Cough and phlegm are common in COPD. Previous studies have shown conflicting evidence regarding their association with mortality and lung function. We sought to better understand how cough and phlegm impact mortality and lung function in COPD. We analyzed data from the Lung Health Study, consisting of 5,887 smokers with mild to moderate airflow obstruction followed longitudinally. We assessed the association between baseline symptoms of cough alone, phlegm alone, and cough and phlegm with 12.5-year mortality and annual lung function decline. Average age at entry was 48.5 years (± 6.8) with 63% males and 4% African Americans. Cough alone was present in 17%, phlegm alone in 12%, while 31% had both. Neither symptom alone was associated with death, but the combination was associated with increased risk of death after adjustment for age, gender, race, smoking status at year 5, pack-years smoked, randomization group, baseline FEV1 percent predicted (HR 1.27, 95% CI 1.02-1.59). Individuals with cough and phlegm together more commonly died of respiratory causes than those without. Cough with phlegm was associated with 48 mL lower baseline FEV1 (95% CI -90, -6), while neither symptom alone was associated with baseline FEV1. No symptom was associated with FEV1 longitudinally. Cough and phlegm together are associated with mortality and lung function decrement in mild-to-moderate COPD, independent of lung function and smoking status. Respiratory causes of death are common among those with cough and phlegm. Such information can help to identify subsets of individuals with COPD having higher risk for adverse outcomes.
Keywords: Symptoms; lung function.; subtypes; survival.