Exhaled nitric oxide and urinary EPX levels in infants: a pilot study

Higher exhaled nitric oxide at 6 weeks of age is associated with less bronchiolitis and wheeze in the first 12 months of age

BACKGROUND

Nitric oxide in exhaled air (eNO) is used as a marker of type 2 immune response-induced airway inflammation. We aimed to investigate the association between eNO and bronchiolitis incidence and respiratory symptoms in infancy, and its correlation with eosinophil protein X (EPX).

METHODS

We followed up infants at 6 weeks of age born to mothers with asthma in pregnancy and measured eNO during natural sleep using a rapid response chemiluminescense analyser (CLD88; EcoMedics), collecting at least 100 breaths, interpolated for an expiratory flow of 50 mL/s. EPX normalised to creatinine was measured in urine samples (uEPX/c). A standardised questionnaire was used to measure symptoms in first year of life. Associations were investigated using multiple linear regression and robust Poisson regression models.

RESULTS

eNO levels were obtained in 184 infants, of whom 125/184 (68%) had 12 months questionnaire data available and 51/184 (28%) had uEPX/c measured. Higher eNO was associated with less respiratory symptoms during the first 6 weeks of life (n=184, ß-coefficient: -0.49, 95% CI -0.95 to -0.04, p=0.035). eNO was negatively associated with uEPX/c (ß-coefficient: -0.004, 95% CI -0.008 to -0.001, p=0.021). Risk incidence of bronchiolitis, wheeze, cold or influenza illness and short-acting beta-agonist use significantly decreased by 18%-24% for every unit increase in eNO ppb.

CONCLUSION

Higher eNO levels at 6 weeks of age may be a surrogate for an altered immune response that is associated with less respiratory symptoms in the first year of life.

Eosinophil protein X and childhood asthma: A systematic review and meta-analysis

Background: There are no reference guidelines for health care providers regarding appropriate use and interpretation of urine eosinophil protein X (u‐EPX) in clinical practice. Currently, there are no clear‐cut clinical or laboratory parameters to diagnose asthma in young children. Objective: In this study, we (1) systematically reviewed and qualitatively appraised the epidemiological evidence to determine diagnostic u‐EPX cut points for pediatric asthma, and (2) performed a meta‐analysis to provide u‐EPX estimates for diagnosing pediatric asthma. Methods: Research articles in literature were identified from PubMed/Medline and Web of Science databases from 1966 to August 2015. Children <18 years of age were included. Both serum and urine EPX were included. Twenty‐seven studies met the inclusion criteria for the systematic review and nine studies for the meta‐analysis. Details regarding EPX analyses, treatment efficacy, and outcomes were assessed. For meta‐analyses, effect estimates were abstracted using standardized means. Results: Over 70% of studies found a significant relationship between u‐EPX and childhood asthma. There was 1.94 times higher standardized means of u‐EPX among acute asthmatics compared to healthy controls (confidence interval [CI]: 1.67–2.22). Similarly, the difference in standardized means between asymptomatic asthmatics and healthy controls was 1.58 times higher (CI: 1.27–1.88). Conclusions and Clinical Relevance: Despite differences in sample sizes, EPX processing and measurement, and ages of children, a consistent trend of higher EPX levels with childhood asthma was revealed.