Alkaline Phosphatase (AP) is an enzyme, which is primarily present in the liver and bones. However, small traces of enzyme are also present in intenstines and kidneys of a person and the placenta of a pregnant woman.

In normal conditions, the liver manufacrures more AP than bones and kidneys. But sometimes, a large amount of AP is discharged into the bloodstream. One of such conditions involves rapid bone development during puberty. A person may also have a higher rate of AP, if suffering from bone diseases, such as Paget's disease or Osteomalacia. Other than this, a person with damaged liver cells may also experience higher rate of AP.

The AP test measures the total amount of alkaline phosphatases released into the blood from different tissues. The AP performs well at an alkaline pH of 10. However, the enzyme is sedentary in blood. The chemical formula of AP produced by the liver is somewhat different from the formula of AP produced by the bones. Therefore, the person experiencing high levels of AP in blood is required to go for further tests to identify the exact cause.

The AP test is required to diagnose various liver diseases, such as jaundice, nausea, and abdominal pain. Other than this, this test also helps in identifying the cause and course of different bone diseases, such as rickets, bone tumors, osteomalacia, or Paget's disease. The AP test also helps in tracking the effect of medicine for such bone diseases.