Black adults in the United States are more likely to have unrecognized emphysema than white adults in part because of this practice, says the presenting author, Gabrielle Liu, MD, a pulmonary and critical care fellow at Northwestern University Feinberg School of Medicine in Chicago. “Our study shows that many Black men with ‘normal’ lung function actually have evidence of abnormal lung health or emphysema,” she says.
Over 3 Million Americans Have Emphysema
More than three million people in the United States are living with diagnosed emphysema, according to the American Lung Association. The condition is a type of chronic obstructive pulmonary disease (COPD). In healthy people, the air sacs in the lungs are elastic and stretchy and can expand and deflate with each breath, but in people with emphysema, damage to the air sacs makes it harder for the lungs to move oxygen in and carbon dioxide out of the body. With emphysema, the body does not get the oxygen it needs to function properly, and a person will experience symptoms such as frequent coughing, wheezing, and shortness of breath, according to MedlinePlus. If emphysema is left untreated, the disease may progress more quickly and lead to heart problems and worsening respiratory infections.
The Use of Race-Specific Norms to Interpret Spirometry Results Dates Back to Slavery
Spirometry is a commonly used test of lung function. In the test, the patient blows into a tube connected to a spirometer, a machine that measures how much air a person is able to exhale and inhale. This is the standard respiratory function test used for the detection of COPD, including emphysema. It’s standard practice (promoted in the 2019 guidelines of the American Thoracic Society) to interpret results from spirometry using race-specific norms, which leads to a decrease in the predicted lower limit of “normal” for FEV1 and FVC for Black patients. FEV1 is the maximum amount of air a person can forcibly exhale in one second and FVC is the forced vital capacity — the maximum amount exhaled forcefully after a deep breath. That means that two men — one Black and one white — who have the same age and height could have the exact same lung function, but the lung function tests could be interpreted as “normal” for a Black man and “abnormal” for a white man, explains Dr. Liu. This practice of “race correction” for the interpretation of pulmonary function dates back to the era of U.S. slavery, when it was found that enslaved people had lower lung function relative to slaveholders, a difference that was mistakenly attributed to biology rather than social and environmental factors, experts say. The modern scientific basis of the race correction is theories about anthropometric differences, including the idea that white Americans of European descent have a larger trunk to leg ratio, and consequently higher lung volumes, than Black Americans.
More Black Men Are Likely to Go Undiagnosed for COPD Because of Race-Based Adjustments
Investigators evaluated the association between self-identified race and evidence of emphysema on CT scans in people with normal spirometry who were subjects in the multicenter Coronary Artery Risk Development in Young Adults (CARDIA) study, which followed Black and white participants starting in 1985. A total of 2,674 participants were included: 485 Black men, 762 Black women, 659 white men, and 768 white women. Each subject had a CT scan when they were an average age of 50, and spirometry results when they were an average age 55. Research divided the participants according to sex, and they adjusted their estimates to account for height, which has been associated with greater lung capacity. According to guidelines, an FEV1 of 80 to 120 percent of predicted FEV1 value is in the normal range.
In participants with an FEV1 between 80 percent and 99 percent of the predicted FEV1 value, Black men had a higher prevalence of emphysema than white men (15.5 percent versus 4 percent). Black women also had a higher prevalence of emphysema than white women (6.9 percent versus 3.2 percent).
In participants with an FEV1 between 100 percent and 120 percent of predicted FEV1 value, Black men also had a higher prevalence of emphysema than white men (14.6 percent versus 1.7 percent). Black women and white women had similar rates of emphysema in this grouping (3.8 percent versus 1.9 percent).
“We found that significant racial disparities in emphysema prevalence occur predominantly among those with FEV1 between 80 and 120 percent of that predicted,” says Liu. “This suggests that the greatest potential for misclassification using race-specific equations occurs among Black adults who are at risk of disease and who could potentially benefit from risk-factor modification.” Previously published studies have also shown that race-specific interpretations lead to underestimation of respiratory symptom severity and mortality in Black men, says Liu. A study presented at last year’s ATS conference concluded that when the race correction was removed, Black individuals had a significantly higher prevalence and severity of lung disease. “We believe our findings support reconsidering the use of race-specific interpretations of lung function in favor of race-neutral interpretations, as well as the incorporation of CT imaging into the evaluation of those with suspected impaired respiratory health and normal lung function,” says Liu.
