Alkaline phosphatase -- commonly abbreviated as ALP -- is a protein found in all cells of your body. Cells in the bile ducts, liver and bones have especially high amounts of ALP. The ALP in your blood primarily comes from excess ALP 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 ALP levels are uncommon. Poor nutrition is one of the main causes of low ALP, but some genetic diseases, other medical conditions and medications can also produce low ALP levels.
Low ALP may occur in people with poor nutrition, 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 nutritional requirements. Poor nutrition may be caused by a poor diet or any condition that interferes with the absorption of food nutrients, such as celiac disease.
When poor nutrition is the cause of low ALP levels, other signs of inadequate nutrient intake may be evident as well. These signs include a low body weight and low blood levels of other proteins, vitamins and minerals.
Less commonly, low ALP is the result of a genetic disease. Hypophosphatasia is a rare genetic disorder that produces low ALP levels. It is caused by a mutation in the gene that produces ALP, according to Genetics Home Reference. Because ALP is important for the growth of strong teeth and bones, individuals with hypophosphatasia have poor teeth and are susceptible to fractures. When hypophosphatasia is severe, it is evident at birth or in early childhood. Milder forms of hypophosphatasia may not be diagnosed until a person is in his or her 20s or 30s.
Wilson disease is another rare genetic disorder that may produce low ALP levels. This condition is due to a mutation that causes large amounts of copper to accumulate in the body. Low levels of ALP in Wilson disease primarily occur in people with extensive accumulation of copper in the liver.
Low ALP levels may occur temporarily after heart surgery or a blood transfusion. An underactive thyroid -- 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. Zinc and magnesium deficiencies can also produce a low ALP, according to a study reported in "Current Research in Nutrition and Food Science" in December 2017. Some medications, such as birth control pills in younger women and estrogen replacement therapy in older women, may cause low ALP levels as well.
When your ALP is low, your doctor will likely want to determine the cause. Other results in your routine blood tests may provide helpful clues. Additional blood tests or other investigations may be required.
Low ALP levels are treated by dealing with the underlying cause. This may involve improving your nutrition, avoiding certain medications or treating medical conditions that cause low ALP.
Reviewed by Mary D. Daley, M.D.
- Medline Plus: ALP -- Blood Test
- National Institute of Diabetes and Digestive and Kidney Diseases: Wilson Disease
- Genetics Home Reference: Hypophosphatasia
- Hypophosphatasia; Mornet E and Nunes ME
- Current Research in Nutrition and Food Science: Alkaline Phosphatase (ALP) In Adult Population an Indicator of Zinc (Zn) and Magnesium (Mg) Deficiency
- Archives of Physiology and Biochemistry: Relation of Oxidative Stress, Zinc and Alkaline Phosphatase in Protein Energy Malnutrition
- Merck Manual Professional Version: Overview of Undernutrition