The alkaline phosphatase test (ALP) is used to help detect liver disease or bone disorders.
In conditions affecting the liver, damaged liver cells release increased amounts of ALP into the blood. This test is often used to detect blocked bile ducts because ALP is especially high in the edges of cells that join to form bile ducts. If one or more of them are obstructed, for example by a tumor, then blood levels of ALP will often be high.
Any condition that affects bone growth or causes increased activity of bone cells can affect ALP levels in the blood. An ALP test may be used, for example, to detect cancers that have spread to the bones or to help diagnose Paget's disease, a condition that causes malformed bones. This test may also sometimes be used to monitor treatment of Paget's disease or other bone conditions, such as vitamin D deficiency.
If ALP results are increased but it is not clear whether this is due to liver or bone disease, tests for ALP isoenzyme may be done to determine the cause. A GGT test and/or a test for 5'-nucleotidase may also be done to differentiate between liver and bone disease. GGT and 5'-nucleotidase levels are increased in liver disease but not in bone disorders.
An ALP test may be ordered as part of routine laboratory testing, often with a group of other tests called a liver panel. It is also usually ordered along with several other tests when a person has symptoms of a liver or bone disorder.
If it is not clear from signs and symptoms or from other routine tests whether the high ALP is from liver or bone, then a test for ALP isoenzymes may be necessary to distinguish between bone and liver ALP.
ALP in liver disease ALP results are usually evaluated along with other tests for liver disease. In some forms of liver disease, such as hepatitis, ALP 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 AST or ALT. ALP may also be increased in liver cancer.
ALP in bone disease In some bone diseases, such as Paget's disease, where bones become enlarged and deformed, or in certain cancers that spread to bone, ALP may be increased.
If a person is being successfully treated for Paget's disease, then ALP levels will decrease or return to normal over time. If someone with bone or liver cancer responds to treatment, ALP levels should decrease.
Low levels of ALP may be seen temporarily after blood transfusions or heart bypass surgery. A deficiency in zinc may cause decreased levels. A rare genetic disorder of bone metabolism called hypophosphatasia can cause severe, protracted low levels of ALP. Malnutrition or protein deficiency as well as Wilson disease could also be possible causes for lowered ALP.
Pregnancy can increase ALP levels. Temporary elevations are also seen with healing fractures.
Children and adolescents normally have higher ALP levels than adults because their bones are growing, and ALP is often very high during a growth spurt, which occurs at different ages in boys and girls.
Some drugs may affect ALP levels. For example, oral contraceptives may decrease levels while anti-epileptics may increase levels.
This article was last reviewed on October 29, 2013. | This article was last modified on June 4, 2014.
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