Alkaline phosphatase (ALP) is an enzyme found throughout the body, with its highest concentrations in the liver, bones, kidneys, and intestines. This enzyme plays a role in various biological processes, including the breakdown of proteins, the formation and mineralization of bones, and the absorption of nutrients. Measuring ALP levels is a routine part of general health assessments, often included in comprehensive metabolic panels or liver function tests.
Interpreting ALP Levels
The “normal range” for alkaline phosphatase levels can vary slightly among laboratories, but it generally falls between 30 and 147 international units per liter (IU/L) for adults. Children and adolescents typically have higher ALP levels due to active bone growth. Also, pregnant individuals have elevated ALP levels because the placenta produces this enzyme.
An ALP level is considered “high” when it exceeds the upper limit of the established normal range for an individual’s age and sex. A “very high” ALP level indicates a significant elevation, often two to four times or more above the upper limit. Levels surpassing 1000 U/L are notably elevated and may suggest more serious underlying conditions, such as certain cancers or severe liver issues.
Common Causes of High ALP
Significantly elevated ALP levels frequently point to conditions affecting the liver or bones. Liver-related causes often involve blockages in the bile ducts, a condition known as cholestasis, which can result from gallstones, strictures, or tumors. When bile flow is obstructed, ALP accumulates in the liver and leaks into the bloodstream, leading to elevated levels. Other liver conditions contributing to high ALP include hepatitis, cirrhosis, liver tumors, fatty liver disease, and mononucleosis.
Bone disorders are another frequent source of very high ALP. Paget’s disease of bone, characterized by abnormal bone remodeling, can cause ALP levels to rise significantly, sometimes 20 to 30 times the normal reference range. Healing fractures and rapid bone growth also naturally elevate ALP.
Bone tumors, including metastatic or primary bone cancers, can also increase ALP activity. Osteomalacia (due to vitamin D deficiency) and hyperparathyroidism can elevate ALP levels. Other factors include kidney disease, certain cancers like Hodgkin lymphoma, and specific medications such as antibiotics or birth control pills.
When to Seek Medical Advice
A high alkaline phosphatase level is an indicator that warrants further investigation and is not a diagnosis on its own. Consulting a healthcare professional is important for interpreting results within a person’s overall health context. The doctor will evaluate potential causes and determine the appropriate next steps.
Further tests may be ordered to pinpoint the source of the elevated ALP. Tests include an ALP isoenzyme test, differentiating liver or bone origin. Other liver function tests, such as gamma-glutamyl transferase (GGT) and bilirubin, assess liver health.
For suspected bone-related issues, tests measuring calcium, phosphate, parathyroid hormone (PTH), and vitamin D levels may be ordered. Imaging studies, such as ultrasound, CT scans, MRI, or bone scans, can visualize affected organs or bones. The treatment approach for elevated ALP depends on identifying and addressing the underlying medical condition.