Chronic obstructive pulmonary disease (COPD) is classified into four stages. The stage a person is at is determined by how well they perform on a spirometry test. A spirometry test is a simple test that shows the amount of air a person can exhale and how long it takes him to do so. The first stage is mild COPD, where there may be minimal shortness of breath and symptoms often go unnoticed. In the second stage, known as moderate COPD, you may experience shortness of breath, especially if you exert yourself. It is usually during the moderate stage that people first seek medical advice. The third stage is severe COPD, where you will find yourself feeling short of breath more often and may experience frequent exacerbations of the disease. During the fourth stage, known as very severe, you will constantly be feeling short of breath and your inability to breathe properly may be life threatening at times.
At one point, COPD was classified into five stages, with the additional stage being stage zero: "At risk." This stage was classified as someone who has a chronic cough and produces a lot of mucus, but their spirometry test appears normal. This stage was removed from formal classifications due to a lack of evidence linking the symptoms of a chronic cough and mucus production to the development of COPD. In other words, while most people who develop COPD will start with symptoms of a chronic cough and increased mucus production, not all people who have these symptoms will go on to develop COPD. Although these symptoms are no longer a formal stage of COPD, if you have a chronic cough and are producing a lot of mucus, you should get it checked out by a doctor, as it may be early signs of COPD.