The effect of office visit copayments on preventive care services in an HMO.

We examined the impact of a $5 office visit copayment on use of preventive care services by Washington State enrollees in a health maintenance organization. Utilization data were compared for 30,415 State enrollees and 21,633 enrollees without copayments who were enrolled 12 months before and after the start of copayments. Copayments resulted in a 14% decrease in physical examinations but did not significantly affect immunization rates for young children, cancer screening tests received by women, or medication use by persons with cardiovascular disease. For employed populations small copayments appear to have little impact on the most valuable types of preventive care services.