Alkaline phosphatase is a kind of phosphomonoesterase, which widely exists in human tissues and body fluids, including bone, liver, breast, intestinal mucosa, kidney and placenta. This enzyme can catalyze the removal of 5 'phosphate groups from nucleic acid molecules, thereby converting the 5' - P end of DNA or RNA fragments into the 5 '- OH end. But it is not a single enzyme, but a group of isoenzymes. Six isoenzymes, AKP1, AKP2, AKP3, AKP4, AKP5, and AKP6, have been identified. Among them, the first, second and sixth are from the liver, the third is from bone cells, the fourth is from placenta and cancer cells, and the fifth is from intestinal villous epithelium and fibroblasts. The ALP in serum mainly comes from the liver and bones. Most of the serum in growing children comes from osteoblasts and growing osteochondrocytes, with a small amount coming from the liver. The determination of Alkaline phosphatase is mainly used to diagnose hepatobiliary and Skeleton diseases, and is an important indicator to reflect extrahepatic biliary obstruction, intrahepatic space occupying lesions and Rickets.