The purpose of this study was to evaluate the use of three invasive cardiovascular procedures –
coronary artery angiography, bypass graft surgery, and angioplasty – by residents of low, middle, and high socioeconomic status zip codes in California. The authors aimed to confirm the effect of socioeconomic status as a predictor of procedure use and to examine whether this effect was consistent across different health insurance categories. Data for this study included that California Hospital Discharge Data set and the 1990 census (for median household income). Subjects included California adult residents discharged from California hospitals between 1991 and 1993 with an ischemic heart disease diagnosis. African Americans, Asians, whites, and Hispanics were included.

Procedure use varied significantly by patients' socioeconomic status (SES) category. Overall, patients from high SES zip codes had significantly greater odds of having each procedure and those from low SES zip codes had significantly lower odds of receiving each procedure than those residing in the middle SES status zip codes. After stratifying by the five health insurance categories (private, HMO, Medicare, Medicaid, none), the effect of SES on the odds of receiving each procedure persisted. After adjusting for potential confounders, the effect of SES on the odds of receiving a procedure persisted for those with private insurance (bypass graft surgery, high SES only), no insurance, (angioplasty, low SES only), HMO (angiography; and bypass graft surgery, low SES only), Medicare insurance (angiography, high SES; bypass graft surgery, low SES, and angioplasty), and Medicaid (angiography, high SES; and angioplasty, high SES). These analyses are obviously limited by a lack of individual-level SES data and a lack of detailed clinical data.

The authors conclude that "increasing reliance on additional cost-sharing or HMO enrollment strategies may reduce unnecessary utilization, such strategies may not eliminate disparities in utilization by different SES status groups. Health system modifications must focus on elimination of SES status-related and other barriers to care in addition to reducing the overall cost of care."