An estimated 27 percent of adults under the age of 65 have health conditions that would likely leave them uninsurable without the Affordable Care Act, according to a recent report by the Kaiser Family Foundation.
Roughly 52 million adults would left without coverage based on medical underwriting practices used in the vast majority of the state individual markets prior to the ACA, Kaiser said.
While the vast majority of the 52 million have coverage through an employer or public program such as Medicaid, the Kaiser report said the estimate showed how many people could be ineligible for individual market insurance should they lose coverage, as often happens because of career changes and moves.
Under Obamacare, people cannot be denied health insurance due to a pre-existing condition, which has been an expensive proposition for insurers.
Numerous payers such as UnitedHealth and Aetna have left the ACA market since it began in 2014, citing financial losses. Premiums on the exchanges have risen, in some cases to double-digits, for those getting Obamacare coverage in 2017.
President-elect Donald Trump has promised that Americans with pre-existing conditions will have access to health insurance, even after he dismantles Obamacare. However, Trump has also said he's against the individual and employer mandate, which the ACA put into place to get healthier and younger consumers into the market and make plans more affordable.
Prior to the ACA's coverage expansion, Kaiser estimated that 18 percent of individual and market applications were denied.
"To what extent people with pre-existing health conditions are protected is likely to be a central issue in the debate over repealing and replacing the ACA," the Kaiser report said.
The Trump administration's transition team has suggested bringing back state high risk pools for consumers with a pre-existing conditions who haven't maintained continuous coverage, according to CNN Money.
Prior to Obamacare, 35 states maintained high risk pools that often had waiting lists, charged premiums of up to 250 percent compared to plans for healthy individuals, had high deductibles and low benefit coverage, according to CNN Money, which sourced the Institute for Health and Disability Policy Studies at the University of Kansas.
However, risk pools often lost money, with about 50 percent of their operating costs subsidized by the state, the report said.
House Speaker Paul Ryan's "A Better Way" plan calls for providing at least $25 billion in federal funding for these programs, as well as placing caps on their premiums and banning wait lists.
A Kaiser Family Foundation poll found the 53 percent of people reported that they or someone in their household has a pre-existing condition.
The rates of declinable pre-existing conditions vary from state to state. On the low end, in Colorado and Minnesota, at least 22 percent of non-elderly adults have conditions that would likely be declinable if they were to seek coverage in the individual market under pre-ACA underwriting practices.
Rates vary from around 22 to 23 percent in the northern and western states to 33 percent in some southern states.