The gap between black and white patients in the use of "high-tech" cardiac procedures has been well documented in studies employing a wide range of data sources, including Medicare claims (Ayanian et al., 1993; Boutwell and Mitchell, 1993; Escarce et al., 1993; Goldberg et al., 1992; Udvarhelyi et al., 1992), State hospital discharge abstracts (Carlisle, Leake, and Shapiro, 1995; Wenneker and Epstein, 1989), and Department of Veterans Affairs records (Peterson et al., 1994; Whittle et al., 1993). Black patients are consistently less likely to receive cardiac catheterization, coronary artery bypass graft (CABG) surgery, and percutaneous transluminal coronary angioplasty (PTCA), compared with white patients.
These findings are particularly surprising among Medicare beneficiaries, given their comparable insurance coverage. However, Medicare beneficiaries are still liable for deductibles and copayments, amounts that may total over $1,000 for cardiac surgery. They are also liable for as much as 15 percent above the Medicare Fee Schedule (MFS) amount if they are treated by non-participating surgeons. Such bills may be particularly onerous for black Medicare beneficiaries, who are less likely to have supplemental coverage (either private medigap or Medicaid) (McBean, Warren, and Babish, 1994). While some studies have adjusted for Medicaid eligibility (Ayanian et al., 1993; Escarce et al., 1993), none have been able to adjust for private supplemental coverage or income. Furthermore, while State Medicaid programs cover deductibles and coinsurance for dual Medicare-Medicaid eligibles, they will not pay any balance bill amounts. Observed black-white differences in use thus may be partly due to differences in ability to pay.
While black-white differences in disease prevalence might explain differences in procedure use, the utilization differential has been found to persist, even when limited to patients with specific cardiac diagnoses such as AMI. Because there is little discretion in whether or not to admit patients with AMI, systematic differences in illness severity can be ruled out as a reason for black-white differences in procedure use. Over one-quarter (26 percent) of Medicare AMI patients die within 30 days of admission (Udvarhelyi et al., 1992), however, suggesting that some patients simply may not live long enough to undergo these cardiac procedures. Previous research has not taken into account survival time when modeling the probability of use for black and white Medicare patients.
This article seeks to examine the role of limited ability to pay in explaining black-white treatment differences for AMI. In addition, we specifically adjust for the impact of differential mortality on the probability of use.
DATA AND METHODS
As part of a larger study of the MFS, we had selected a sample of 2.7 million Medicare beneficiaries that oversampled those groups of beneficiaries believed to be particularly vulnerable to access barriers (Mitchell, 1994). These oversampled groups included black beneficiaries, the disabled, residents of physician shortage areas, and those living in poverty areas. The sample was restricted to Medicare beneficiaries continuously eligible in both Part A and Part B who were not enrolled in a health maintenance organization. From this larger sample, we used Medicare inpatient hospital claims (taken from the Medicare Provider Analysis and Review [MedPAR] files) to identify all patients admitted between January 1, 1992, and September 30, 1992, with a principal diagnosis of AMI (International Classification of Diseases, 9th Revision, Clinical Modification [ICD-9-CM] Code 410.x1). This yielded a sample size of 18,202 beneficiaries, including 2,658 black beneficiaries, considerably more than would have been selected with a simple random sample.(1) We then extracted all of their claims for a 90-day period beginning with the date of admission. Both ICD-9-CM procedure codes (from MedPAR claims) and Current Procedural Terminology, 4th Edition (CPT4) procedure codes (from Part B claims) were used to identify the three procedures of interest: cardiac catheterization with angiography, CABG surgery, and PTCA. The use of both PartA and Part B claims to identify these procedures helps ensure a more complete count of procedure use.
Sociodemographic characteristics, such as age, sex, race (white and black only), and geographic residence (ZIP Code), were obtained for all beneficiaries from the denominator file. No information was available …