Protein expression of airway biomarkers in paediatric lower respiratory tract infection (LRTI)

<bold>Introduction:</bold> Antibiotics are overused in paediatric LRTI, as viral infection is often clinically indistinguishable from bacterial infection. Four potential biomarkers determined from a discovery group, relevant animal models and literature review, were assessed as a potential solution. Method The expression of haptoglobin (HP), angiotensinogen (AGT), PIGR and Annexin A2 (AX2) in the lower (LRT) and upper respiratory tract (URT) of children with and without LRTI was determined. Simultaneous paired non-bronchoscopic LRT lavage & nasopharyngeal swabs were obtained from intubated patients. An expert panel assigned LRTI cases as likely bacterial or viral. Control children were undergoing routine surgery. Biomarkers measured by ELISA. <bold>Results:</bold> 13 paired LRT & URT samples obtained. 6 control, with 3 assigned bacterial and 4 viral. Biomarker values all pg/ml. LRT and URT results aligned for HP and AX2. HP levels were higher in bacterial (LRT:6409;URT:8267) vs viral (LRT:5217; URT:6846) and controls (LRT:334;URT:6819). AX2 levels were higher in controls (LRT:9.7;URT:10.4) compared to bacterial (LRT:9.6;URT:9.6) and viral (LRT:9.2;URT:8.4). Misalignment of LRT and URT was observed for AGT and PIGR. AGT LRT levels were higher in bacterial (8108) vs viral (1219) and control (480), but in URT were higher in viral (7006) compared to bacterial (6651) and control (1053). PIGR LRT levels were similar in bacterial (20.9) and viral (20.0) groups with both higher than control (12.4), but in URT levels were higher in viral (25.4) compared to bacterial group (19.1) and controls (0.9). <bold>Conclusions:</bold> HP and AX2 measured in the URT may represent LRT inflammation. This should be explored further in larger samples.