Washington (CNN) -- Nearly half of all Americans under the age of 65 have health conditions that could prevent them from getting insurance if the Republican effort to repeal health care reform is successful, U.S. Health and Human Services Secretary Kathleen Sebelius said Tuesday.
Sebelius said 129 million people -- nearly half of all Americans under the age of 65 -- have some form of pre-existing condition that could make them ineligible for coverage should they lose or change jobs, get divorced or face other changes that force them to seek new insurance.
That number includes 50 million people with more severe conditions that would almost certainly preclude or significantly increase the cost of individual coverage, Sebelius said.
House Republicans began debate Tuesday on repealing the measure, which requires insurers to cover children with pre-existing conditions and gives people with health conditions access to a temporary program providing insurance coverage.
Starting in 2014, it prohibits insurers from using health status in determining eligibility or calculating premiums, eliminates coverage limits and allows individuals and small businesses to shop for insurance plans through state-based exchanges.
Republicans say the law will harm the economy without containing health care costs.
The debate gives the administration the opportunity to "remind people of what's at stake, remind people of why we can't go back to where we were," Sebelius said on a conference call that included three people who said they have already seen positive changes in their lives as a result of health care reform.
One of them, Dawn Josephson of Jacksonville, Florida, said the legislation had made it possible for her family to afford comprehensive health coverage by prohibiting insurers from excluding her son's eye condition from coverage.
"It's a substantial financing savings and an emotional savings as well," she said. "If this got overturned, it would put our family right back where we were last summer."
The HHS analysis said as many as 82 million Americans with job-based coverage have a pre-existing condition that would complicate efforts to get coverage if they were to leave their jobs.
Between 9 million and 25 million uninsured people have a pre-existing condition, according to the HHS analysis
And the agency said between 4 million and 17 million children have a pre-existing condition, and that 2 million of those are uninsured.