Previous large-scale population-based reports have identified several patient and system attributes, such as race, insurance status and day of admission, associated with adverse outcomes of hospitalization for various medical conditions. For example, AA patients are at increased risk of in-hospital mortality following hepatectomy and cholecystectomy 
. Medicaid patients are at increased risk of postoperative complications and mortality following colorectal surgery 
. Finally, weekend admission for acute upper-gastrointestinal bleed 
and stroke 
are associated with increased mortality relative to weekday admission. To our knowledge, the effect of these parameters on outcomes of patients admitted with cholangitis has never been assessed. Based on these considerations, we examined the effect of several important variables on in-hospital mortality, prolonged LOS and increased HC in a large contemporary (1998–2009) population-based cohort of individuals admitted with ascending cholangitis.
Our results demonstrated several important points. First, we identified key differences in treatment delivery between patients who died and those who did not. Indeed, lower rates of ERCP and cholecystectomy were recorded in patients who died during hospitalization. Conversely, these patients experienced higher rates of percutaneous and surgical drainage. The Tokyo 2007 guidelines recommend ERCP as the standard of care for drainage when possible 
. These findings may suggest that this subset of patients may have been were sicker at presentation, perhaps preventing them from undergoing a timely ERCP 
. Moreover, the overall rate of biliary drainage is lower that expected, likely because the NIS only contains data on procedures performed during admission and does not account for elective interventions.
Second, our results indicate that on average, worse outcomes, including in-hospital mortality, prolonged LOS and increased HC apply to AA, Hispanic and API patients admitted with cholangitis. Several hypotheses may be proposed to explain our findings. Indeed, it is possible that AA, Hispanic and API patients present late with more severe disease and therefore worsening outcomes. Previous reports have documented racial differences in stage and severity of disease at presentation 
. Second, anatomical or biological differences may explain the disparities. For example, Asians are at increased risk of bile duct injury during cholecystectomy 
, purportedly due to a higher degree of anatomical variations. It is also possible that, when all confounders are accounted for, AA, Hispanics and API do not receive the same level of care as their Caucasian counterparts as has been suggested previously 
. It is possible that barriers, including language barriers 
, contribute to racial disparities. Furthermore, it is possible that disparities in access to ERCP may be responsible for the variation in outcomes. While we did find differences in ERCP rates across the racial groups, in two of three cases they were significantly higher than for Caucasians and therefore not likely to have been a major factor in explaining the mortality differences. Finally, it has been suggested by some that a wide range of patient-physician relationship issues may also in part explain the observed disparities 
Furthermore, our study also shows that Medicaid and Medicare patients are at increased risk of in-hospital mortality, prolonged LOS and increased hospital charges compared to their privately insured counterparts. Several hypotheses may be postulated to explain the discrepancy. Medicaid and Medicare patients may present with later stage of disease, as reported in other conditions 
. Poor access to health care may also be at cause 
. In addition, the difference in outcomes may also be due to unaccounted socioeconomic differences, as median zip code income does not entirely approximate socioeconomic status. Finally, subset analyses demonstrate that the effect of Medicare coverage on adverse outcomes is more pronounced in patients younger than 65 years of age, suggesting the presence of unmeasured confounders, since Medicare eligibility under 65 is restricted to individuals with long-term disabilities or those diagnosed with specific diseases. It is also possible that the difference observed in Medicare patients 65 and above may be overstated. Indeed, in future studies, Medicare patients younger than 65 years of age might be used as a marker of comorbidities, in addition to CCI.
In this study, weekend admission was associated with a decreased risk of in-hospital mortality and increased hospital charges. These findings contrast with previous studies reporting worse outcomes in patients admitted during the weekend 
, presumably due to a lack of resources and staffing on weekends. Yet, it is possible that weekend patients may receive more prompt attention from the medical team, who might not have been readily available during regular work hours, as has been suggested for other conditions. 
Indeed, Carr et al
. observed similar findings in the trauma population where weekend admission was associated with decreased mortality 
. Similarly, Luyt et al.
observed a reduction in the mortality of patients in the intensive care unit during off hours 
Finally, several patient and hospital characteristics were also associated with worse outcomes. These include increasing age and CCI. Indeed, we corroborate previous reports that these two attributes were associated with higher in-hospital mortality 
, prolonged LOS and high HC 
. Biliary obstruction due to neoplasm was also associated with worse outcomes relative to choledocholithiasis, as also previously reported 
. Conversely, higher socio-economic status was associated with shorter LOS, which was also recorder in a population-based study from Belgium 
. Patients treated at urban and teaching hospitals were at increased risk of in-hospital mortality, prolonged LOS and increased HC, as seen in other conditions 
. Higher in-hospital mortality recorded at high-volume, urban and/or teaching institutions may be due to differences in referral and transfer patterns, consequently case-mix. For example, data from the Washington State Commission Hospital Abstract Reporting System has shown that longer travel distance is associated with more resources and higher hospital charges 
. Finally, the association between in-hospital mortality and geographic variation does not follow other reports, as northeastern location was associated with poorer outcomes in our analysis. Explanatory factors for this discrepancy are unclear and may relate to unadjusted confounding, unrecognized biological factors or a type I error.
Limitations include the study design; indeed, observational studies cannot be used as proof of a causal relationship. Some reasons for this are the inability to adjust for important patient variables such as disease characteristics, personal preferences, education, and disease severity. Unavailability of individual gastroenterologist, surgeon, and interventional radiologist volume represents another limitation, which is shared by several other analyses 
. It is also possible that the true mortality is underestimated as some patients may have died at other institutions where their mortality was not captured. Moreover, the accuracy of administrative ICD-9-CM claims for identification of cholangitis and ERCP has never been validated within the NIS, which could lead to some degree of misclassification. Finally, since our analyses are based on a relatively large dataset, it is important to noteworthy that some of our results might be statistically significant, but of low clinical yield. Nonetheless, most of the differences discussed in the current manuscript have important health policy and clinical implications.
To summarize, in patients presenting with cholangitis, race and insurance status represent independent predictors of in-hospital mortality. Specifically, AA, Hispanic, API patients presenting with cholangitis are at increased risk of in-hospital mortality, prolonged LOS and high hospital charges, relative to their Caucasian counterparts. Moreover, Medicaid and Medicare patients are also at increased risk of in-hospital mortality, prolonged LOS and high hospital charges, relative to privately insured patients. Whether these disparities are due to biological predisposition or unequal quality of care require further investigation.