In an analysis of all-payor administrative data, we found evidence of improved outcomes in specialty hospitals for AMI but statistically similar outcomes for CABG. Our findings were consistent among Medicare and non-Medicare populations, when specialty hospitals were compared with general hospitals within the same market and within the same state, and when patients who required transfer to another acute care hospital were treated as adverse outcomes. The results of this study provide important validation of prior studies relying exclusively on Medicare data and confirm the results of prior studies.
A number of our findings merit further discussion. First, the finding that specialty hospitals appeared to have statistically significantly better outcomes for AMI but similar outcomes for CABG requires explanation in light of prior studies. Nallamothu and colleagues, using Medicare administrative data, found that 30-day AMI risk-adjusted mortality was a statistically significant 10 percent lower in specialty hospitals than general hospitals, mirroring results of the current study (Nallamothu et al. 2007
). Cram, Rosenthal, and Vaughan-Sarrazin (2005)
found that CABG mortality was a statistically significant 15 percent lower in specialty cardiac hospitals than in general hospitals. Using slightly different methods, the current study revealed a 33 percent relative reduction in in-hospital AMI mortality in specialty hospitals as compared with general hospitals (2.8 vs. 4.2 percent) and a 20 percent relative reduction in CABG mortality (1.6 vs. 2.0 percent). While the improved outcomes for specialty hospitals in the current study were statistically significant for AMI but not CABG in this analysis, we believe that the consistent advantage now observed among specialty hospitals should be acknowledged and is important for patients, physicians, and policy makers. Our findings extend the results of prior studies using an alternative data source that includes younger patients not insured by Medicare. We found that the advantage of specialty hospitals persisted when the comparison group of general hospitals was extended from those within the same HRR as the specialty hospitals to a broader group including all competing general hospitals within the state; this is a small but important expansion of prior studies, which exclusively compared outcomes of specialty hospitals with those of general hospitals located within the same health care markets.
In interpreting our results, it is important to consider our definitions of specialty hospitals and general hospitals. We identified specialty cardiac hospitals using a methodology that has been used previously both by government regulators and researchers—namely identifying physician-owned hospitals for whom an extremely high proportion of total admissions were cardiac in nature that do not provide general care including pediatric and obstetrical services (2003a
;). While this definition clearly identifies a well-circumscribed group of hospitals, there are potential shortcomings to defining hospital specialization in such a rigid manner. In reality, hospital specialization might best be viewed as a continuum measured as the proportion of a hospital's total admissions that fall within a given group of diseases rather than a dichotomous measure (Hwang et al. 2007
). There is growing concern that increasing competition between hospitals and tightening financial margins are encouraging many general hospitals to focus on better-reimbursed service lines including cardiac care, orthopedics, and oncology care with uncertain consequences (Pham et al. 2004
; Berenson, Bodenheimer, and Pham 2006
;). To be included in our study a cardiac hospital was required to have a unique billing number for purposes of reimbursement by payors. Thus, free standing cardiac hospitals located on large medical campuses as well as cardiac hospitals located with a larger general hospital were not considered specialty hospitals for purposes of our study.
Our definition of general hospitals also merits brief mention. We defined competing general hospitals as all general hospitals performing at least five PCI and CABG procedures per year. We excluded general hospitals that did not provide revascularization from our analysis. Since specialty cardiac hospitals, by definition, provide comprehensive revascularization services, it seems appropriate for our comparison to be limited to general hospitals providing a similar scope of service. Alternatively, by eliminating general hospitals that do not perform revascularization, we likely excluded the smallest (and highest mortality) general hospitals from our analysis; had these hospitals been included, it is likely that the in-hospital mortality advantage seen in specialty hospitals for AMI would have been even larger.
It is also important to consider the strengths and limitations of administrative data in general and the SID data more specifically. While there is a long history of using administrative data in assessing patient outcomes and quality of care (Hannan et al. 1997
; Iezzoni 1997
;), there are legitimate concerns about such a strategy, most notably using ICD-9-CM codes to measure clinical status. For example, ICD-9-CM codes may not capture laboratory values or physical findings that have prognostic value. There are also concerns about errors in ICD-9-CM coding using patients' medical records (Hsia et al. 1988
; Waterstraat, Barlow, and Newman 1990
;). Studies that have formally investigated the accuracy of ICD-9-CM codes have found varying levels of agreement between patient medical records and administrative data (Fisher et al. 1992
; Hannan et al. 1992
; Green and Wintfeld 1993
; Baron et al. 1994
). While agreement is generally excellent for major procedures, agreement may be poorer for some comorbid conditions, leading some to recommend caution when using administrative data to make inferences about quality of care or treatment outcomes. In a recent study Krumholz et al. (2006a
; examined the agreement between hospital quality for AMI and CHF assessed using MedPAR administrative data as compared with clinical data and determined that while clinical data is superior, administrative data provides essentially similar results. Nevertheless, improving administrative data is a priority, particularly through the inclusion of a present on admission (POA) indicator, which would distinguish conditions that are preexisting from those arise as complications arising during the hospital stay (Parker et al. 2006
; Glance et al. 2008
;). For example, Glance et al. (2008)
evaluated conditions defined by the Elixhauser algorithm and determined that paralysis and coagulopathy are misclassified >20 percent of the time as preexisting conditions when developing during the course of an AMI admission. Nevertheless, we generated additional analyses in which these variables were excluded as potential comorbid conditions, and conclusions were virtually identical.
There are a number of limitations to our study that merit brief mention. First, our study focused on patients admitted to specialty and general hospitals with AMI in four states; thus, generalizing our findings to all hospitals and diagnoses should be made with caution. Additional investigations are needed to further examine the consistency of these two administrative data sources. Second, our analyses were somewhat limited by the idiosyncrasies of the SID data. For example, the structure of the SID data differs significantly by state; some states report patient age as a continuous variable while others report age as a categorical variable to prevent patient identification. In addition, the SID data do not assign any unique patient identifiers, making it impossible to track patients over time to look at mortality occurring after discharge or tracking patient readmissions or transfers to other hospitals. Despite these limitations, the SID data offer a tremendous resource for answering questions that cannot be addressed with Medicare data alone.
In summary, our results provide further evidence that physician-owned specialty cardiac hospitals deliver modest improvements in patient outcomes as compared with general hospitals. Specialty cardiac hospitals may represent a good choice for patients seeking hospitals that deliver high-quality care.