Alkaline phosphatase ( alkaline phosphatase , ALP ) is an enzyme produced mainly by the liver epithelia and osteoblasts ( cells forming new bone ) ; This enzyme also comes from the gut , renal proximal tubules , placenta and mammary glands were making milk . Alkaline phosphatase secreted through bile duct . Increases in serum when there are obstacles in the bile ducts ( cholestasis ) . ALP test is primarily used to determine whether there is liver disease ( hepatobiliary ) or bone .