ADA is mostly used in hepatobiliary diseases and tuberculosis 1, ADA is only mildly to moderately increased in acute hepatitis; in chronic active hepatitis and hepatic sclerosis, the positive rate of ADA activity can reach about 90% and the degree of increase is more obvious; in severe hepatitis, ALT is not high, but ADA is often significantly increased; in obstructive jaundice, ADA activity is rarely increased. 2, Determination of ADA activity in thoracoabdominal fluid and cerebrospinal fluid specimens has differential diagnostic value. The ADA activity in tuberculous thoracoabdominal fluid is significantly higher than that in cancer and inflammatory thoracoabdominal fluid, which has high sensitivity and specificity for early diagnosis of tuberculous thoracic and peritonitis. 3, cerebrospinal fluid ADA test can be used as an important indicator for the diagnosis and differential diagnosis of central nervous system diseases, and ADA activity is elevated in tuberculous meningitis, but not in viral meningitis.