Spanish researchers found nearly half of COPD patients in the study had potentially pathogenic bacteria in their airways. These can cause inflammation and worsen symptoms.
The presence of these bacteria was linked to darker sputum samples, suggesting sampling sputum could be a simple way of tracking COPD severity.
In the study, researchers studied 119 patients with COPD and assessed sputum samples provided over one year.
They found bacterial colonisation in 49 per cent of cases. More than 80 per cent of darker samples yielded potentially pathogenic bacteria when cultured, compared with just 44.7 per cent of lighter samples.
The presence of potentially pathogenic bacteria was also linked to increased dyspnoea.
The authors said: 'The identification of patients colonised by potentially pathogenic bacteria using a non-invasive and relatively inexpensive technique such as the analysis of sputum may play an important role in the management of severe COPD.'