C3. Assessing the severity of COPD

Spirometry is the most reproducible, standardised and objective way of measuring airflow limitation, and FEV₁ is the variable most closely associated with prognosis (Peto 1983). The grades of severity according to FEV₁ and the likely symptoms and complications are shown in Box 4. However, it should be noted that some patients with an FEV₁ >80% pre­dicted, although within the normal range, may have airflow limitation (FEV₁/FVC ratio <70%).

A Spanish cohort study of 611 COPD patients found that the British Thoracic Society classification (which is very similar to Box 4) had the optimal sensitivity and specificity against the criterion of all cause and respiratory mortality over 5 years (Esteban 2009). There were also significant differences in health-related quality of life (HRQoL) between different stages of the disease [evidence level III-2].

Exacerbations are an important complication of COPD (see X: Manage eXacerbations). The future risk of exacerbations should be assessed in patients with COPD. Exacerbations are more frequent with increased severity of COPD. The most important risk factor for exacerbations is a history of past exacerbations; other factors include gastro-oesophageal reflux, poorer quality of life and elevated white cell count (Hurst 2010). A systematic literature review that included data from 76 studies confirmed that a past history of exacerbations is the most important predictor of future exacerbation risk (Hurst 2022) [evidence level I].