Potential effects of managed care on specialty practice at a university medical center. 
The growth of managed care presents a challenge to academic medical centers, because the demand for the services of specialists is likely to continue decreasing.  We estimated the number of enrollees the University of Michigan Medical Center would need in its health maintenance organization (HMO) system in order to provide revenue equivalent to the total revenue it received for professional specialty care in 1992.  Rates of utilization and payment were based on the medical center's experience with managed care in 1992 in its independent practice association HMO, in which 25,000 members had capitated coverage and received primary and all specialty care from university physicians, and 15,000 members received primary care and most specialty care from physicians outside the university.  We assumed that persons not enrolled in Medicare were all enrolled in managed-care plans.  Primary care activity was excluded from the calculations of expense, revenue, and numbers of faculty members.  If all specialty services were provided by the university to HMO members, all the 21 specialties examined except obstetrics and gynecology and emergency services would require an enrollment of more than 250,000 to support the 1992 level of professional revenue and maintain the number of faculty members.  If university services were provided only for referrals from a loosely affiliated network of community physicians in the HMO system, all the 19 specialties examined except plastic surgery would require an HMO enrollment of more than 1 million.  In a combined model in which all specialty services were provided to 100,000 HMO members and network referrals were provided to 500,000 members, substantial changes in faculty composition would be needed in all the departments studied.  Because of the large number of HMO members required, unless other changes occur, it is unrealistic to expect that the University of Michigan Medical Center could create an HMO or network large enough to support the specialty practice of the current number of faculty members at the 1992 level of financing.