Prognostic value of circulating KL‐6 in idiopathic pulmonary fibrosis

Objective: Circulating levels of KL‐6, a high MW glycoprotein (MUC1 mucin), are elevated in a majority of patients with a number of interstitial lung diseases, including idiopathic pulmonary fibrosis (IPF). However, KL‐6 levels vary from patient to patient. The aim of the present study was to determine whether the serum KL‐6 level at the time of diagnosis predicts prognosis in IPF. Methods: The relationship between clinical variables and prognosis in 27 patients with IPF were analysed retrospectively. The diagnosis was made by histological examination ( n = 16) or on clinical findings including high‐resolution CT scanning ( n = 11). All patients were followed up for at least 3 years. Variables such as age, FVC%, PaO 2 at rest, initial LDH level, C‐reactive protein and KL‐6 were used for analysis. Results: At the cut‐off level determined by receiver operating characteristic curves, LDH and KL‐6 showed a significant correlation with the patient's prognosis by univariate analysis. However, multivariate analysis revealed that only KL‐6 was a predictor of prognosis. The patients were categorized by their serum KL‐6 levels (as above or below the cut‐off level of 1000 U/mL) and their survival estimated using the Kaplan–Meier method. The difference in median survival between the two groups was significant. The median survival of patients with low KL‐6 was more than 36 months, whereas that of patients with high KL‐6 was only 18 months. Conclusion: These results suggest that initial evaluation of serum KL‐6 level can predict survival in patients with IPF.