More people may die from undiagnosed lung cancer because they don’t qualify for low-dose CT scans, according to a study by Mayo Clinic researchers. The researchers blame current screening guidelines that have remained the same despite the decline in smoking rates in the U.S.

“Our data raise questions about the current recommendations,” said Mayo pulmonologist, Dr. David E. Midthun, one of the study authors. “We do not have the best tool to identify who is at risk for lung cancer.”

Over the study period the percentage of lung cancer patients who would have been eligible for CT screening under current guidelines fell dramatically: from 56.8% in 1984-1990 to 43.3% in 2005-2011. The proportion of men who would have been eligible decreased from 60% to 49.7%, while the percentage of women dropped from 52.3% to 36.6%.

Researchers worry about the trend. “We don’t want to disincentive patients to stop smoking,” Midthun told CNN in a phone interview. “When I told one of my patients about the study, his first question was, ‘If I stop smoking will I have to stop screening?’”

“We want people to stop smoking, and we don’t want them to lie or continue smoking just so they can be screened,” added Midthun. “We need better tools to make risk calculations for those who should be screened.” “There’s nothing magical in 30-year pack history,” added Midthun. He told CNN that age is an equally important factor. “For example, if a person stops smoking at age 55, his risk of lung cancer at age 70 is higher than it was at age 55 when he quit.”

The study was published in the February 24, 2015 issue of JAMA, the journal of the American Medical Association. It was funded by the Mayo Clinic and grants from the National Institutes of Health and the National Institute on Aging.