[Concentration of alkaline phosphatase (AP) and AP/albumin ratio in bronchoalveolar lavage (BAL) for the diagnosis of interstitial lung diseases].

As a result of several studies with different animal models there is evidence that the concentration of AP in BAL is produced in the pneumocyte II and that an increase of AP in the BAL is a marker of tissue damage. By measuring AP in the BAL of patients with interstitial lung diseases we investigated its potential role as a diagnostic tool. To detect plasma leakage we also measured the concentration of albumin in the BAL. We studied 85 patients with following diagnoses: Sarcoidosis in 34 patients (Stage 1/2/3 14/7/13), idiopathic pulmonary fibrosis (IPF) in 14, bronchiolitis obliterans with organizing pneumonia (BOOP) in 7, hypersensitivity pneumonitis (HP) in 6. The control group consisted in 24 patients (13 nonsmokers, 11 smokers). In IPF and BOOP we observed significantly higher concentrations of AP than in controls and sarcoidosis (42.4 +/- 36.6 and 35.6 +/- 16 vs. 15.8 +/- 12.7 and 15.0 +/- 9.8 U/l, p < 0.05, ANOVA). Compared with controls in sarcoidosis higher concentrations of albumin (5.7 +/- 4 vs. 13.2 +/- 10 mg/dl, p < 0.05, ANOVA) and a lower AP/albumin-ratio (3.6 +/- 3.0 vs. 1.3 +/- 0.9 U/10 mg, p < 0.05, ANOVA) were seen. This result is an argument against plasma leakage as the source of AP in BAL. There were no differences in AP and albumin between the different stages of sarcoidosis and between smokers and nonsmokers in the control group. We conclude, that there are different concentrations of AP and albumin in BAL in different interstitial lung diseases. Compared with controls we observed higher concentrations of AP and an AP/albumin-ratio in the normal range in IPF, a normal concentration of AP and a lowered AP/albumin-ratio in sarcoidosis.