Executive Health Resources is a firm hospital systems hire to fight back against insurers when they deny claims or pay bills for less than a hospital thinks it is owed. Executive Health was acquired in 2010 by UnitedHealth Group—insurance company UnitedHealthcare’s parent. “It does seem as though there is reason for concern because they can use our own information against us,” said Dennis Dahlen, CFO of Banner Health. United rivals have expanded their portfolios as well, said Thomas Carroll, a managed-care analyst for Stifel Nicolaus. Aetna bought Medicity, which builds information exchanges for doctors and hospitals to share patient data electronically, last year. “We’re in the beginning of a lot of these kinds of conflicts in historically stable relationships,” said Glenn Melnick, a health economist at the University of Southern California.