Background:  The Affordable Care Act (ACA) has recently enabled millions of U.S. adults to acquire healthcare coverage.  The differential shift in payer mix in Medicaid-expansion versus non-expansion states after ACA implementation may be relevant to hospitals beyond reimbursement.  Medicaid has historically been associated with longer hospitalizations and higher mortality in diverse patient populations, more so than commercial insurance and often even uninsured payer status.  Currently, little is known about the impact of state Medicaid-expansion status on these outcomes nationally.  We sought to compare the following for general medicine patients at academic medical centers (AMCs) in Medicaid-expansion versus non-expansion states:  (1) payer mix trends and (2) length of stay (LOS) and in-hospital mortality both pre- and post-ACA implementation.

Methods:  The University HealthSystem Consortium (UHC) is an alliance of 117 AMCs and 310 affiliated hospitals, representing >90% of such institutions in the U.S.  We queried the UHC Clinical Data Base/Resource Manager™ to obtain hospital-level insurance and LOS and mortality data for inpatients discharged from a general medicine service between January 2012 and December 2014 using the 2014 risk-adjustment model.  We stratified hospitals according to state Medicaid-expansion status, defining Medicaid-expansion states as those that had expanded Medicaid by the end of the second quarter of 2014.  We then evaluated the proportion of discharges by payer, LOS index, and mortality index in Medicaid-expansion and non-expansion states pre- and post-ACA implementation (January 1, 2014).

Results:  We identified 4,173,605 discharges among general medicine patients from 204 hospitals in 37 states and the District of Columbia (DC).  Among the 21 Medicaid-expansion states and DC, the proportion of Medicaid discharges increased from 20.0% to 23.7% (P<0.001) after ACA implementation, while uninsured discharges decreased from 5.2% to 2.3% (P<0.001).  Among the 16 non-expansion states, the proportion of commercial discharges increased from 22.2% to 23.1% (P<0.001), while uninsured discharges decreased from 9.1% to 8.4% (P=0.001).  Among Medicaid-expansion states, the overall LOS index changed minimally pre- to post-ACA implementation (1.015 to 1.005, P=0.098) and actually improved for Medicaid patients (1.083 to 1.065, P=0.015).  Among non-expansion states, the overall LOS index improved pre- to post-ACA implementation (1.016 to 1.002, P=0.043).  The mortality index improved significantly pre- to post-ACA implementation for both Medicaid-expansion (1.016 to 0.889, P<0.001) and non-expansion states (1.006 to 0.856, P<0.001).  Despite these differences from pre- to post-ACA implementation, LOS index and mortality index did not differ significantly between Medicaid-expansion and non-expansion states either pre- or post-ACA implementation.

Conclusions:  LOS index and mortality index among general medicine patients at U.S. AMCs were not influenced by state Medicaid-expansion status.