COPD is confirmed by the use of spirometry - tests which estimate lung volume. FEV1(Forced Expiratory Volume) is the amount of air that can be forcefully expelled in one second and FVC (Forced Vital Capacity) is the amount of air expelled in one breath. Both values are dependent on age, height and sex but a low FEV1:FVC ratio indicates narrowing of the airways.

COPD can be classified according to FEV1 values:

• FEV1 at least 80% of predicted value = Mild COPD
• FEV1 between 50% and 79% of predicted value = Moderate COPD
• FEV1 between 30% and 49% of predicted value = Severe COPD
• FEV1 less than 30% of predicted value = Very severe COPD

FEV1 values are also used to determine the therapeutic approach following NICE guidelines (see below).