(CNN) Obamacare eliminated the costs and out-of-pocket expenses for Americans wanting preventive health care services -- including mammography and colonoscopy, both tests able to detect cancer.

Among older Americans, use of mammography increased under Obamacare, according to a study published Monday in the journal Cancer. But another preventive screen test, colonoscopy, didn't see a similar increase.

Offered a free mammogram, more women of all income and education levels accessed the test, according to Dr. Gregory Cooper, lead author of the study and program director of gastroenterology at University Hospitals Cleveland Medical Center and the Case Comprehensive Cancer Center.

"We wanted to see, as a natural experiment, what happens when you change the financial burden on preventive services," Cooper said.

President-elect Donald Trump and the Republican Party have said they will " repeal and replace " the health care program, which was signed into law in 2010, with most parts of the plan phased in by 2014. It remains unclear which parts will remain and which will be replaced.

"We don't know what the future of Obamacare is," Cooper said, though he's heard that some pieces of the Affordable Care Act may be rescued, such as coverage of dependents up to age 26 and those with pre-existing conditions.

"I haven't heard anything about preventive services, but I would argue that, even if the program itself is dismantled, that would be a worthy benefit to keep," Cooper said.

Mining the data

To tally how many people used mammography and colonoscopy preventive services before and after Obamacare, Cooper and his colleagues examined Medicare claims data for beneficiaries 70 or older.

They chose this group because they had access to data and were interested in longitudinal effects of Obamacare. "We were actually able to look at the same folks before and after," Cooper said. "So that was one advantage."

They identified women who had not had a mammogram in the previous two years and both men and women who had not undergone a colonoscopy in the past five years. Then, using claims data, Cooper and his colleagues compared the women and men who got tested in the periods before and after the Affordable Care Act: 2009 to 2010 versus 2011 to 2012.

Medicare uses a guideline of mammography testing every one to two years for women age 40 years and older, according to the 2002 standard set forth by the US Preventive Services Task Force , an independent, volunteer panel of national experts in prevention and evidence-based medicine. (The task force has proposed a more recent guideline , which has not yet been adopted by Medicare.) When it comes to colonoscopy, the task force recommendation is to get tested starting at age 50 and continuing until 75.

"We know that more affluent people are more likely to get screened," Cooper said. "If you take away some of the financial barriers, would the gap between the poorest and wealthiest begin to narrow?"

Narrowing the gap

After out-of-pocket expenses were eliminated under Obamacare, the rates of women getting mammograms increased. Though women with lower incomes and education levels were tested less, the cancer screening gap narrowed between the more- and less-affluent groups.

For colonoscopy, there were no real changes in testing numbers after Obamacare. In both periods, to some extent, higher socioeconomic status predicted testing.

"At least for mammography, (the study results) are largely consistent with what we know from prior research," said David H. Howard, associate professor in health policy and management at Emory University's Rollins School of Public Health, who was not involved in the research. He believes the low uptake of colonoscopy is due to non-financial barriers, including the invasiveness of the procedure.

"In terms of bang for the buck, it's one of the more valuable cancer screening services," Howard said, adding that reduced cost-sharing does not have much of an effect. "Generally, a lot of people don't get colonoscopy, even though it's recommended."

According to both Howard and Lauren Hersch Nicholas, an assistant professor of health economics at Johns Hopkins School of Public Health, the study results are similar to previous studies that looked at health care utilization: Generally, it is known that when people have to pay more for medical care, they get less of it.

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However, said Nicholas, who was also not involved in the study, the "study does not provide enough information to know whether the observed trends over time are due to the ACA changes or any number of other changes," such as differences in the health of patients or their awareness of screening.

Howard agreed. "Always with this type of study, it's hard to tie the changes we see directly to the change in policy."

Still, the study detected a positive trend in mammography testing overall.

"The gap narrowed," said Cooper. "Maybe in the pre-Affordable Care Act-era, that was a barrier: the out of pocket expense."