The researchers started with the Colorado All Payer Claims Database because the database collects claim records for all patients in the state with coverage through Medicare, Medicaid and private individual, family and group insurance plans.

The database also includes records for about half of the people in the state's self-funded employer health plans, and it links patient records to the U.S. Renal Data System, a national registry for patients with end-stage renal disease.

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The study period covered patients who began receiving dialysis in 2012 and 2013, or two years before the Affordable Care Act prohibited major medical insurers from considering patients' health status when selling or pricing coverage, and patients who began receiving dialysis in the two years after the ACA rules took effect.

Medicare, a federal health insurance program best known for providing coverage for people ages 65 and older, began providing coverage for people with end-stage renal disease, or severe kidney disease, in 1972.

The percentage of patients studied with known sources of coverage who managed to keep private coverage in place for a full year after starting dialysis increased to 5.8% in the two years after the new ACA rules kicked in, from 3.5% during the two years before the new ACA rules kicked in.

The researchers did not say how many of the privately insured individuals included in the analysis had employer-sponsored health coverage.

The percentage of patients with known sources of coverage who were enrolled in Medicare after a year of dialysis fell to 79%, from 88%.

The Medicare program itself provides some protection for employers who end up covering people who use kidney dialysis services for an extended period.

"Medicare is the secondary payer to group health plans for individuals entitled to Medicare based on ESRD for a coordination period of 30 months regardless of the number of employees and whether the coverage is based on current employment status," according to the Centers for Medicare and Medicaid Services, the agency that runs Medicare.

But the Wang study shows that an employer could spend more than $250,000 for a plan participant getting kidney dialysis throughout the 30-month coordination period.

The researchers suggest that the apparent shift away from universal Medicare enrollment for people getting dialysis could hurt Medicare's ability to encourage improvements in kidney care for all patients.

"The observed decline in Medicare enrollment signals fragmentation in payers for dialysis that may undermine Medicare's dominant position as the primary payer for dialysis and its influence to nudge improvements in access, cost, and quality via policy changes," the researchers said.