Each stage of COPD is based on symptoms and measured loss of pulmonary function, especially the forced expiratory volume in the first second (FEV1). The FEV1 is the amount of air that can be forcefully expelled in the first second of exhalation. It is an indicator of airway obstruction and how far the disease has progressed. Normal is 80% or greater of the predicted value. The predicted value for a given individual is based on age, gender, height, and race or ethnicity.
There are 4 stages of COPD:
At risk Stage 0 Normal pulmonary function
Mild Stage I Mild reduction in air flow
Moderate Stage II FEV1 50 to 80% of predicted
Severe Stage III FEV1 30 to 50% of predicted
Very Severe Stage IV FEV1 less than 30% of predicted