PITTSBURGH — The two largest hospital networks in Western Pennsylvania currently pay doctors based on the number of patients treated — but they want to add bonuses tied to quality.

UPMC and West Penn Allegheny Health System officials said that volume will remain a key part of the pay formula, but changing to a pay-for-performance model could help cut costs and reduce unnecessary treatments.

“You really need to compensate physicians based on the value they bring to the table,” said Dr. Tony Farah, chief medical officer at West Penn Allegheny. “We want our physicians to continue to be productive. We also want them to be engaged and incentivized to work toward great patient outcomes.”

Primary care physicians at UPMC will be able to receive up to a 20 percent bonus if they meet quality measures under a payment model being tested during the next year that officials hope will “better align incentives with providing the highest-quality and most cost-effective care,” according to Dr. Steven Shapiro, UPMC’s chief medical and scientific officer.

Farah said West Penn Allegheny, which pays doctors based on productivity, research and teaching activities, wants to include patient outcomes and quality, but that would not be instituted until after the completion of Highmark’s planned acquisition.

In a 2007-08 American Medical Association survey, nearly 80 percent of doctors said they did not participate in pay-for-performance programs. But the association says such programs can “serve as a positive force in our health care system” as long as they are patient-centered and evidence-based.