately cried foul last week, saying that the proposed merger threatened to create a monopoly for UPMC. But Mr. Lagnese said that among his clients: "I haven't heard much alarm over this."