Elevated Serum KL-6 Levels in Patients with Systemic Sclerosis: Association with the Severity of Pulmonary Fibrosis

BACKGROUND: Serum KL-6 has been suggested to be a useful marker for the evaluation of interstitial lung disease activity. OBJECTIVE: To determine the correlation between serum KL-6 levels and pulmonary fibrosis in patients with systemic sclerosis (SSc). METHODS: Serum samples from patients with limited cutaneous SSc (lSSc; n = 19), diffuse cutaneous SSc (dSSc; n = 26) and normal individuals (n = 15) were examined by ELISA. RESULTS: Serum KL-6 levels in SSc patients were significantly higher than those in normal controls. KL-6 levels in dSSc patients were significantly elevated compared with those in lSSc patients. Elevated KL-6 levels were associated with the presence of pulmonary fibrosis in SSc patients or dSSc patients. Furthermore, KL-6 levels inversely correlated with percentages of diffusion capacity of carbon monoxide and vital capacity in SSc patients or dSSc patients. CONCLUSION: KL-6 may be a simple, serologic indicator for the severity of pulmonary fibrosis in SSc.