New Serum Indicator of Interstitial Pneumonitis Activity: Sialylated Carbohydrate Antigen KL-6

Serum levels of a high molecular weight circulating antigen KL-6, detected by means of a sandwich assay using a monoclonal antibody KL-6 against a sialylated carbohydrate antigen, were evaluated for usefulness in monitoring the activity of interstitial pneumonitis. Abnormally high levels of KL-6 antigen were observed in the sera of 34 (58 percent) of 59 patients with interstitial pneumonitis. There was no significant correlation between serum values of KL-6 antigen and LDH activity. There was a positive correlation between KL-6 antigen levels and the degree of clinical disease activity as measured by 67 Ga-citrate scintigram and the clinical course. Though this is a preliminary study, these observations suggest that the serum level of KL-6 antigen may be a useful indicator of disease activity in patients with interstitial pneumonitis. It does not appear to be useful, however, in the differential diagnosis of interstitial pneumonitis from malignant and nonmalignant diseases. (Chest 1989; 96:68-73)