Elevated serum Krebs von den Lungen-6 in primary Sjögren syndrome: a marker of lung fibrosis and severity of the disease

Abstract Background: To assess the diagnosis significance of the serum Krebs von den Lungen-6 (KL-6) for the interstitial lung disease (ILD) related to primary Sjögren syndrome(pSS-ILD) Methods: An overall 79 pSS-ILD sufferers and 71 pSS sufferers from our hospital between Jan 2015 and May 2021 were enrolled. The measuring of serum KL-6, lung function testing, and high-resolution computed tomography (HRCT) completed simultaneously were studied. Serum KL-6 concentrations were measured with chemiluminescent enzyme immunoassay (CLEIA).Correlative analyses and receiver-operator characteristic (ROC) analyses were completed to identify the value of the aforesaid measuring results.Results: The remarkably higher contents of KL-6 were identified in pSS-ILD patients in contrast to pSS patients [795.1±725.3U/ml vs 198.6±77.5U/ml] (P＜0.001). The optimum threshold of serum KL-6 for the diagnoses of ILD was 276.5 U/ml, and the sensitivity and specificity were 87.3% and 88.7%, respectively. The area under the curve (AUC) was 0.919 and the logistic regression analysis revealed that elevated KL-6 and decreased carbon monoxide diffusion capacity were independently correlated with the occurrence of pSS-ILD, and the increase of KL-6 levels was an independent risky factor for the occurrence of ILD (OR=1.019, 95%CI: 1.010~1.029). Conclusion: The serum KL-6 is a vital marker for the diagnoses of pSS-ILD, and when the KL-6 content is elevated, there is an underlying risk of ILD.