More than half of smokers with normal spirometry had some form of respiratory-related impairment associated with COPD, Dr. Elizabeth A. Regan and the Genetic Epidemiology of COPD (COPDGene) investigators reported in JAMA Internal Medicine.
The findings imply that up to 35 million current and former smokers older than age 55 years in the United States may have some form of respiratory-related impairment associated with COPD that has gone undiagnosed with standard spirometry, the researchers wrote (JAMA Internal Med. 2015 June 22 (doi:10.1001/jamainternmed.2015.2735).
They found that 55% of current and former smokers older than age 55 years in the study who did not meet the spirometric criteria for COPD (GOLD [Global Initiative for Chronic Obstructive Lung Disease] 0 score) had significant respiratory disease. Their conclusion was based on seven metrics: chronic bronchitis (seen in 12.6% of the GOLD 0 participants), history of severe respiratory exacerbations (seen in 4.3%), dyspnea score of at least 2 (seen in 23.5%), quantitative emphysema exceeding 5% (seen in 9.8%), quantitative gas trapping exceeding 20%, (seen in 12.2%), St. George’s Respiratory Questionnaire (SGRQ) total score exceeding 25 (seen in 26%), and a 6-minute walk distance of less than 350 m (seen in 15.4%).
In 108 never smokers, none had chronic bronchitis or respiratory exacerbations, 3.7% had dyspnea, 8.3% had quantitative emphysema exceeding 5%, 10.2% had quantitative gas trapping exceeding 20%, 3.7% had SGRQ scores above 25, and 3.7% had a 6-minute walk distance of less than 350 m.
Dr. Regan of National Jewish Health and the University of Colorado, Denver, and her associates gathered data from 21 sites across the United States regarding 8,872 current or former smokers who were between the ages of 45 and 80 years and were classified using GOLD spirometric criteria based on postbronchodilator spirometry: 4,388 had a GOLD 0 score, defined as a normal postbronchodilator ratio of FEV1 to forced vital capacity exceeding 0.7 and an FEV1 percentage of at least 80% predicted; 794 patients had a GOLD 1 score, defined as mild COPD; and 3,690 had a GOLD 2-4 score, defined as moderate to severe COPD.
Compared with 108 never smokers, the GOLD 0 group had a worse quality of life score (mean SGRQ total score 17.6 for GOLD 0 and 7 for never smokers) and a lower 6-minute walk distance (447 m vs. 493 m). In a subset of 300 patients in the GOLD 0 group whose CT scans were visually scored, 42% (127) had evidence of emphysema or airway thickening. In a subset of 100 never smokers, 10% had evidence of emphysema or airway thickening.
Current guidelines do not include treating smokers with normal spirometry, but physicians recognize the role of medication in treating symptoms and effective treatments need to be determined for GOLD 0 patients, the researchers said. Respiratory medications were being prescribed to 20% of the GOLD 0 participants in COPDGene who had at least one impairment, yet these patients reported more symptoms.