Follow-up of serum KL-6 lung fibrosis biomarker levels in 173 patients with systemic sclerosis

Objective. A single-centre retrospective longitudinal study to investigate the predictive value of KL-6 serum levels for the outcome of interstitial lung fibrosis in a large systemic sclerosis (SSc) patient cohort. Methods. ELISA tests for the mucin like glycoprotein KL-6 were performed in sera of 173 SSc patients. The clinical and laboratory data were evaluated by a standardised protocol of chest x-ray, lung function tests, echocardiography and high-resolution computed tomography. 158 patients were 29 22 months later reinvestigated, 9 patients (2 lcSSc, 7 dcSSc) died from SSc-related causes, and 6 patients were lost to follow-up. Results. Serum titer of KL-6 was negatively correlated with lung function parameters, independent of the time of investigation. There was a significantly higher probability of death among patients with high level of baseline KL-6. There was no statistically significant difference in the deterioration and improvement rates between groups with normal and elevated KL-6 level at study entry, even in patients in early phase of disease (disease duration <3 years). Serum levels of KL-6 significantly decreased in patients receiving cyclophosphamide treatment in spite of the fact that the spirometry results (FVC and DLCO) did not show a significant change. Conclusion. KL-6 can be used as a lung fibrosis severity marker, but its role as a marker for disease activity is questionable. Furthermore, following cyclophosphamide treatment serum KL-6 levels may decrease independently of the lung function parameters.