Lung alkaline phosphatase as a marker of fibrosis in chronic interstitial disorders

Alkaline phosphatase (ALP) in lung lavage fluids is a marker of tissue damage and type II cell proliferation. Type II pneumocytes are extensively involved in fibrosis. The aim of our study was to verify whether local ALP activity can be held as a marker of fibrosis in chronic interstitial lung disorders. ALP was determined in the bronchoalveolar lavage of 140 subjects: 25 control subjects, and 33 patients with silicosis, 38 with idiopathic pulmonary fibrosis (IPF), and 18 with Stage I, 16 with Stage II, and 10 with Stage III/IV sarcoidosis. We observed a significant augmentation of ALP activity in patients with IPF, as well as in those with Stages II and III/IV sarcoidosis. Albumin was higher in those with Stages I and II sarcoidosis, but it was normal in the other groups. Therefore, a significant increase in ALP:albumin ratio characterized IPF (median, 10.3; range, 2.4 to 83.2) and Stage III/IV sarcoidosis, (8.9, 4.4 to 103.1) as compared with Stage I (2, 1.1 to 18) and Stage II (4.7, 0.7 to 26.6) sarcoidosis, silicosis (6.5, 0.5 to 42.7), and the nonsmoker (6.1, 2.9 to 12.9) and smoker (6.4, 2 to 15.2) control groups. We conclude that an increase of the ALP: albumin ratio in bronchoalveolar lavage fluids from patients with chronic interstitial disorders may reflect a fibrosing progression.