Chronic Obstructive Pulmonary Disease (COPD), which includes emphysema and chronic bronchitis, is a progressive condition causing persistent airflow limitation and increasingly difficult breathing. It is a major global cause of death and disability. Measuring COPD severity is complex, involving both physical lung damage and the daily impact of symptoms. A standardized system is necessary for consistent diagnosis and effective long-term management.
The Purpose of the GOLD System
The Global Initiative for Chronic Obstructive Lung Disease (GOLD) provides the internationally recognized framework for COPD diagnosis, management, and prevention. Established through a collaboration of health organizations, the GOLD guidelines are regularly updated to incorporate the latest scientific evidence. This standardized approach ensures healthcare professionals worldwide use the same objective criteria when assessing patients.
A consistent classification helps predict the disease’s course and guides treatment decisions, including medication choices. The GOLD system acknowledges that COPD is not uniform; two patients with similar lung damage can have different symptoms and risks. To address this complexity, the system uses two distinct axes: one focused on physiological lung damage and another on the patient’s current symptoms and future risk of flare-ups.
Defining Severity: GOLD Stages 1 through 4
The numerical staging system of GOLD defines four grades of airflow limitation. These stages, numbered 1 through 4, are based exclusively on the results of spirometry, a breathing test measuring the forced expiratory volume in one second (FEV1). Spirometry measures the total volume of air exhaled, the forced vital capacity (FVC), and the volume exhaled in the first second (FEV1).
The key diagnostic factor for COPD is a post-bronchodilator FEV1/FVC ratio of less than 0.70, which confirms persistent airflow obstruction. Once this obstruction is confirmed, the severity is graded based on the FEV1 value compared to what is predicted for a healthy person of the same age, sex, and height. Stage 1 is categorized as Mild, where the FEV1 is 80% or greater than the predicted normal value.
Stage 2 is considered Moderate, defined by an FEV1 percentage between 50% and 79% of the predicted value. Stage 3 represents Severe airflow limitation, where the FEV1 falls into the range of 30% to 49% of the predicted value. The most severe limitation is Stage 4, or Very Severe, which is diagnosed when the FEV1 is less than 30% of the predicted value. These numerical stages reflect the anatomical and physiological damage within the lungs.
Assessing Risk: The ABCD Patient Groups
In addition to the four numerical stages, the GOLD system uses a separate classification matrix, known as the patient groups, to assess the clinical impact of the disease. This grouping focuses on two factors unrelated to FEV1: the current burden of symptoms and the risk of future exacerbations. Symptoms are evaluated using validated tools, such as the COPD Assessment Test (CAT) (score of 10 or greater indicates more symptoms) or the modified Medical Research Council (mMRC) Dyspnea Scale (score of 2 or greater indicates more breathlessness).
The risk of exacerbation is determined by a patient’s history over the previous year. A low-risk patient is defined as having had either zero or only one moderate exacerbation that did not require hospitalization. A high-risk patient is one who has had two or more moderate exacerbations or at least one severe exacerbation requiring a hospital admission. The original ABCD matrix combined these factors into four groups to guide initial pharmacological treatment.
Group A includes patients with a low symptom burden and a low exacerbation risk. Group B patients have a high symptom burden but fall into the low-risk category. Groups C and D were the high-risk categories, with C having low symptoms/high risk and D having both high symptoms and high risk. Recent GOLD updates recognized the importance of exacerbations, leading to a modification where the former high-risk groups C and D are often combined into a single Group E (for Exacerbations) in treatment recommendations.
Applying the Combined Classification
The final step for healthcare providers is to use both the spirometry-based numerical stage and the symptom/exacerbation group to classify the patient. A patient is never simply “Stage 3” or “Group D” but is instead classified by a combination, such as GOLD Stage 2, Group B. This combined classification provides a comprehensive profile of the patient’s condition, integrating the physiological damage with the clinical consequences.
For instance, a patient might have severe airflow limitation (Stage 3) but experience few symptoms and infrequent exacerbations (Group A). Conversely, a patient with only moderate airflow limitation (Stage 2) could have a high symptom burden and frequent exacerbations, placing them in Group E. This dual system allows for tailored management strategies: the numerical stage informs prognosis and non-pharmacological interventions like pulmonary rehabilitation, while the letter group primarily determines the choice of pharmacological treatment. Patients classified into higher numerical stages and higher risk groups, such as Group E, require more aggressive and complex management to control symptoms and prevent future flare-ups.