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To screen for or monitor treatment for a liver or bone disorder
As part of a routine liver panel or when you have symptoms of a liver or bone disorder
A blood sample drawn from a vein in your arm
Fasting overnight preferred but not required
Alkaline phosphatase (ALP) is an enzyme found in several tissues throughout the body. The highest concentrations of ALP are present in the cells that comprise bone and the liver. Elevated levels of ALP in the blood are most commonly caused by liver disease or bone disorders. This test measures the level of ALP in the blood.
In the liver, ALP is found on the edges of cells that join to form bile ducts, tiny tubes that drain bile from the liver to the bowels, where it is needed to help digest fat in the diet. ALP in bone is produced by special cells called osteoblasts that are involved in the formation of bone. Each of the various tissue types produces distinct forms of ALP called isoenzymes.
ALP blood levels can be greatly increased, for example, in cases where one or more bile ducts are blocked. This can occur as a result of inflammation of the gallbladder (cholecystitis) or gallstones. Smaller increases of blood ALP are seen in liver cancer and cirrhosis, with use of drugs toxic to the liver, and in hepatitis.
Any condition causing excessive bone formation, including bone disorders such as Paget's disease, can cause increased ALP levels. Children and adolescents typically have higher blood ALP levels because their bones are still growing. As a result, the ALP test must be interpreted with different reference (normal) values for children and for adults.
It is possible to distinguish between the different forms (isoenzymes) of ALP produced by different types of tissues in the body. If it is not apparent from clinical signs and symptoms whether the source of a high ALP test result is from liver or bone disease, then a test may be performed to determine which isoenzyme is increased in the blood.
A blood sample is drawn by needle from a vein in the arm.
Fasting is preferred but not required for this test. Eating a meal can increase the ALP level slightly for a few hours in some people. It is usually better to do the test after fasting overnight. In this case, only water is permitted.
The alkaline phosphatase test (ALP) is used to help detect liver disease or bone disorders.
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.
Signs and symptoms of liver involvement may include:
Some examples of the signs and symptoms suggesting a bone disorder include:
High ALP usually means that either the liver has been damaged or a condition causing increased bone cell activity is present.
If other liver tests such as bilirubin, aspartate aminotransferase (AST), or alanine aminotransferase (ALT) are also high, usually the increased ALP is coming from the liver. If GGT or 5'-nucleotidase is also increased, then the high ALP is likely due to liver disease. If either of these two tests is normal, then the high ALP is likely due to a bone condition. Likewise, if calcium and/or phosphorus measurements are abnormal, usually the ALP is coming from bone.
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.
Moderately elevated ALP may result from other conditions, such as Hodgkin's lymphoma, congestive heart failure, ulcerative colitis, and certain bacterial infections.
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.
There are other commonly used liver tests that measure other enzymes found in liver cells, such as alanine aminotransferase (ALT) and aspartate aminotransferase (AST). A test for bilirubin, a substance produced by the breakdown of red blood cells and removed from the body by the liver, may also be performed. Sometimes these tests (along with albumin and total protein testing) are run together as a liver panel. Other tests that may be performed individually or as part of a liver panel to detect or monitor liver disease include gamma-glutamyl transferase (GGT), lactate dehydrogenase (LDH), and prothrombin time (PT).
Some of those who are at risk of liver disease include the following:
See the article on Liver Disease for more on these.
Depending on the cause, your condition may be diagnosed and/or monitored using other tests such as calcium, phosphorus, parathyroid hormone, vitamin D, or bone markers (a group of tests used to measure bone formation and bone resorption).
LOINC Observation Identifiers Names and Codes (LOINC®) is the international standard for identifying health measurements, observations, and documents. It provides a common language to unambiguously identify things you can measure or observe that enables the exchange and aggregation of clinical results for care delivery, outcomes management, and research. Learn More.
Listed in the table below are the LOINC with links to the LOINC detail pages.
|LOINC||LOINC Display Name|
|1783-0||ALP (Bld) [Catalytic activity/Vol]|
|77141-0||ALP (S/P/Bld) [Catalytic activity/Vol]|
|6768-6||ALP [Catalytic activity/Vol]|
Sources Used in Current Review
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