Chronic obstructive pulmonary disease (COPD) has four stages, I to IV, with stage I being the mildest stage and stage IV the most advanced.
These stages reflect the fact that
COPD is a progressive disease that usually worsens over time.
The conventional way that doctors stage COPD is according to the results of the person's pulmonary function tests (also called lung function tests). These are special tests that provide measurements of how much air a person's lungs can hold (the "forced vital capacity," or FVC) and how quickly they can breathe out (the "forced expiratory volume in one second," or FEV1). Doctors compare a person's FVC and FEV1 to predicted numbers that reflect normal lung function in people of the same age, height, and gender. By seeing how much worse lung function is compared to the normal predicted numbers, one can determine the stage of COPD.
This is how COPD is usually staged:
Stage I: Mild COPD
FEV1 is at least 80 percent of normal. In this stage, people may or may not notice any symptoms.
Stage II: Moderate COPD
FEV1 is between 50 and 80 percent of normal. In this stage, people usually experience some shortness of breath with exertion; they may or may not have chronic cough.
Stage III: Severe COPD
FEV1 is between 30 and 50 percent of normal. In this stage, people usually are often tired and short of breath. They may have frequent exacerbation flares (or "flare-ups") requiring extra treatment or even hospitalization.
Stage IV: Very Severe COPD
FEV1 is less than 30 percent of normal; or FEV1 is less than 50 percent of normal and chronic respiratory failure is present (meaning the person needs chronic oxygen therapy). In this stage, people are often short of breath even at rest.