The majority of long-term smokers and former smokers may be considered healthy after passing a lung-function test but still suffer respiratory-related impairments, according to a new study that evaluated patients closely with lung imaging, walking and quality-of-life tests. The research revealed that in some of the patients, the impairments are associated with early stages of chronic obstructive pulmonary disease (COPD).

The study, which is titled “Clinical and Radiologic Disease in Smokers With Normal Spirometry” and was recently published in JAMA Internal Medicine, focused on the diagnosis of the chronic progressive disease during the earliest phases. COPD is currently incurable and the third leading cause of death in the country, and the diagnosis is made by blowing into a spirometer that measures the amount of air.

“The impact of chronic smoking on the lungs and the individual is substantially underestimated when using lung-function tests alone,” explained in a press release the senior author of the study James D. Crapo, who is a professor of medicine at National Jewish Health. “Lung disease is common in smokers whose lung-function tests fall within population norms.”

The research team examined data from 8,872 patients between the ages of 45 and 80 and who smoked at least a pack of cigarettes a day for 10 years. Approximately half of the patients were rated disease-free, according to lung-function tests. However, other criteria, such as impairments in physical function, respiratory symptoms, CT scans, use of respiratory medications, and respiratory-specific quality of life revealed that 55% of the participants considered disease-free had some kind of respiratory related impairment.

Examining CT scans of patients initially classified as disease-free, the investigators discovered that 42% of them had emphysema or airway thickening, 23% significant shortness of breath, 15% walked less than 350 meters in six minutes. In addition, this group reported worse quality of life than patients who had never smoked, with 25% of the smokers having scores that exceeded a threshold considered clinically significant.

“Smokers who have ‘normal’ lung-function tests often have significant respiratory disease. Many of those smokers likely have the early stages of chronic obstructive pulmonary disease,” added the lead author of the study Elizabeth Regan, MD, PhD, who is an assistant professor of medicine at National Jewish Health. “We hope these findings will help debunk the myth of the healthy smoker and highlight the importance of smoking prevention and cessation to prevent lung disease and other long-term effects of smoking.”

The study authors also emphasized the importance of early detection of lung diseases such as COPD in order to enable early treatment, as well as symptom, function and quality of life improvements. Therefore, Crapo and Regan recommended long-term smokers and former smokers to discuss with their physicians getting lung CT screenings to detect early stages of lung cancer and COPD.