Association between exhaled carbon monoxide and asthma outcomes in Peruvian children

Background: Asthma prevalence continues to increase in low and middle-income countries, presenting challenges in assessing asthma control in resource-poor settings. Previous studies suggest that exhaled carbon monoxide (eCO) is higher with asthma severity and lower with treatment. We hypothesized that eCO levels may be elevated in children with asthma, particularly in children with partially controlled or uncontrolled asthma in a low-resource setting in Lima, Peru. Methods: We compared average eCO levels between 248 children with asthma and 221 healthy controls as well as the odds of asthma by eCO quartiles (0–1, 2, 3, and ≥4 ppm) using multivariable linear and logistic regression. eCO quartiles were also used to compare the odds of partially controlled or uncontrolled asthma (score ≤19 on the Asthma Control Test) in a multivariable logistic regression model. Findings: Average adjusted eCO level was 0.56 ppm (95% CI 0.07–1.05) higher in children with asthma. The adjusted odds of asthma were 1.22 (95% CI 0.75–1.97), 1.46 (0.81–2.63), and 1.76 (0.96–3.23) in the second, third, and fourth eCO quartiles compared to the first eCO quartile, respectively. Among children with asthma, the adjusted odds of partially controlled or uncontrolled asthma in those in the second, third, and fourth eCO quartiles, compared to the first, were 1.61 (95% CI 0.74–3.48), 3.66 (95% CI 1.51–8.87), and 2.50 (95% CI 1.06–5.90), respectively. Interpretation: eCO may serve as an inexpensive biomarker for asthma control, particularly in low-resource settings.