The joint statement from the Global Initiative for Chronic Obstructive Lung Disease (GOLD) and the Global Lung Function Initiative (GLI) marks a definitive conclusion to three decades of scientific polemics surrounding spirometry standards.
This document finalizes the rules for using spirometry—the recognized “gold standard” for detecting airway obstruction—for clinicians. Establishing an accurate diagnosis or rejection of COPD is the prerequisite for developing more effective patient treatment strategies. COPD remains a leading cause of morbidity and mortality worldwide, affecting millions through progressive lung damage.
The Heterogeneity of COPD
Uncertainty in COPD diagnosis is often linked to the disease’s pronounced heterogeneity, measurement errors, and biological variability. Because lung function impairment exists on a continuous spectrum rather than at sharp thresholds, any diagnostic limit struggles to perfectly separate normal variation from real pathology.
In real-world practice, among smokers over the age of 40, the discrepancy between the fixed 0.7 ratio and the Lower Limit of Normal (LLN) affects only a small portion of cases (approximately 8–18%). In “gray zones,” where the ratio fluctuates between 0.6 and 0.8, a final diagnostic decision should never be made based on a single test. In these instances, repeating the test or determining the Slow Vital Capacity (SVC) is an essential requirement.
Besides the technical side, the physical state of the patient also has an influence on the diagnosis. For example, obesity, through the way of the proportional reduction of lung volumes (FVC), might determine the false normalization of the ratio and the masking of the obstruction. All of this indicates that relying only on digital data is insufficient and the clinician must always produce a critical analysis of the patient’s individual state.
The Debate: Fixed Ratio vs. Lower Limit of Normal (LLN)
The primary purpose of spirometry in COPD is to identify airflow limitation based on the reduction of the ratio. Two main clinical approaches have historically competed:
The GOLD Approach (Fixed Ratio < 0.7): Since 2001, GOLD has advocated for a simplified model where obstruction is defined as a post-bronchodilator ratio of less than 0.7. Its strength lies in its simplicity and independence from reference equations, facilitating easier screening in risk groups.
The GLI/ATS/ERS Approach (LLN): This method calculates a threshold individually based on the patient’s age, sex, and height, derived from healthy population data. Proponents argue that lung function naturally declines with age; thus, a fixed 0.7 ratio may underdiagnose young people and overdiagnose the elderly.
Despite theoretical differences, in symptomatic patients, both methods are clinically valuable. In elderly smokers, the fixed 0.7 ratio often reveals pathological changes (associated with respiratory symptoms and gas exchange disturbances) that the LLN might miss, identifying clinically significant disease earlier.
Quality Standards in Spirometry
Diagnostic thresholds are irrelevant if the quality of the spirometry does not meet standards. To obtain a valid result:
The patient must perform a maximum, forceful expiration from Total Lung Capacity (TLC) to a flow plateau (full emptying).
The test must be free of artifacts such as coughing or early termination.
Medical personnel must provide correct instructions and continuous technical monitoring.
Distinguishing Bronchodilatory Response and Reversibility
Understanding the difference existing between the bronchodilatory response and the reversibility of the obstruction is decisive in the process of clinical diagnostics. In many cases, these two terms are mixed into each other, which causes a certain misunderstanding during the interpretation of the diagnosis. The bronchodilatory response only shows how much specific indicators of lung function improved, for example or , after taking the preparation. This is a purely digital increase, which points to the reactivity of the airways.
In contrast to this, the reversibility of the obstruction represents a much more strict critical limit. It implies a condition when the ratio normalizes under the influence of the preparation and equalizes with the established norm (0.7 or LLN). The majority of patients diseased with COPD indeed exhibit a positive clinical response to the bronchodilator, although they still cannot achieve the full elimination of the obstruction, that is, reversibility, due to the structural damage of the airways.
The use of the bronchodilatory test is a necessary stage for the purpose of excluding asthma and for confirming the accuracy of the obtained data. It is true that the digital figures after the use of the preparation create a more solid and stable diagnostic basis, although the initial, basal data also still maintain their functional validity. Accordingly, while making a clinical decision, the doctor must consider the results of both phases in a complex way.
Classification of the Severity of Obstruction
While determining the severity of the obstruction, various organizations rely on different methodology. For example, GOLD uses the predicted percentage indicator, while ATS/ERS assign preference to Z-scores (z-scores). The latter represent data standardized according to the patient’s age, height, and sex. It is true that Z-scores reflect shortness of breath and the risk of hospitalization more accurately, although the absolute indicator of still surpasses both of them in predicting mortality.
One of the main difficulties while evaluating lung function represents historically established racial coefficients. Over the years, it was considered that representatives of different ethnicities have different natural lung volumes, which often causes a real pathology to be considered as a norm or the involuntary reinforcement of social inequality. To eliminate this flaw, since 2022 modern medicine has been trying to move to GLI’s racially neutral, unified global standard.
Despite this step taken forward, a unified model still cannot fully encompass the specific biological peculiarities of different regions. The problem is also complicated by the fact that lung volume is dependent not so much on race, but on individual body proportions, specifically, the size of the chest. Since measuring the exact parameters of the chest represents a great difficulty in practice, doctors often use the determination of height in a sitting position, although this method also gives only approximate data.
In the final analysis, while evaluating lung function, the main orientation represents not only digital marks, but the validity of the obtained data. High-quality spirometry and an in-depth analysis of the patient’s symptoms reduce the risk of a wrong diagnosis to a minimum. While the combination of these processes is the prerequisite for developing a personalized therapeutic strategy and for improving the quality of the patient’s life.
