Clinical relevance of the serial measurement of krebs von den lungen-6 levels in patients with systemic sclerosis-associated interstitial lung disease

Krebs von den Lungen-6 (KL-6) levels measured at baseline have been reported as a circulating biomarker useful for the detection, evaluation of severity and assessment of risk of the progression of interstitial lung disease (ILD) in patients with systemic sclerosis (SSc). In this retrospective study, longitudinal changes in serum KL-6 levels over 2 years were examined in 110 patients with SSc using prospectively collected cohort data. Serum KL-6 levels fluctuated in a significant proportion of the patients but remained stable in the remaining patients. A wide range of variability of longitudinal KL-6 levels was associated with the presence of ILD, diffuse cutaneous SSc, positive anti-topoisomerase I antibodies, negative anticentromere antibodies, increased ILD extent on high-resolution computed tomography, extensive disease, low pulmonary function parameters, high KL-6 levels at baseline and immunomodulatory treatment. Extensive disease was consistently identified as an independent factor associated with variability in KL-6 levels in different models of multiple regression analysis. We failed to demonstrate correlations between trends for KL-6 level changes during the 6 months after SSc diagnosis and ILD progression over 2 years in patients with SSc-ILD. Serum KL-6 levels fluctuate in SSc patients with ILD, especially in those with extensive disease, but the clinical utility of a serial KL-6 level measurement remains uncertain.