Diagnostic Performance of CLEIA Versus FEIA for KL‐6 Peripheral and Alveolar Concentrations in Fibrotic Interstitial Lung Diseases: A Multicentre Study

ABSTRACT Background Interstitial lung diseases (ILD) is a group of lung disorders characterized by interstitial lung thickening due to inflammatory and fibrotic processes. Krebs von den Lungen‐6 (KL‐6) is a molecule secreted by damaged type II alveolar pneumocytes in the alveolar space. The goal of the present study was to compare two detection methods of KL‐6 in both bronchoalveolar lavage (BAL) and serum from ILD patients at the moment of diagnosis. Methods Patients with suspicious of ILD and followed at two Italian referral centres for rare lung diseases were included in the study. BAL fluid and serum were collected and analysed by chemiluminescent enzyme immunoassay (CLEIA) and fluorescent enzyme immunoassay (FEIA) methods provided by Tosoh Biosciences. Results A total of 158 (mean age ± standard deviation, 61.5 ± 13.7, 65 females) patients were enrolled. A total of, 36 had diagnosis of idiopathic pulmonary fibrosis (IPF), 74 sarcoidosis, 15 connective tissue disease‐ILD (CTD‐ILD) and 33 other ILD. Diagnostic agreement between two methods was demonstrated for both BAL ( r = 0.707, p < 0.0001) and serum ( r = 0.816, p < 0.0001). BAL KL‐6 values were lower than serum ( p < 0.0001). IPF patients had higher serum KL‐6 concentration than other ILDs ( p = 0.0294), while BAL KL‐6 values were lower in IPF than in non‐IPF ( p = 0.0023). Conclusion This study explored KL‐6 concentrations through the CLEIA method in serum and BAL of patients with various ILDs, showing significant differences of biomarkers concentrations between IPF and other non‐IPF ILDs. Our findings are promising as they provided further knowledge concerning KL‐6 expression across different ILDs and may suggest its utility in differential diagnosis.