The effect of managed care market share on appropriate use of coronary angiography among traditional Medicare beneficiaries.

Evidence suggests that when managed care market share increases in a geographic area, expenditures in Medicare's fee-for-service sector decrease. But it is unclear how expenditure reductions relate to the quality of medical care for traditional Medicare beneficiaries. We estimated how managed care market share varied with the proportion of fee-for-service Medicare beneficiaries who were admitted for acute myocardial infarction (AMI) and underwent angiography. We classified patients as appropriate, discretionary, and inappropriate, according to guidelines of the American College of Cardiology and the American Heart Association (ACC-AHA). Within all ACC-AHA classes, coronary angiography fell slightly as managed care market share increased.