A new study finds that 52 million non-elderly Americans have the sort of pre-existing conditions insurers cited to deny them health insurance coverage in the pre-Affordable Care Act world. The study, released Monday by the Kaiser Family Foundation, notes that a majority of those Americans are covered by group health plans where they would not face such medical underwriting. But it adds that, due to market churn, many more than just the 8 percent or so of consumers who currently receive coverage through the individual marketplace stand to be affected if the pre-existing conditions provision of Obamacare is dismantled.

“For many people, the need for individual market coverage is intermittent, for example, following a 26th birthday, job loss, or divorce that ends eligibility for group plan coverage, until they again become eligible for group or public coverage,” the study said.

Exactly what conditions insurers could cite to deny Americans coverage varied state-by-state before the the ACA’s pre-existing conditions provisions was fully implemented in 2014. In some states, like Minnesota, an estimated 22 percent of the population had conditions that insurers could use to deny them coverage. In others, like West Virginia, the potentially uninsurable made up 36 percent of the non-elderly population. Overall, about 27 percent of Americans have the pre-existing conditions insurers could use to deny them coverage.

A vast majority of states had lists, pre-ACA, of deniable conditions, which commonly included maladies ranging from cancer and kidney disease to mental disorders and sleep apnea.

Additionally, some insurers could deny coverage on the basis of consumers’ occupation, including coal miners, meat processor, firefighters, security guards, pilots and taxi cab drivers.

The study notes that, in addition to denying people coverage entirely on the basis of pre-existing conditions, insurers before Obamacare could use other tactics to discriminate against those consumers. For instance, some consumers faced exclusion riders, which would exempt treatment for specific conditions or for particular body parts from their coverage. Others were only covered with a surcharge on premiums, or faced higher deductibles.

Pre-existing conditions coverage is a provision of Obamacare that some Republicans, including President-elect Donald Trump, have said they would like to preserve in an eventual GOP replacement for Obamacare. Other Republicans have proposed using a continuous coverage standard instead, which would prohibit insurers from discriminating on the basis of pre-existing conditions only if the consumer maintains continuous coverage.

If Republicans move forward with repealing Obamacare via the legislative maneuver known as reconciliation — akin to the repeal bill lawmakers passed but President Obama vetoed in January — then Obamacare’s pre-existing conditions would remain in effect, at least during the transition phase into a to-be-determined ACA alternative. Health policy experts have warned, however, that keeping the pre-existing conditions provision on the books without the ACA’s individual mandate, which could be repealed right away, risks major chaos in the individual markets.