Can a Peripheral Blood Marker for Airway Neutrophilia Be Identified in Children with Bronchiectasis?

Background: Airway bacterial infection and inflammation are often present in children with bronchiectasis. Systemic inflammation has also been reported. Currently, there are no data on the association between systemic inflammatory markers with airway pathogens or neutrophilia in children with bronchiectasis. We aimed to define the bronchoalveolar lavage (BAL) pathogens (bacteria and viruses), and cytology in children with bronchiectasis and to explore any association between peripheral inflammatory markers and airway neutrophilia. Methods: Participants numbering 402, aged <18 years, with peripheral blood and BAL results within 3 months of diagnosis of bronchiectasis were included. Blood and BAL results were reviewed and analysed for possible associations. Results: Of 355 children (88.31%), cultured bacteria from BAL and Haemophilus influenzae (n = 185) were the most frequent. A virus was identified in 131 (32.59%). Adenovirus (n = 69) was most common. Children numbering 279 (69.40%) had airway neutrophilia (neutrophils > 15%) which was associated with the presence of H. influenzae (OR 2.03 95% CI 1.31-3.15, p = 0.002), S. pneumonia 2.41 (95% CI 1.36-4.29, p = 0.003), and Adenovirus (OR 2.06 95% CI 1.06-4.04, p = 0.033). Airway neutrophilia was associated with raised CRP (OR 2.26 95% CI 1.14-4.49, p = 0.019), but there were no other systemic inflammatory markers including monocyte/lymphocyte ratio, neutrophil/lymphocyte ratio, platelet/lymphocyte ratio, and platelet/mean platelet volume ratio. Conclusions: In children, there is an association between airway neutrophilia and raised CRP in bronchiectasis, but not with other peripheral inflammatory markers. There is a need to identify non-invasive inflammatory markers in children with bronchiectasis.