The biochemical report of pleural fluid is an indicator to determine exudate and leaky fluid. The biochemical examination of pleural fluid includes the following aspects: 1. specific gravity: exudate is higher than 1.020, leaky fluid is lower than 1.020; 2. Levantine test: the routine indicator of pleural fluid is Levantine test, which is a qualitative test of mucin, and the protein test of leaky fluid is negative. 3. cell count: exudate is higher than 200, and the cell count of leaky fluid is lower 4, sugar, chloride also helps to identify exudate and leaky fluid.