written by: Dr Mike C
• edited by: Leigh A. Zaykoski
• updated: 1/31/2010
Alkaline phosphatase is an enzyme that is involved in the production of bone, so it is found at higher levels in children than in adults. The enzyme is primarily produced in mucosal cells that line the bile duct. Low alkaline phosphatase levels are linked to a wide range of conditions.
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Alkaline Phosphatase Explained
Alkaline phosphatase is an enzyme that is associated with the calcification process in developing bones. The role was first suggested as long ago as 1923 by Robison. It is involved in development of the bone matrix itself and in skeletal growth. The enzyme is responsible for removing pyrophosphates which would otherwise inhibit the ossification (bone forming) process.
The alkaline phosphatases are a group of enzymes mainly associated with the liver and bone, but are also found in cells in the intestines, placenta and kidneys. Since this enzyme is associated with bone growth, it is naturally higher in children (whose bones are continuing to develop) than adults. Alkaline phosphate levels will also rise when the body is in the process of mending a broken bone. The enzyme is associated with osteoblasts, the cells that lay down new bone. Osteoblasts require an alkaline environment to lay down bone and alkaline phosphatase is involved in this process.
The enzyme is produced by the mucosal cells that line the bile system of the liver. If there is disease in the liver, bile ducts or gallbladder, alkaline phosphatase is released to the blood stream causing its level to rise. Alkaline phosphatase levels are measured when there are concerns over liver or bone diseases, primarily. However, low alkaline phosphate can be associated with a range of other conditions; this is also the case with abnormally high levels.
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Normal Levels Of Alkaline Phosphatase In Healthy Adults
In laboratory testing, the total amount of alkaline phosphatase is determined in the patient’s blood sample, although the enzyme itself is inactive in blood. The enzyme needs to be in an alkaline environment to function (with a pH of 10) and that is why it is inactive at the normal physiological pH of blood which is 7.4. In the normal adult population, the range of alkaline phosphatase is between 50 to 75 mg/dl. The assay must be performed only when the patient has fasted since ingestion of food will cause the level of the enzyme to rise in the bloodstream which can lead to erroneous clinical data.
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Associated Conditions and Diseases
Reduced alkaline phosphatase levels are associated with a number of conditions including zinc deficiency; folic acid deficiency; low levels of phosphorus; vitamin B6 deficiency; vitamin C deficiency; excessively high vitamin D intake; malnutrition involving inadequate protein assimilation (this can also be caused by hypochlorhydria – low production of stomach acid); Celiac disease; hypothyroidism; anaemia or inadequate parathyroid gland function.
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Treatment of Reduced Levels
The treatment of low alkaline phosphatase levels will involve investigating the underlying cause and treating it. If the condition is because of a deficiency, it would normally be treated with supplements of the causative agent.
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In Journal of Nurition: http://jn.nutrition.org/cgi/reprint/109/8/1477.pdf
Robison R (1923) The possible significance of hexose phosphoric esters in ossification. Biochem J. 17; 286-293.