COPD Stages and How Smoking Drives Them

This page is general information from public health sources, not a diagnosis. Only a clinician can tell you what stage of COPD you have, and that takes a breathing test.

What are the stages of COPD?

Doctors grade COPD by how much airflow you have lost. A spirometry test measures how much air you can breathe out forcefully in one second, called FEV1, and compares it to the value predicted for your age, sex and height. British Columbia’s PharmaCare criteria for COPD inhalers are one of the few government pages that print the bands. As of 27 October 2026 they read:

Grade	FEV1 (percent of predicted)
Moderate	50% to under 80%
Severe	30% to under 50%
Very severe	Under 30%

The same criteria require a post-bronchodilator FEV1/FVC ratio below 0.70 before these grades apply. That ratio compares the air you blow out in one second with your total breath out, measured after you use an inhaler. The BC page does not define a mild category, so we do not either. Health Canada and the Public Health Agency of Canada also describe COPD without numbered stages, so if a clinician gives you a stage, ask what test result sits behind it.

How is COPD tested?

With spirometry. HealthLinkBC describes it as a painless test done in a doctor’s office or hospital: you breathe in as deeply as you can, then blow out as hard, fast and completely as possible into a mouthpiece. It shows how much air your lungs move and how quickly.

What are the symptoms as COPD progresses?

Health Canada says the main symptom is shortness of breath during everyday activities, often with frequent coughing and excess phlegm, and that symptoms develop over several years. The Public Health Agency of Canada adds that symptoms do not usually appear before age 55, although the lung changes begin many years earlier, and that COPD progresses slowly. Greater severity is linked to more frequent flare-ups and further loss of airflow.

A flare-up, which HealthLinkBC calls a COPD exacerbation, is a sudden worsening of symptoms. In an emergency, call 9-1-1 or your local emergency number.

How much does smoking have to do with it?

Most of it. The Public Health Agency of Canada says cigarette smoking accounts for 80% to 90% of COPD cases. Health Canada reports that about 80% of COPD deaths are due to smoking, and that people who smoke and have COPD are 22 to 26 times more likely to die from it than non-smokers. It also reports that more than 2 million Canadians aged 35 and older had diagnosed COPD in 2015-2016. Smoking was not the only cause listed by the Public Health Agency of Canada; workplace dust and fumes, outdoor air pollution, repeated childhood respiratory infections and a genetic deficiency of a protein called alpha-1-antitrypsin are others.

If you have smoked for decades and have a morning cough that never leaves, see the guide to smoker’s cough and when to see a doctor. The damage described in smoker’s lungs versus healthy lungs is what spirometry picks up later as lost airflow.

Does quitting help at every stage?

Yes. Health Canada says quitting smoking is the single most effective intervention to prevent further lung damage, that the risk of dying from COPD falls after quitting, and that quitting helps at any age, even after long-term heavy smoking. HealthLinkBC says COPD cannot be cured, but medicines and lifestyle changes may reduce symptoms, and the best way to slow it is to stop smoking. Health Canada lists treatment with drugs, oxygen therapy and surgery.

The quitting timeline shows what changes first. Long-term smokers worried about lung cancer rather than COPD can check the lung screening eligibility rules, and the pack-year calculator helps put a number on your history.