Alkaline phosphatase; alk phos
To screen for or monitor treatment for a liver or bone disorder
As part of liver function tests or when a person has symptoms of a liver or bone disorder
A blood sample drawn from a vein in the arm
Alkaline phosphatase is an enzyme found in high levels in bone and liver. Smaller amounts of ALP are found in pregnant women (in whom ALP is produced by the placenta), and in the intestines. Each of these body parts makes different forms of ALP.
A blood sample is taken by needle from a vein in the arm.
When a person has evidence of liver disease, very high ALP levels can tell the doctor that the person’s bile ducts are somehow partially or totally blocked or inflamed. ALP may also be high if a disease in the bones causes extra ALP to be released from the bones into the bloodstream. ALP is often high in people who have cancer that has spread to the liver and/or the bones. As bone or liver disease improves, ALP levels will decrease.
ALP is generally part of a routine laboratory test profile called liver function tests. It is usually requested with several other tests if a patient has symptoms of a liver or bone disorder.
Raised levels of ALP are usually due to a disorder of either the bone or liver. If other liver function tests such as bilirubin, gamma-glutamyl transferase (GGT), alanine aminotransferase (ALT) or aspartate aminotransferase (AST) are also raised, this usually indicates that the ALP is coming from the liver. However if other liver function tests are normal, this suggests that the ALP might be coming from bone. In some forms of liver disease, such as hepatitis, ALP is usually much less elevated than AST or ALT. However, when the bile ducts are blocked (for example by gallstones, scars from previous gallstones or surgery, or by a tumour), ALP and bilirubin may be increased much more than either AST or ALT. ALP can also be raised in bone diseases such as Paget’s disease (where bones become enlarged and deformed), or in certain cancers that spread to bone.
Pregnancy can increase ALP levels. Children have higher ALP levels because their bones are growing and ALP is often very high during the 'growth spurt' which occurs at different ages in males and females. Occasionally young children may have a very high ALP level for a short time and this is not a sign of disease.
Eating a meal can increase the ALP level slightly for a few hours in some people. Ideally the test should be done after fasting overnight. Some drugs may increase ALP levels, especially some of the drugs used to treat psychiatric problems or epilepsy, but significant increases are rare.
In many cases, liver disease has few symptoms. When the liver is damaged rapidly (a disease called acute hepatitis), the skin and the whites of the eyes often turn yellow. In its late stages, liver disease may cause confusion, easy bruising, swelling in your abdomen and the vomiting of blood.
The doctor may order a special test, such as a test known as `ALP isoenzymes’, to help work out if a high ALP level is caused by liver disease or bone disease. However, usually there would be other signs of either liver or bone disease, such as other abnormal liver enzyme tests.
AST, ALT, GGT, bilirubin, liver function tests, bone markers
Conditions: Liver disease
RCPA Manual: Alkaline phosphatase
Last Review Date: March 9, 2013