Study objective: To assess the relevance of sputum production to pulmonary function, in particular, persistent obstruction in patients with a primary clinical diagnosis of asthma.
Design: Cross-sectional study of all patients currently followed up in secondary care in a defined locality.
Setting: National Health Service and private clinics in north-east England.
Patients: All attenders, aged 18 years or older, with asthma, confirmed by reversibility of peak expiratory flow (PEF) by ≥15% and to ≥200 L/min.
Interventions: Pro forma history. Pulmonary function at attendance. Assessment of best function according to protocol. Measurement of actual FEV1 FVC, and PEF at attendance.
Measurements and results: We studied 772 subjects; 387 (50%) were male; mean age was 55 years; atopic, 51%; current smokers, 11.5%; ex-smokers, 36%; and never smokers, 52.5%. Best pulmonary function was lower in chronic sputum producers (PEF, 83.2 vs 95.8; FVC, 67.9 vs 81.7% predicted). Chronic sputum production and its negative relationship with best function was strongly associated with smoking. There was little relationship between chronic sputum and persistent obstruction in nonsmokers. There were no univariate associations between sputum during attacks, or its color, and pulmonary function, but after allowing for demographic factors, including smoking, green sputum was associated with persistent obstruction. There was little relationship between sputum and actual/best function at attendance.
Conclusions: Chronic sputum production is associated with persistent obstruction principally in those who have smoked, suggesting that the association reflects smoking rather than asthma. There is no interaction with atopy. After allowance for cigarette smoking, there is an association between green sputum production during exacerbations and persistent obstruction. Green sputum during relapse in asthma may indicate inflammation that is relevant to prognosis.