Alkaline phosphatase (ALP) is present in a number of tissues including liver, bone, intestine, and placenta. Serum ALP is of interest in the diagnosis of 2 main groups of conditions-hepatobiliary disease and bone disease associated with increased osteoplastic activity. It also is made by the placenta of a pregnant woman. The liver makes more ALP than the other organs or the bones. Some conditions cause large amounts of ALP in the blood. These conditions include rapid bone growth (during puberty), bone disease (such as Paget's disease or cancer that has spread to the bones), a disease that affects how much calcium is in the blood (hyperparathyroidism), vitamin D deficiency, or damaged liver cells.
If the ALP level is high, more tests may be done to find the cause. The amounts of different types of ALP in the blood may be measured and used to determine whether a high level is from the liver or bones. This is called an alkaline phosphatase isoenzymes test.
A test for alkaline phosphatase (ALP) is done to:
- Check for liver disease or damage to the liver. Symptoms of liver disease can include jaundice, belly pain, nausea, and vomiting. An ALP test may also be used to check the liver when medicines that can damage the liver are taken.
- Check bone problems (sometimes found on X-rays), such as rickets, bone tumors, Paget's disease, or too much of the hormone that controls bone growth (parathyroid hormone). The ALP level can be used to check how well treatment for Paget's disease or a vitamin D deficiency is working. An alkaline phosphatase test is often done at the same time as a routine blood test. You do not need to do anything before having a routine blood test.
If you are having a follow-up ALP test, you may be asked to not eat or drink for 10 hours before the test. The ALP level generally goes up after eating, especially after eating fatty foods. Many medicines may change the results of this test. Be sure to tell your doctor about all the nonprescription and prescription medicines you take. Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form.
An alkaline phosphatase (ALP) test measures the amount of the enzyme ALP in the blood.
Very high levels of ALP can be caused by liver problems, such as hepatitis, blockage of the bile ducts (obstructive jaundice), gallstones, cirrhosis, liver cancer, or cancer that has spread (metastasized) to the liver from another part of the body.
High ALP levels can be caused by bone diseases, such as Paget's disease, osteomalacia, rickets, bone tumours, or tumours that have spread from another part of the body to the bone, or by over-active parathyroid glands (hyperthyroidism). Normal healing of a bone fracture can also raise ALP levels.
Heart failure, heart attack, mononucleosis, or kidney cancer can raise ALP levels. A serious infection that has spread through the body (sepsis) can also raise ALP levels. Women in the third trimester of pregnancy have high ALP levels because the placenta makes ALP.
Conditions that lead to malnutrition (such as celiac disease) or are caused by a lack of nutrients in the diet (such as scurvy) can cause low ALP levels. If the ALP level is high, other tests may be done to determine whether a liver or bone problem is present. If liver disease is suspected, more blood tests, an ultrasound, or a CT scan are generally recommended to find the problem. Other tests to check liver function, such as alanine aminotransferase, aspartate aminotransferase, and bilirubin, are often done at the same time as an alkaline phosphatase (ALP) test.
In addition, an increase of 2 to 3 times normal may be observed in women in the third trimester of pregnancy, although the interval is very wide and levels may not exceed the upper limit of the reference interval in some cases. The additional enzyme is of placental origin. Pediatric reference values should be used to properly interpret alkaline phosphatase values in children and adolescents
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