[The diagnostic value of serum KL-6 in connective tissue disease associated interstitial lung disease]

Objective: To evaluate the diagnostic value of the serum Krebs von den Lungen-6 (KL-6) for the interstitial lung disease associated with connective tissue diseases (CTD-ILD). Methods: 84 patients with CTD-ILD (CTD-ILD group) and 91 patients with connective tissue disease (CTD group) who visited the department of rheumatology and immunology of People's Hospital of Xinjiang Uygur Autonomous Region between January, 2016 and December, 2017 were included. Serum KL-6 levels were measured by commercially available enzyme linked immunosorbent assay (ELISA) kits. Results: The significantly higher levels of KL-6 were determined in the CTD-ILD group than CTD group [1 239 (577, 2 094) vs 152 (89, 280) U/ml] (P<0.001). The optimal cutoff value of serum KL-6 for diagnosis of CTD-ILD was 402 U/ml, and the sensitivity and specificity were 82.1% and 86.8%, respectively. Area Under the Curve (AUC) was 0.905. Logistic regression analysis revealed that elevated KL-6 and decreased Carbon monoxide diffusion capacity were independently correlated with the occurrence of CTD-ILD, the decreased of DLcoSB% (OR=0.928, 95%CI: 0.891-0.968) and increase of KL-6 level (OR=1.005, 95%CI: 1.003-1.007) was the independent risk factor for the occurrence of ILD. Conclusion: The serum KL-6 is an important biomarker for the diagnosis of CTD-ILD and when the level of KL-6 is increased, the ILD should be alert.