Medicaid and uninsured patients were consistently less likely to receive DES than were privately insured patients during 2003–2008, even after accounting for a range of patient and hospital characteristics. Medicare patients were also less likely to receive DES, though the gap with privately insured patients was smaller. The differences fluctuated over time as the popularity of DES relative to BMS rose and fell. They were large after DES approval, narrowed but were still present as DES use reached saturation, and increased again as DES use declined after safety concerns became widespread in the second half of 2006. By the end of 2008, as DES use climbed again, the gaps grew. Furthermore, variation in DES use by payer was attributable almost entirely to differential treatment within hospitals, and the within-hospital differences were larger in Q4 2008 than at any other time.
Our finding that payer differences in DES use principally reflected intra-hospital differences in treatment is consistent with evidence that hospitals appear to treat cardiovascular patients differently depending on the generosity of their insurance coverage.27–28
Further, payer differences in DES use did not stem from Medicaid and uninsured patients’ concentrating in hospitals with lower DES usage, ruling out a number of potential explanations and implying that policies aimed at redirecting patients to high-use hospitals would not have ameliorated these differences.18
Understanding the within-hospital between-payer differences in DES use depends critically on context-specific features. Importantly, physicians receive the same reimbursement for using DES as for BMS.8
This equality presumably eliminates their direct financial incentives, which have led to treatment differences in other contexts.29
Even after adjustment for other patient-level demographic and socioeconomic factors, payer type could nevertheless influence physicians’ perceptions of patients that in turn affect their choice of stent. One specific concern relates to patient adherence to long-term antiplatelet therapy after DES, which was magnified after the safety warnings in 2006.30–33
Physicians may have anticipated that Medicaid and uninsured patients were less likely than privately insured patients to adhere to clopidogrel, perhaps because of perceived or actual differences in patients’ out-of-pocket costs or other reasons.
It is also possible that the relationship between payer type and stent choice was shaped by hospitals’ financial incentives. Across a range of high-cost drugs and devices known as “physician preference items,” there is a well-known misalignment of incentives between physicians, who choose which drugs and devices to use, and hospitals, which bear the cost.34
Hospital acquisition prices for DES have been much higher than for BMS,35
resulting in lower or even negative hospital profit margins for DES for all payer types. Because the margins for DES were even lower relative to BMS for Medicaid and uninsured patients, hospitals may have effectively encouraged cardiologists to concentrate DES use among higher-paying patients, particularly during the early supply shortages.36
Although absent from our data, hospital managers have adopted a number of strategies to influence physicians’ device use, including value analysis teams34
Our analysis is limited in two important ways. First, the NIS does not include information on all factors, including clinical data, physicians might consider in selecting stents. As a result, our estimates might suffer from omitted variables bias, and we cannot reach a definitive conclusion about the causes of within-hospital variation in DES use by payer. Also, because the NIS data do not reliably identify physicians, we cannot determine whether the within-hospital differences were created by differences within or between cardiologists.
Second, we cannot say whether differences in DES use imply differences in quality of care. As our data do not identify on- vs. off-label use, we cannot distinguish whether differences reflect under-treatment for some payer types, over-treatment for others, or appropriate care in some or many instances. Given the importance of patient adherence with antiplatelet therapy, however, even with information on clinical appropriateness we could not determine whether a specific patient would have benefited more from DES or BMS. Reasonable physicians might select DES for one patient they thought was likely to adhere to clopidogrel, and select BMS for another patient deemed unlikely to adhere, even if the two patients were otherwise identical.
A broader issue is whether differences in the use of DES by payer type reflect a systemic health care disparity. This depends in part on establishing the incremental value of DES over BMS. Although the principal benefit of DES has been the reduction of restenosis risk, scientific understanding of their risks has evolved even as technology has improved. The value of DES depends on a number of variables and has changed over time, which may be why physicians’ perceptions of DES value vary greatly.
Whether our findings indicate a systemic disparity depends also on whether patients with generous insurance are better positioned to accrue the benefits of DES. As suggested by Goldman and Lakdawalla,38
new technologies are likely to exacerbate disparities when they are complicated to use, because more educated and wealthier patients are better able to manage the demands of a complicated treatment and thus will be selected disproportionately for it. Because DES requires a substantially longer regimen of clopidogrel than BMS, physicians may have limited DES to individuals they thought were more likely to adhere to that regimen, and they may have used payer type as a proxy for adherence. This would explain why the gaps in DES use by payer type grew largest at the end of 2008, as physicians responded to safety warnings and increasingly restricted DES to patients perceived as being clopidogrel-adherent. However, little is known about either the accuracy of clinicians' predictions of long-term medication adherence or whether social factors are reliable predictors of adherence. Data from one center indicate that clopidogrel adherence rates one year post-stent varied little by stent type or payer type.20
Regardless, differences in the use of innovative technologies based on socioeconomic factors like payer type are likely to occur whenever a technology requires physicians to reserve the treatment for patients they judge to have adequate abilities and resources.
During its initial diffusion period and since safety concerns came to light, access to an important new cardiovascular technology differed substantially by payer. Specifically, rates of DES use among the uninsured and Medicaid populations were well below privately insured patients. Although our understanding of the specific mechanisms at work is incomplete, these gaps are almost entirely attributable to differential treatment within hospitals and independent of between-hospital differences. While it does not necessarily follow that physicians based their use of DES directly on patients’ payer type, it is unlikely that Medicaid and uninsured patients were less likely than privately insured patients to be clinically appropriate candidates for DES. Thus, the observed differences in DES use across payers likely stemmed from differences in physicians’ judgments about patient adherence and/or concerns about hospital finances.