Alkaline phosphatase

Alkaline phosphatase is an enzyme which hydrolyses phosphate esters at alkaline pH. There are different forms (isoenzymes) produced in the body. Clinically the most important of these are liver and bone, but also in some cases placental and intestinal.

The clinical picture, whether other LFTs eg GGT are elevated, usually help guide whether an elevated alkaline phosphatase is coming from the liver or not. If in doubt, alkaline phosphatase isoenzymes can be measured.

Liver

Hepatobiliary disease, for example from obstruction, results in the induction of alkaline phosphatase synthesis in the liver with leakage of the enzyme into plasma.

Drugs also will result in enzyme induction.

Bone

Alkaline phosphatase is produced from osteoblasts. Hence bone disease can result in an elevated alkaline phosphatase - malignancy, osteomalacia, Pagets disease.

Intestine

After a fatty meal intestinal alkaline phosphatase may be released into the plasma so it is worthwhile in unclear cases to check the alkaline phosphatase after the patient has fasted overnight.

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