Expansion of Medicaid and newly created insurance exchanges would do more than high-risk pools to offer adults with pre-existing conditions access to affordable health benefits, the Commonwealth Fund said in a new report.

Risk pools to cover uninsured individuals who have pre-existing conditions would be "extremely expensive and likely unsustainable," the Commonwealth Fund said.

Under the Affordable Care Act, high-cost patients who have pre-existing conditions could be pooled with a larger population under Medicaid expansion and plans that are sold within newly created insurance exchanges, where subsidies for low- to mid-income households would make plans more affordable, the report said.

The Patient Protection and Affordable Care Act created a high-risk pool, the Pre-Existing Condition Insurance Plan, which launched in states between July and October 2010. Thirty-five states also operate alternative high-risk pools that cover a total of 226,000, according to the report.

The risk pools operate at a loss, the report said, and the Pre-Existing Condition Insurance Plan, which covers 78,000 and is financed through at one-time $5 billion allocation, has seen costs exceed projections.

The Pre-Existing Condition Insurance Plan does not subsidize household premiums, which by law are set at the rate paid by a healthy individual of the same age in the individual market. Some states do subsidize state risk pools, where premiums may be up to double the market rate, the report said.

"Given the general lack of affordability of high-risk pool coverage at the individual level and the high costs of plan operation, the potential of high-risk pools as a vehicle for coverage expansion remains quite limited," the report said.