Understanding Alkaline Phosphatase
Alkaline phosphatase (ALP) is an enzyme found throughout the human body, particularly concentrated in the liver and bones. As an enzyme, ALP facilitates various biological processes. Measuring ALP levels through a simple blood test can provide insights into a person’s health, as abnormal levels can indicate underlying issues.
ALP primarily functions in bone formation and liver processes. In bones, osteoblasts produce ALP, which is involved in the mineralization process that gives bones strength. Within the liver, ALP is associated with bile ducts and aids in protein breakdown. It is also present in the kidneys, intestines, and, during pregnancy, in the placenta.
Different forms of ALP, called isoenzymes, originate from these tissues. A standard blood test measures total ALP activity. The “normal range” for ALP, typically 20 to 140 International Units per liter (IU/L), can vary between laboratories and also based on age and gender. For example, growing children often have higher ALP levels due to active bone growth.
Interpreting Elevated Levels
Elevated alkaline phosphatase levels most frequently point to conditions affecting the liver or bones. When the liver is involved, increased ALP often suggests an issue with the bile ducts, which transport bile from the liver to the small intestine. Conditions like cholestasis (obstructed bile flow) or hepatitis (liver inflammation) can cause ALP levels to rise. Cirrhosis, severe liver scarring, and liver tumors can also increase ALP as liver function is compromised.
Bone conditions are another major contributor to high ALP levels, especially those involving increased bone turnover. Paget’s disease of bone, a disorder of excessive bone breakdown and regrowth, can result in very high ALP readings. Other conditions like osteomalacia in adults or rickets in children, both involving bone softening due to inadequate mineralization, also cause elevations. Bone fractures, active bone healing, and primary bone tumors or metastatic cancer that has spread to the bones can similarly increase ALP.
Other factors can influence ALP levels. Hyperparathyroidism, where parathyroid glands produce too much parathyroid hormone, can indirectly affect bone turnover and raise ALP. Certain cancers, including those of the kidney or lung, may also be associated with elevated ALP. Additionally, some severe infections and specific medications can transiently increase ALP activity in the blood.
Physiological variations can also cause temporary ALP elevations that are not medically concerning. Children and adolescents often exhibit higher ALP levels as a natural part of rapid growth spurts due to active bone formation. During pregnancy, the placenta produces its own form of ALP, leading to a natural increase in the mother’s blood levels. A fatty meal before a blood test can also cause a temporary rise.
Interpreting Low Levels
While less common than elevated levels, a lower-than-normal alkaline phosphatase result can also indicate underlying health concerns. This scenario warrants medical attention. One notable cause is hypophosphatasia, a rare genetic disorder characterized by impaired bone mineralization, leading to fragile bones and dental problems. This condition directly involves a deficiency in the enzyme itself.
Severe nutritional deficiencies can also lead to reduced ALP levels. For instance, a lack of zinc, a cofactor for ALP, or a severe protein deficiency can impact the enzyme’s production or activity. Certain types of anemia, such as pernicious anemia, have been associated with lower ALP. Wilson’s disease, a rare inherited disorder that causes copper to accumulate in the body, can also manifest with low ALP. An underactive thyroid gland, or hypothyroidism, may also contribute to decreased ALP levels.
What to Do After an Abnormal Result
An abnormal alkaline phosphatase result from a blood test is a diagnostic clue, not a definitive diagnosis. It signals that further investigation may be necessary. Consult a doctor to discuss the findings and determine next steps. The doctor will consider symptoms, medical history, and other blood test results.
Other relevant blood tests often include liver function tests (e.g., ALT, AST, GGT), which can help differentiate between liver and bone sources of elevated ALP. If a bone issue is suspected, markers of bone turnover might also be checked. Based on these initial assessments, further diagnostic tests may be recommended. These could include imaging studies, such as an ultrasound, CT scan, or MRI, to visualize internal organs or bones. Avoid self-diagnosing based solely on an ALP result, as many factors can influence its levels. Treatment depends on accurately identifying the underlying cause of the abnormal ALP.