Alkaline Phosphatase

Alkaline phosphatase (ALP) (EC 3.1.3.1) is a hydrolase enzyme responsible for removing phosphate groups from many types of molecules, including nucleotides , proteins, and alkaloids. The process of removing the phosphate group is called dephosphorylation. As the name suggests, alkaline phosphatase's are most effective in an alkaline environment.

The follwing is from labtest online: When a person has evidence of liver disease , very high ALP levels can tell the doctor that the person’s bile ducts are somehow blocked. Often, ALP is high in persons who have cancer that has spread to the liver or the bones, and doctors can do further testing to see if this has happened. If a person with bone or liver cancer responds to treatment, ALP levels will decrease. When a person has high levels of alkaline phosphatase, and the doctor is not sure why, s/he may also order alkaline phosphatase isoenzyme tests to try to determine the cause.

Accoring to Labone, Alkaline Phosphatase is generally part of a routine lab testing profile, often with a group of other tests called a liver panel. Alkaline phosphatase is also usually ordered along with several other tests if a patient seems to have symptoms of a liver or bone disorder.

High Alkaline Phosphatase usually means that the bone or liver has been damaged. If other liver tests such as bilirubin , aspartate aminotransferase (AST), or alanine aminotransferase (ALT) are also high, usually the ALP is coming from the liver. If calcium and phosphate measurements are abnormal, usually the ALP is coming from bone.

In some forms of liver disease, such as hepatitis, alkaline Phosphatase is usually much less elevated than AST and ALT. When the bile ducts are blocked (usually by gallstones, scars from previous gallstones or surgery, or by cancers), ALP and bilirubin may be increased much more than Aspartate aminotransferaseAST or Alanine transaminaseALT. In a few liver diseases, ALP may be the only test that is high.

In some bone diseases, such as a disorder called Paget’s disease(where bones become enlarged and deformed), or in certain cancers that spread to bone, ALP may be the only test result that is high.

Sometimes doctors don’t know why alkaline phosphatase is high, and they need to order other tests to determine the exact cause. In such cases, your doctor may order another enzyme, gamma glutamyl transpeptidase gGT, that is made by the liver in the same places as is ALP, but which is not made by bone.