Increase of KL-6 in sera of uveitis patients with sarcoidosis

Background KL-6 is a human glycoprotein secreted by type II alveolar cells in lung, and its serum levels increase in pneumonia of various causes. KL-6 is a member of the MUC-1 family, which is expressed in lung, cornea, and conjunctiva. The purpose of the present study was to investigate the clinical usefulness of quantifying serum KL-6 levels for diagnosing sarcoidosis in patients with uveitis. Methods Sera were obtained from 24 uveitis patients diagnosed with sarcoidosis, 37 uveitis patients with other etiologies, and 138 healthy control subjects. Serum concentration of KL-6 was determined by a human KL-6 electrochemiluminescence immunoassay. Results The average level of KL-6 in the sera of uveitis patients with sarcoidosis was 387 U/ml. This was significantly higher than in healthy subjects and uveitis patients with other etiologies. The KL-6 measurements identified 45.8% of sarcoidosis-positive patients. When the KL-6 results were combined with serum angiotensin-converting enzyme (ACE) concentrations, 87.5% of sarcoidosis patients were identified, compared to 66.7% using ACE results alone. The combined measurement identified 10.8% of the non-sarcoid patients and 0.72% of healthy subjects as positive (false positive). Conclusion Combined measurements of serum KL-6 and ACE may be useful as a screening for sarcoidosis in uveitis patients.