Up to 6.3 million people could end up paying substantially higher premiums if a bill similar to the House's Obamacare replacement becomes law, according to the Kaiser Family Foundation.
The American Health Care Act would allow states to authorize insurers to charge customers based on their medical status if they went without insurance for at least 63 days. Under the Affordable Care Act, insurers can only charge smokers and customers in limited age-rating bands different premium prices.
That policy change could impact up to 6.3 million Americans, according to KFF's study released Wednesday. However, the estimate is uncertain for a lot of reasons.
The estimate assumes all states will return to medical underwriting. Some may do so, in the hopes that it could lower premiums for the majority of buyers in the exchanges. But ending protections for pre-existing conditions is politically unpopular, and some members of Congress said they believed few states would change the rules in this way.
"What states decide to do may ultimately have the greatest effect on how many people with pre-existing conditions face potentially unaffordable insurance premiums," the study said.
The House bill does provide support to customers who end up getting punished for being uninsured, either through reinsurance, which they call "invisible high risk pools," or through high risk pools.
The Kaiser Family Foundation's study bases its estimate on data for how many adults not covered by Medicare had a gap in coverage of three months or more in 2015. It then takes 23% of that population, which is what proportion of adults have conditions that insurers used to reject as too costly before the protections of the Affordable Care Act.
The study's estimate also assumed that all people who leave health insurance for months at a time would need to get into the individual market eventually. But some of those people might get a job that offers health insurance, or marry someone with a job that offers health insurance. Since 49% of those with coverage gaps are at or below the income levels that are covered under the Medicaid expansion, many of those with gaps may return to Medicaid.
However, the AHCA would make Medicaid more difficult to access for able-bodied adults with no minor children, because states would have to pay their full match to cover them when they re-enter the program; 19 states never offered Medicaid to this population.
"People with health conditions would have a strong incentive under an AHCA waiver to maintain continuous coverage in order to avoid being charged premiums that could potentially price them out of the insurance market altogether," the study said.
However, since the AHCA premium tax credits are generally less generous than ACA subsidies, it's an open question of how many would be able to keep up with premiums to stay covered, the study said.