Alkaline phosphatase is an enzyme found mainly in the liver and bones, and its levels can be measured with a blood test. Abnormal alkaline phosphatase levels may be linked to liver, bile duct, bone, thyroid, or nutritional problems.
High alkaline phosphatase may occur with conditions such as hepatitis, bile duct obstruction, hyperparathyroidism, or increased bone formation. Low alkaline phosphatase is less common and may be associated with malnutrition, hypothyroidism, or deficiencies in minerals such as zinc and magnesium.
Alkaline phosphatase levels can also vary with age, sex, pregnancy, and laboratory reference ranges. Test results are often evaluated along with symptoms and other liver-related tests to help identify the underlying cause.
What results mean
The amount of alkaline phosphatase in the blood can help identify certain conditions that should be evaluated by a healthcare provider.
1. Alkaline phosphatase high
Alkaline phosphatase levels may be high in the following situations:
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Pancreatic diseases, such as chronic pancreatitis or cancer
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Bile duct diseases, such as bile flow obstruction or bile duct cancer
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Liver diseases, such as hepatitis, cirrhosis, or tumors
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Cancer
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Leukemia
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Infections
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Kidney failure
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Heart attack
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Benign familial hyperphosphatemia
Alkaline phosphatase levels may also be high when bone formation increases, such as with some bone cancers, osteomalacia, or hyperparathyroidism.
According to the National Institute of Arthritis and Musculoskeletal and Skin Diseases, high alkaline phosphatase levels may also be a sign of Paget's disease of bone.
Levels can also rise normally during growth, in adults over 60 due to bone changes, and during pregnancy, especially in the third trimester, when the placenta produces more alkaline phosphatase.
2. Alkaline phosphatase low
Low alkaline phosphatase levels are uncommon. However, levels may be decreased in the following situations:
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Hypophosphatasia, a genetic disorder that can cause bone abnormalities and fractures
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Malnutrition
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Severe diarrhea
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Celiac disease
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Enteritis
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Magnesium, zinc, vitamin B6, folic acid, or vitamin C deficiency
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Protein deficiency
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Heart surgery
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Congenital hypothyroidism, which can cause problems with growth and development
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Pernicious anemia and aplastic anemia
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Chronic myeloid leukemia, also known as chronic granulocytic leukemia
Some medications, including birth control pills and hormone replacement therapy used during menopause, may also cause a slight decrease in alkaline phosphatase levels.
Indications for testing
An alkaline phosphatase test may be ordered if you have signs or symptoms of liver or bile duct problems, such as abdominal swelling, right-sided abdominal pain, jaundice, dark urine, pale stools, or widespread itching.
The test may also be recommended if you have signs or symptoms affecting the bones, such as widespread bone pain, bone deformities, or fractures.
How the test is performed
An alkaline phosphatase test is performed using a blood sample taken from a vein in the arm. The sample is then sent to a laboratory for analysis.
Reference ranges
According to a study published in Laboratory Medicine, alkaline phosphatase reference ranges vary by age and sex. In adults over 18, the reported ranges were 55-140 U/L for males and 60-147 U/L for females.
Children and adolescents generally have higher levels because of bone growth. Because ranges can vary by laboratory and testing method, results should be interpreted using the range provided with the test.
During pregnancy, alkaline phosphatase levels may also be higher because the placenta produces this enzyme.
A healthcare provider may also order other liver-related tests, such as AST and ALT, GGT, and bilirubin, as well as imaging tests or, in some cases, a liver biopsy.
