Seasonal variation of serum KL-6 concentrations is greater in patients with hypersensitivity pneumonitis

BACKGROUND: Serum KL-6 is a useful biomarker for the diagnosis of interstitial lung diseases (ILD). However, KL-6 has not been used to discriminate different types of ILD. Serum KL-6 concentrations can vary depending on antigen exposure levels in patients with hypersensitivity pneumonitis (HP); however, seasonal changes in serum KL-6 concentrations in ILD have not been determined. We hypothesized that seasonal variation of serum KL-6 is greater in HP than for the other ILD. The aim of this study was to determine seasonal variation of serum KL-6 concentrations in various ILD. METHODS: Serum KL-6 concentrations in the summer season from June 1 to September 30 and the winter season from November 1 to February 28 were retrospectively analyzed in patients with idiopathic pulmonary fibrosis (IPF, n = 16), non-specific interstitial pneumonia (NSIP, n = 16), collagen vascular disease-associated interstitial pneumonia (CVD-IP, n = 33), house-related HP (House-HP, n = 9), bird-related HP (Bird-HP, n = 9), and combined pulmonary fibrosis and emphysema (CPFE, n = 13). RESULTS: Bird-HP and House-HP showed greater seasonal serum KL-6 variation than the other ILD. Serum KL-6 concentrations in Bird-HP were significantly increased in the winter and KL-6 concentrations in House-HP were significantly increased in the summer. Serum KL-6 variation was significantly greater in acute HP than chronic HP. Receiver operating characteristic curve analysis revealed that greater seasonal variation in serum KL-6 concentrations is diagnostic for Bird-HP. CONCLUSION: HP should be considered in ILD with greater seasonal changes in serum KL-6 concentrations.