KL-6 as a novel serum marker for interstitial pneumonia associated with collagen diseases.

To investigate the diagnostic value of the serum concentrations of KL-6, a mucinous glycoprotein expressed on type II pneumocytes, for interstitial pneumonia (IP) in various collagen diseases.Serum KL-6 levels were measured by ELISA.The mean values and the positive rates of serum KL-6 levels for patients with rheumatoid arthritis, systemic sclerosis, or polymyositis/dermatomyositis with IP were significantly higher than those without IP. Sensitivity, specificity, positive and negative predictive values of serum KL-6 level for IP associated with collagen diseases were 60.7, 98.9, 97.4, and 77.1%, respectively. The mean serum KL-6 level of patients with active IP was significantly (p = 0.0001) higher than that of patients with inactive IP. Serum KL-6 levels increased with the deterioration of IP, while the successful treatment of IP resulted in a significant decrease of these levels.Serum KL-6 concentration levels are a useful marker for diagnosis and evaluation of the disease activity of IP associated with collagen diseases.