Stages of COPD

The basic "standard" for evaluating the severity of COPD has primarily been spirometry, also known as the Pulmonary Function Test (PFT).

However, functional dyspnea, body mass index (BMI), and FEV1 from Spirometry, when evaluated collectively, offer better insight into outcomes such as survival. Most times, the spirometry results are the only referenced statistics.

Spirometric Classification
The normal lung function, when measured with Spirometry, diminishes approximately 5% every 10 years after age 35 years old. Therefore, it is rare for a person over 35 to have a “100%” In addition, the normal values for the FVC and FEV (2 of the measurements in a pulmonary function test) vary depending on age, height, sex and race. The numbers are higher for:

35 years old vs 65 years old

Taller than shorter builds

Men than women

Caucasian than most other races.

The number used (FEV1) is a percent of the average expected of someone of your height, age, sex and race. It is expressed as a percent of predicted. Any number over 80% is considered normal

STAGE		Symptoms	Pulmonary Function Tests (PFT) with an FEV1 result of:
STAGE I	mild	Often minimal shortness of breath with or without cough and/or sputum. Usually goes unrecognized that lung function is abnormal	> 80% of predicted
STAGE II	moderate	Often moderate or severe shortness of breath on exertion, with or without cough, sputum or dyspnea. Often the first stage at which medical attention is sought due to chronic respiratory symptoms or an exacerbation	50-80% of predicted
STAGE III	severe	more severe shortness of breath, with or without cough, sputum or dyspnea - often with repeated exacerbations which usually impact quality of life, reduced exercise capacity, fatigue	30 – 50% of predicted
STAGE IV	very severe	appreciably impaired quality of life due to shortness of breath - possible exacerbations which may even be life threatening at times	Less than 30% of predicted - or less than 50% with chronic respiratory failure

The above chart is based in part on the Global Initiative for Chronic Obstructive Lung Disease.

Functional dyspnea
As assessed by the Medical Research Council dyspnea scale.

0: not troubled with breathlessness except with strenuous exercise.
1: troubled by shortness of breath when hurrying or walking up a slight hill.
2: walks slower than people of the same age due to breathlessness or has to stop for breath when walking at own pace on the level.
3: stops for breath after walking ~100 m or after a few minutes on the level.
4: too breathless to leave the house or breathless when dressing or undressing.

BMI is easily obtained by dividing the weight (in kg) over the height (in m²). Values less than 21 kg•m^-2 are associated with increased mortality.

Note: The words dyspnea and dyspnoea are often interchanged.