CA 15 - 3 in screening for systemic autoimmune rheumatic disease associated interstitial lung disease: a single center cross-sectional study.

Introduction: The natural course of interstitial lung disease (ILD) in patients with systemic autoimmune rheumatic diseases (SARD) varies significantly and is linked to considerable morbidity and mortality. Therefore, effective screening is crucial for early detection of SARD-ILD. Biomarkers associated with mucin 1, Krebs von den Lungen-6 (KL-6) and carbohydrate antigen 15-3 (CA 15-3), are increased in various ILD. This study aimed to assess the diagnostic accuracy of the serum biomarker CA 15-3 as a potential screening tool for ILD in patients newly diagnosed with SARD.

Methods: Conducted as a single-center cross-sectional study, the research included newly diagnosed SARD patients consecutively examined for ILD according to the algorithm. All included patients underwent chest high-resolution CT scans (HRCT), and serum levels of CA 15-3, KL-6, and lactate dehydrogenase (LDH) were measured and correlated with other variables associated with possible ILD presence.

Results: Serum biomarker levels, specifically CA 15-3 and LDH, are significantly higher in ILD-positive patients (P<0.001 for both). An inverse relationship is observed between higher FVC values and lower CA 15-3 levels (Rho=-0.291, P=0.007). Similarly, higher DLCO values are associated with lower CA 15-3 levels (Rho=-0.317, P=0.003). Our findings revealed that elevated CA 15-3 levels are positively correlated with higher levels of KL-6 (Rho=0.268, P=0.01) and LDH (Rho=0.227, P=0.04). With a cut-off value of 24 U/mL, CA 15-3 showed the highest sensitivity and specificity (AUC=0.807, specificity=95.7%, sensitivity=71.1%). CA 15-3 emerged as the most significant predictor of a positive HRCT finding, accurately classifying 83% of cases.

Conclusion: These results suggest that CA 15-3 shows promise as a valuable serum biomarker for screening SARD patients for ILD in routine clinical practice.