Serum KL-6 as a diagnostic and prognostic biomarker in inflammatory myopathies-associated interstitial lung disease: A single-centre prospective cohort study

BACKGROUND AND OBJECTIVE: Interstitial lung disease (ILD) is the leading cause of mortality in inflammatory myopathies (IIM). We evaluated serum Krebs von den Lungen-6 (KL-6) as a diagnostic and prognostic biomarker for IIM-associated ILD. MATERIAL AND METHODS: Single-centre prospective cohort of 54 consecutive adults with IIM (2023-2025). Baseline serum KL-6 (chemiluminescent immunoassay) was related to HRCT-confirmed ILD by bootstrap ROC analysis; associations with autoantibodies, cumulative immunosuppressive burden and clinical outcomes were explored. RESULTS: ILD was present in 28/54 (51.9%). KL-6 was higher with ILD (565 vs 276U/mL; p<.001); AUC 0.889, threshold 450U/mL (sensitivity 78.6%, specificity 92.3%), reaching AUC 1.000 within 90 days of HRCT. All three deaths occurred in anti-Ro52-positive patients (3/17 vs 0/37; p=.027). Baseline KL-6 predicted hospitalisation, ILD-related hospitalisation and radiologic progression. CONCLUSIONS: Serum KL-6 shows high diagnostic accuracy for IIM-associated ILD and tracks adverse outcomes. These hypothesis-generating findings warrant validation in larger multicentre cohorts.