Alkaline Phosphatase Test

Other names: ALP Test; Alk. Phos.

The ALP test measures the levels of alkaline phosphatase in the blood; alkaline phosphatase is an enzyme, which is found in many cells in the body. It is most concentrated in the bone and liver cells. There are various forms of the enzyme, known as isoenzymes; these are categorised by where they are produced in the body. The ALP in the bone cells is produced by osteoblasts, cells which are responsible for the formation of bone, while ALP in the liver cells is found on the edge of the cells which lead to the bile ducts.

What is the test used for?

The ALP test is used to test for disorders of the liver and bone. The test may be ordered as part of a set of routine liver tests.

How is the test performed?

The test is done using a sample of blood from a vein in the arm; the needle is inserted into a vein in the arm and the blood sample is collected in a syringe. Once the doctor has obtained enough blood, the sample will be bottled, labelled and sent away to a laboratory for analysis. Sometimes, patients will be asked to fast for a period of time before the test; however, this is not always necessary.

What do the test results mean?

High levels of ALP may indicate liver and bone conditions:

  • Liver conditions: high levels of ALP may indicate liver cancer, gall stones (which block the bile ducts and prevent bile from being drained) or hepatitis. Usually, doctors will carry out different types of liver tests to reach a diagnosis and high or low levels of other enzymes or chemicals may help them to reach an accurate diagnosis.
  • Bone conditions: high levels of ALP may indicate Paget’s disease, which causes the bones to become enlarged. Sometimes, higher levels of ALP may also occur after a blood transfusion or heart bypass surgery.

Levels of ALP may increase during pregnancy and taking certain medications may affect the level of ALP in the blood; oral contraceptives may decrease the level of ALP in the blood, while anti-epileptic drugs may cause the levels to decrease.

Specific Blood Tests

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