"In the second quarter alone, Tenet saw a $78 million reduction in unpaid care," the report said.
The difference in the experience of health systems in expansion and nonexpansion states was underscored by HCA Holdings. In expansion states, HCA saw a 48 percent plunge in uninsured admissions, and a 32 percent rise in Medicaid admissions.
In nonexpansion states, HCA saw just a 2 percent drop in its uninsured admission rate.
The positive effect of its business in expansion states was reflected over the summer, when HCA revised its earnings outlook to reflect what it said would be a bigger-than-expected windfall from Medicaid expansion and private insurance plans sold through the health-care exchange.
PwC's report found Medicaid expansion has "had a similar effect on doctors," with primary care physicians and others seeing a higher percentage of Medicaid patients in the first quarter of this year than their counterparts in nonexpansion states.
The report comes amid continued debate over Medicaid expansion and as 7.2 million people have signed up for Medicaid since last fall. Not all of those newly enrolled were newly eligible, but the expansion of Medicaid and the rollout of the Affordable Care Act have been credited with a big boost in the enrollment rate in expansion states.
The ACA originally mandated that every state and the District of Columbia expand their Medicaid programs to cover nearly all adults who earn up to 138 percent of the federal poverty level, or about $16,105 for an individual and $32,913 for a family of four. Traditional Medicaid programs, which are jointly run by state and federal governments, often do not cover adults without children, or cap eligibility for benefits at very low incomes for adults with dependent children.
The expansion of Medicaid was supposed to work in concert with another aspect of Obamacare, which makes subsidies available to people who earn between 100 to 400 percent of the federal poverty level, and who buy private insurance plans through state health-care exchanges as well as
But the 2012 Supreme Court decision that upheld the ACA requirement that nearly all Americans obtain health coverage this year or pay a penalty also found that Medicaid expansion would be decided on a state-by-state basis.
So far, Medicaid expansion has been adopted by 26 states and the District of Columbia.
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Pennsylvania's version of expansion was approved last week, and will begin Jan. 1 Governors of five other states are making moves to expand or are seriously discussing that prospect.
Unlike traditional Medicaid, where state and federal governments split the costs, the federal government is footing 100 percent of the costs of covering the newly eligible under Medicaid expansion through 2016. After that, the federal government's share of the costs will decrease gradually, but are set to level out at 90 percent—much higher than its share under traditional Medicaid in any state.
Aaron Albright, a spokesman for the Centers of Medicare and Medicaid Services, said, "Medicaid expansion is helping millions of Americans access health coverage, many for the very first time. Increased coverage reduces hospitals' uncompensated care and lowers cost shifting to businesses and everyday Americans that see higher health insurance premiums when those costs are passed on to them."
—By CNBC's Dan Mangan