Alkaline phosphatase -- commonly abbreviated as ALP -- is a protein found in all cells of the body. The highest concentrations of ALP are located in cells of the liver, bones and bile ducts. ALP in the blood is primarily derived from excess ALP that is released from these cells. Blood levels of ALP are often measured as part of routine blood tests. Although many conditions, including liver and bone diseases, can cause high levels of ALP, low blood ALP levels are uncommon. Malnutrition is the main cause of low ALP levels, but some genetic diseases, other medical conditions and medications can lead to low ALP levels as well.
Low ALP levels may occur in individuals with malnutrition, especially when their protein or overall calorie intake is low. Children may be more likely than adults to develop low blood ALP levels from poor nutrition because their growing bodies have higher requirements for protein, calories and other nutrients. Malnutrition may be caused by a poor diet or by any condition that interferes with the absorption of food, such as celiac disease. When malnutrition is the cause of low ALP levels, other signs of poor nutrition will likely be evident as well. These signs include a low body weight and low blood levels of other proteins, vitamins and minerals, such as magnesium and zinc.
Less commonly, a low ALP is the result of a genetic disease. Hypophosphatasia is a rare genetic disorder that causes decreased ALP levels. This disorder is due to a mutation in the gene that produces ALP. Because ALP is important for the growth of strong teeth and bones, individuals with hypophosphatasia have poor teeth and are susceptible to bone fractures. When hypophosphatasia is severe, it is evident in early childhood. However, milder forms of hypophosphatasia may not be diagnosed until an individual is in his or her 20's or 30's. Wilson's disease is another rare genetic disease that may cause low ALP levels. This disease results from a mutation that causes large amounts of copper to accumulate in the body. Low levels of ALP in Wilson's disease primarily occur in individuals who have severe liver failure.
Low ALP levels may occur temporarily after heart surgery or after a blood transfusion. An "underactive thyroid" -- known as hypothyroidism -- may also sometimes cause low ALP levels. Severe anemia, particularly if it is due to vitamin B12 deficiency, may rarely lead to a low ALP. Some medications, such as birth control pills in younger women and estrogen replacement therapy in older women, may also cause low ALP levels.
Treatment for Low ALP
No treatment may be necessary if ALP levels are only slightly or temporarily low. Any treatment that may be required will depend on the underlying cause of the low ALP. This may involve improving nutrition and/or avoiding medications or treating medical conditions that cause low ALP levels.
- Medline Plus: ALP - Blood Test
- National Institute of Diabetes and Digestive and Kidney Diseases: Wilsons Disease
- Archives of Physiology and Biochemistry: Relation of Oxidative Stress, Zinc an Alkaline Phosphatase in Protein Energy Malnutrition; Jain, A., et al.; Feb. 2013
- Genetics Home Reference: Hypophosphatasia
- Hypophosphatasia; Mornet, Etienne, and Nunes, Mark E; 2007