Serum alkaline phosphatase means that alkaline phosphatase is a phosphate monoester hydrolase that hydrolyzes phosphate monoester to produce phosphate in an alkaline environment. Alkaline phosphatase is mainly distributed on the blood sinusoidal side of hepatocytes and on the microvilli on the capillary side of the bile duct, and is excreted into the small intestine via bile. In addition, alkaline phosphatase from bone, intestine, kidney, placenta, etc. is also excreted with bile, so alkaline phosphatase is significantly increased when bile is stagnant. Alkaline phosphatase can also be elevated when there is a problem with the bones, and can be produced in excess by osteoblasts that are hyperactive and active in bone disease or by cancer cells in cancer patients.