Lung ultrasound B-lines and serum KL-6 in the management of connective tissue disease-associated interstitial lung disease

Background and objectives: Interstitial lung disease (ILD) is a major cause of morbidity and mortality in patients with connective tissue diseases (CTDs). Early diagnosis, appropriate intervention, and close monitoring are critical to mitigate the progression of CTD-ILD. Lung ultrasound (LUS) B-lines and serum Krebs von den Lungen-6 (KL-6) have emerged as promising, non-invasive, and radiation-free biomarkers for ILD. This single-center retrospective study aimed to evaluate the combined diagnostic and assessment value of B-lines and KL-6 in patients with CTD-ILD.

Methods

A total of 226 consecutive patients with CTD who underwent high resolution computed tomography (HRCT), LUS and serum KL-6 testing within a one-month interval were retrospectively enrolled. Based on HRCT findings, patients were classified into ILD and non-ILD groups. Those with ILD were further subdivided into fibrotic ILD (F-ILD) and non-fibrotic ILD (NF-ILD) according to radiographic patterns. LUS was performed across 50 scanning sites, and the total number of B-lines was calculated as a B-lines number. Correlations between B-lines number, KL-6 level, and HRCT Warrick score were analyzed. The diagnostic accuracy of LUS B-lines and KL-6, individually and in combination, for detecting ILD and F-ILD was determined using receiver operating characteristic (ROC) curve analysis. The ability of B-lines and KL-6 to discriminate ILD severity based on the HRCT Warrick score was assessed.