In a 119,000-person global cohort, 89% of spirometry-defined COPD was undiagnosed

Chronic obstructive pulmonary disease (COPD) is defined by airflow obstruction that shows up on spirometry, the simple breathing test that measures how much and how fast a person can exhale. A large multinational cohort analysis published in The Lancet Global Health on 2 October asks a question that has rarely been answered outside wealthy countries: of the people whose lungs meet the spirometric definition, how many have actually been diagnosed — and what happens to those who have not [s1].

The study

The analysis draws on the Prospective Urban Rural Epidemiology (PURE) study, which systematically collected spirometry from adults aged 35 to 70 in urban and rural communities across 25 high-income, middle-income, and low-income countries [s1]. Participants with airflow obstruction on spirometry who also had a physician diagnosis of an airway disease were classed as having diagnosed COPD; those with the same spirometry result but no physician diagnosis were classed as underdiagnosed; and those with normal spirometry and no known airway disease were classed as having no COPD [s1]. Baseline details came from standardised interviews, and follow-up data on survival and clinical events were collected every three years [s1]. That prospective design is what lets PURE go beyond a prevalence snapshot: by tracking the diagnosed, the underdiagnosed, and the no-COPD groups forward in time, it can test whether cases that slipped past the health system carry worse outcomes than cases that were caught — the practical question behind any argument for wider screening [s1].

Between 11 July 2002 and 28 July 2025, the investigators gathered technically acceptable spirometry from 119,252 participants, with a baseline median age of 51 (IQR 43–59); 71,039 (59.6%) were female and 48,213 (40.4%) male [s1].

What the numbers say

The prevalence of airflow obstruction was 9.5% (11,306 of 119,252 participants) [s1]. The striking finding is how little of it had been recognised: 89.2% of those cases — 10,080 of 11,306 — were underdiagnosed, meaning the person met the breathing-test definition of COPD but had never received a physician diagnosis of an airway disease [s1].

The picture varied sharply by region. Airflow obstruction ranged from 6.1% (521 of 8,601) in southeast Asia to 20.4% (785 of 3,846) in sub-Saharan Africa [s1]. It was more common in low-income and middle-income countries, at 9.8% (10,120 of 103,758), than in high-income countries, at 7.7% (1,186 of 15,494) [s1]. Underdiagnosis was not confined to poorer settings — it was the dominant pattern everywhere — but it reached 90.7% in the lower-income group, the paper reports [s1].

Why it matters

The clinical weight of these figures comes from what COPD does when it goes untreated. The World Health Organization lists COPD as the third leading cause of death worldwide, responsible for 3.4 million deaths in 2023, roughly 6% of all deaths globally [s2]. Nearly 90% of COPD deaths in people under 70 occur in low- and middle-income countries — the same settings where PURE found both the highest prevalence and the highest rate of missed diagnosis [s1][s2]. It is also the seventh leading cause of poor health worldwide as measured by disability-adjusted life-years [s2].

The risk factors differ by setting in a way that compounds the diagnostic gap. The WHO notes that tobacco smoking accounts for over 70% of COPD cases in high-income countries but only 30–40% in low- and middle-income countries, where household air pollution is a major driver [s2]. Where smoking is not the obvious culprit, clinicians may be less primed to suspect COPD, and spirometry — the only way to confirm it — is often unavailable, which is consistent with the near-universal underdiagnosis PURE documented [s1][s2]. The gap is self-reinforcing: without routine spirometry, obstruction is missed; without a diagnosis, patients are not offered inhalers, pulmonary rehabilitation, or advice to reduce the exposures driving the disease, and the condition progresses unchecked toward the deaths the WHO counts [s1][s2].

Two cautions apply. First, a spirometry-defined case is not identical to a clinical diagnosis: obstruction on a single test can reflect other conditions, and not everyone who meets the threshold has symptomatic disease, so the underdiagnosis figure describes a measurement gap rather than a count of people in need of treatment that day [s1]. Second, PURE recruited from specific urban and rural communities and is not a formal global prevalence survey, so the regional percentages describe its cohort rather than whole countries [s1]. Even with those limits, the central result is hard to dismiss: across 25 countries and more than 119,000 people, the large majority of spirometry-defined COPD was invisible to the health system, and it was most invisible where the disease was most common [s1].

Sources

• [s1] The burden and long-term outcomes of diagnosed and underdiagnosed COPD across diverse communities from high-income, middle-income, and low-income countries: the PURE study. The Lancet Global Health. https://doi.org/10.1016/j.langlo.2026.104055
• [s2] Chronic obstructive pulmonary disease (COPD) (fact sheet). World Health Organization. https://www.who.int/news-room/fact-sheets/detail/chronic-obstructive-pulmonary-disease-(copd)