Three or more CT mucus plugs predicted exacerbations and new COPD in people with normal spirometry

Design

Prospective community-based cohort, 3-year follow-up

Population

1,939 Chinese adults (847 COPD, 1,092 preserved spirometry) with baseline CT

Primary outcome

Exacerbations, lung function decline and incident spirometric COPD

Effect

≥3 plugs with preserved spirometry: exacerbation RR 1.42 (1.11–1.81); new COPD 18.2% vs 7.6%, RR 1.71 (1.05–2.78)

This prospective community cohort in China enrolled 1,939 adults — 847 with COPD and 1,092 with preserved spirometry — who had baseline spirometry and chest CT; 89% completed three years of follow-up. Mucus plugs were counted by the number of lung segments affected.

In people with preserved spirometry, 1–2 plugged segments (RR 1.22) and three or more (RR 1.42) were associated with more exacerbations. Three or more plugs were associated with developing spirometric COPD (18.2% vs 7.6%, RR 1.71, 95% CI 1.05–2.78) and faster FEV1/FVC decline. In COPD, including mild and asymptomatic disease, three or more plugs were associated with more moderate-to-severe exacerbations.

Mucus plugs are already known to predict poor outcomes in moderate-to-severe COPD. This study extends that to people whose spirometry is still normal, suggesting that plugs mark airway disease before it shows on a spirometer. It is observational and from one population, but CT is increasingly done for other reasons, so the finding is often already available.

• Look for mucus plugs on any chest CT in a smoker or someone with respiratory symptoms, even if spirometry is normal.
• Three or more plugged segments with normal spirometry warrant follow-up spirometry and smoking cessation support.
• Ask radiologists to report mucus plugs specifically.
• In established COPD, plugs identify patients at higher exacerbation risk who need an optimised maintenance plan.

Why it matters

It gives a way to spot early airway disease that spirometry misses, in an era of widespread CT.

Don't overread it

Observational association in one Chinese community cohort — it does not show that treating plugs changes outcomes.

The statistics, in plain English

An RR of 1.71 for new COPD has a confidence interval of 1.05 to 2.78 — a real but imprecisely sized association.

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