Sputum eosinophilia predicted emergency visits in asthma but not health service use in COPD

Design

Retrospective cohort linked to Ontario health administrative data

Population

4,821 patients with asthma (3,714) or COPD (1,107) at a tertiary airway clinic

Primary outcome

Hospitalisations, emergency and physician visits after baseline sputum count

Effect

Asthma eosinophils 3 to 15%: RR 1.92 (1.49 to 2.47) for asthma ED visits; COPD neutrophilia: RR 1.71 (1.11 to 2.64) for hospitalisation

Researchers linked sputum cell counts from a Canadian tertiary airway clinic to provincial health records over more than a decade.

In asthma, eosinophilic airway inflammation was associated with more emergency and asthma-related care. In COPD it was not; instead, neutrophilic inflammation was linked to more hospital admissions.

The findings support sputum inflammometry in difficult asthma and caution against treating COPD as eosinophilic asthma by another name. Induced sputum is not widely available in India, but the asthma-COPD distinction still applies when interpreting blood eosinophils.

• In asthma, sputum eosinophils above 3% were linked to about twice the rate of asthma emergency visits.
• The 3 to 15% and above 15% groups had similar risk.
• In COPD, sputum eosinophils were not associated with hospital or emergency use.
• In COPD, high sputum neutrophils were linked to more all-cause hospitalisations (RR 1.71).
• Blood eosinophils are the practical proxy where sputum testing is not available.

Why it matters

Eosinophil-guided treatment is extended from asthma to COPD by analogy, and this cohort suggests the two diseases behave differently.

Don't overread it

This is an observational cohort from one tertiary clinic, with sputum measured once at baseline.

The statistics, in plain English

A rate ratio of 1.92 means almost twice as many emergency visits. The baseline sputum was a single measurement, so changes over time are not captured.

Read the rest in the app

You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.

Get Daily Doctor — free

Scan to keep reading on your phone. No account needed to start.