The diagnostic utility of BAL in children with interstitial lung disease

<bold>Background:</bold> Childhood interstitial lung disease (ChILD) has a high morbidity and mortality. Diagnosis usually involves genetic testing. If genetic testing is inconclusive, this is often followed by a bronchoscopy with bronchoalveolar lavage (BAL),without a lung biopsy (LB). The diagnostic value of bronchoscopy, among ruling out structural abnormalities or infections, is unclear. <bold>Aim:</bold> To compare the diagnostic value of BAL in patients with confirmed interstitial lung disease on lung histology. <bold>Methods:</bold> A prospective monocentric study of children undergoing concurrent BAL and LB for suspected ChILD between December 2022 and September 2023. <bold>Results:</bold> 45 patients (10 years,IQR:2.9;13.2) were included. BAL fluid (BALF) showed lymphocytic and granulocytic inflammation in 11 (24%) and 28 (62%) patients respectively. Lipid-laden macrophages were seen in 14 (31%) and hemosiderin-laden macrophages (HLM) in 22 (48%) patients. All LBs provided a diagnosis for ChILD, however none showed evidence of ChILD related to recurrent aspiration. 8 (18%) patients had LB confirmed diffuse alveolar haemorrhage (DAH), this correlated with 7 patients who had elevated HLM.15 (33%) children with elevated HLM in BALF did not demonstrate DAH on LB. 19/44 (43%) and 15/43 (35%) had confirmed viral and bacterial organisms in BALF respectively. No histological evidence of ChILD related to infection were noted on LB. BALF correlated with DAH histology in 16% of cases, while the remaining 84% of patients required a LB for a definitive diagnosis. <bold>Conclusion:</bold> BALF alone was neither sensitive nor specific for diagnosing ChILD. However, it is useful for detecting or excluding concurrent infections. The presence of HLM in BALF is not always diagnostic for DAH.