Chronic Obstructive Pulmonary Disease (COPD) is a progressive lung condition characterized by obstructed airflow that makes breathing difficult. It involves chronic bronchitis (inflammation and mucus production) and emphysema (destruction of air sacs). Classifying COPD severity uses a comprehensive assessment guided by the Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines. This system incorporates lung function, symptom burden, and the risk of acute flare-ups.
Defining Severity Through Lung Function
The initial assessment of COPD severity relies on spirometry, which measures how much air a person can breathe out and how quickly. The key metric is the Forced Expiratory Volume in 1 second (FEV1), the volume of air exhaled during the first second of a forced breath. COPD is diagnosed if the post-bronchodilator FEV1 divided by the Forced Vital Capacity (FVC) ratio is less than 0.70.
Once the diagnosis is confirmed, the FEV1 percentage of the predicted normal value is used to grade the severity of the airflow limitation into four physiological stages, known as GOLD Grades 1 through 4. This physiological grading system provides an objective measure of mechanical damage but does not fully capture the patient’s daily experience or future risk.
GOLD 1 (Mild obstruction) is defined by an FEV1 that is 80% or greater of the predicted value. GOLD 2 (Moderate obstruction) occurs when the FEV1 is between 50% and 79%. GOLD 3 (Severe obstruction) is present when the FEV1 falls between 30% and 49%. GOLD 4 (Very severe obstruction) is characterized by an FEV1 that is less than 30%.
Integrating Symptom Load and Exacerbation Risk
Modern classification refines the physiological stages by adding a matrix approach that incorporates the patient’s level of symptoms and their history of acute exacerbations. Symptom burden is measured using validated tools like the modified Medical Research Council (mMRC) dyspnea scale or the COPD Assessment Test (CAT). The mMRC scale measures breathlessness, while the CAT is a comprehensive questionnaire assessing cough, mucus, chest tightness, and activity limitation.
Symptom burden is categorized as low (mMRC score 0–1 or CAT score less than 10) or high (mMRC score 2 or greater or CAT score 10 or greater). Exacerbation history determines the patient’s risk of future deterioration. Low risk means zero or one moderate exacerbation not requiring hospitalization in the past year.
High risk is defined by having two or more moderate exacerbations or at least one exacerbation leading to hospital admission within the last year. Combining these criteria leads to a risk stratification system, revised in the 2023 GOLD guidelines to three groups (A, B, E). Group A represents low symptoms and low risk, Group B represents high symptoms and low risk, and Group E includes all patients with a history of high exacerbation risk, regardless of their daily symptom load.
Tailored Management Strategies for Each Group
The primary purpose of combining physiological severity with symptom and risk assessment is to guide specific treatment choices. Group A patients (mild symptoms, low risk) often start with a short-acting bronchodilator (SABA) used on an as-needed basis.
Group B individuals (high symptom burden, low risk) typically receive initial treatment involving a long-acting bronchodilator, such as a long-acting beta-agonist (LABA) or a long-acting muscarinic antagonist (LAMA). The 2023 guidelines often recommend starting with dual bronchodilation (LABA and LAMA combination) because this approach is more effective at controlling persistent symptoms.
Group E patients, defined by high risk of future exacerbations, are also typically started on a combination of a LABA and a LAMA for initial therapy. For those in Group E who also have elevated blood eosinophil counts, which are markers of a certain type of airway inflammation, an inhaled corticosteroid (ICS) may be added to the LABA/LAMA combination, creating a triple therapy regimen.
Beyond medication, non-pharmacological interventions are also tailored to the severity group. Pulmonary rehabilitation, a comprehensive program of exercise, education, and psychological support, is an important strategy for all symptomatic patients, especially those in Groups B and E. Smoking cessation counseling remains a fundamental part of the management plan for all individuals with COPD.