The most common test of lung function, spirometry, probably is not detecting signs of emphysema in some people with the lung ailment, a new study says.
In particular, Black men are at greater risk of suffering from undiagnosed emphysema, since the way spirometry results are interpreted appears to “normalize” their bad lung function, said lead researcher Dr. Gabrielle Liu, an instructor of pulmonary and critical care medicine at Northwestern University Feinberg School of Medicine in Chicago.
The equations used to analyze spirometry results “incorporate race, and they basically normalize having a lower lung function if you’re a Black adult compared to a white adult,” Liu said.
A spirometry test measures how much air you can breathe in and out of your lungs, as well as how easily and fast you can blow air out.
Liu and her colleagues set out to see how well spirometry detects emphysema, a condition in which the air sacs of the lungs become damaged and enlarged. It is one of the conditions that comprise COPD (chronic obstructive pulmonary disease). More than 3 million Americans have emphysema, researchers said in background notes.
The researchers drew data from a heart and lung disease study that’s been ongoing since 1985. They looked at nearly 2,700 participants who’d had both a spirometry test and a CT scan as part of the study.
The investigators found that nearly 5% of people with normal spirometry results actually had signs of emphysema on their CT images.
In other words, based solely on spirometry, these patients would go undiagnosed.
That’s not completely surprising given what we’ve learned in recent years about spirometry, said Sanja Stanojevic, vice chair of the American Thoracic Society’s pulmonary function testing proficiency committee.
“We are learning as new research emerges that it’s a very blunt tool to identify lung disease,” she said.
“Our lungs are a really complex network of large airways, and they branch out into smaller and smaller airways,” Stanojevic continued. “We know that a lot of lung disease actually begins in the smaller airways. Spirometry is really good at telling us if there’s disease or impairment in the bigger airways.
“So by the time we can catch lung disease using spirometry, the diseases are well established because they originated from the smaller airways and we don’t have a lot of tools to identify disease in the small airways,” Stanojevic concluded.
An already flawed test is even less effective for Black patients because the equations used to interpret spirometry results assume that as a group their lungs function less effectively than those of whites, Liu added. This adds to racial disparities, the researchers said, although Black people still had higher rates of emphysema than white people when new equations were used that didn’t factor in race.
Using CT scans rather than spirometry to detect lung problems would be more accurate, but also would be too expensive, Stanojevic said. Such a move would probably exacerbate the racial disparities found in this study.
Instead, respiratory specialists probably could do a better job if they combined spirometry tests with other lung function tests and a complete health history for each patient, Stanojevic said.
“I certainly think that we can come up with tools that complement spirometry,” Stanojevic said. “Maybe that’s looking at people’s symptoms and people’s risk factors for a particular lung disease. Using that information together with spirometry might provide us the same information as if we were to put everybody in a CT scanner.”
In fact, Liu’s study found that cough-related symptoms were significantly higher among participants with CT-detected emphysema, about 55% compared with 39% for those without emphysema.
“Physicians now could consider ordering CT scans on patients who have normal spirometry, who also have respiratory symptoms to see if there’s any evidence of emphysema. And if they do find emphysema, the physician should really be discussing mitigating any potential risk factors that a patient could have,” Liu said.
“Are they smoking? Are they exposed to a lot of secondhand smoke? Are they using protective equipment at a job where they might be exposed to dust and fumes?” she said.
The new study appears in the July 19 Annals of Internal Medicine.
The American Lung Association has more about spirometry.
SOURCES: Gabrielle Liu, MD, instructor, pulmonary and critical care medicine, Northwestern University Feinberg School of Medicine; Sanja Stanojevic, PhD, vice chair, American Thoracic Society’s pulmonary function testing proficiency committee; Annals of Internal Medicine, July 19, 2022
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