The Global Initiative for Chronic Obstructive Lung Disease (GOLD) released a four-stage classification of chronic obstructive pulmonary disease (COPD) severity to guide the therapeutic approach

Stage 0 defines the condition characterised by classic clinical symptoms but normal spirometry.

Treatment:: Avoidance of risk factor(s); influenza vaccination

Stage I defines patients with a forced expiratory volume in one second (FEV₁)/forced vital capacity (FVC) of <70%, and an FEV₁ of >80% predicted, with or without chronic symptoms that may or may not be aware of disease status.

Treatment:: Add short-acting bronchodilator when needed

Stage II (FEV₁/FVC <70%, FEV₁ 30–79%) is split into

substages IIa (FEV₁ 50–79%)

Treatment::

Add regular treatment with one or more long-acting bronchodilators

Add rehabilitation

substages IIb (FEV₁ 30–49%) according to the greater rate of exacerbation experienced by patients in substage IIb, which in turn is inversely related to health status .

Treatment::

Add inhaled glucocorticosteroids if repeated exacerbations

Stage III (FEV₁/FVC <70% and either FEV₁ <30% pred, hypoxaemia, or clinical signs of right heart failure) is expected to be associated with the worst health status.

Treatment::

Add long term oxygen if chronic respiratory failure

Consider surgical treatments

Here is in table