Alkaline phosphatase (ALP) is an enzyme found throughout the body, playing a role in various bodily processes. As an enzyme, ALP accelerates chemical reactions and is involved in functions like metabolism within the liver and bone development. Its levels in the bloodstream can provide insights into overall health.
Understanding Alkaline Phosphatase
Alkaline phosphatase is present in all human tissues, with higher concentrations in specific organs. The liver, bile ducts, and bones are primary sources of ALP. Smaller amounts are also found in the intestines, kidneys, and, during pregnancy, the placenta. ALP assists in breaking down proteins and other organic compounds, which helps with digestion and nutrient absorption. It also contributes to mineral metabolism, particularly phosphorus and calcium, important for strong bone development.
Why Alkaline Phosphatase Levels Are Measured
Doctors measure ALP levels to screen for or help diagnose conditions affecting the liver or bones. An ALP test is often part of routine blood work, such as a comprehensive metabolic panel (CMP) or a liver panel, helping check for potential health issues even before symptoms appear.
A healthcare provider may also order an ALP test if a patient experiences symptoms suggesting liver damage or a bone disorder. Symptoms like nausea, vomiting, fatigue, or jaundice might indicate a liver problem. Bone pain, joint inflammation, or unusually shaped bones could prompt an ALP test to investigate bone health. The ALP test alone does not provide a definitive diagnosis, but it serves as an indicator of potential underlying health concerns.
Interpreting Elevated Alkaline Phosphatase Levels
An elevated ALP level indicates an underlying health issue. The normal range for adults is typically between 44 and 147 U/L, though this can vary by lab. Elevated levels often point to conditions affecting the liver or bones.
Liver-Related Causes
A noticeable increase in ALP levels may suggest a reduced or blocked flow of bile from the liver, known as cholestasis. This can occur due to gallstones, inflammation, or certain cancers. Liver conditions like hepatitis (inflammation of the liver), cirrhosis (scarring of the liver), or liver tumors can also lead to elevated ALP.
Bone-Related Causes
Increased ALP can be a sign of bone disorders due to increased bone cell activity. Conditions include:
Paget’s disease of the bone, a chronic disorder involving excessive bone breakdown and regrowth.
Osteomalacia, a softening of bones in adults often due to vitamin D deficiency.
Healing bone fractures.
Rapid bone growth in children and adolescents.
Bone cancers (osteogenic sarcoma or bone metastasis).
Other Causes
Less common causes of elevated ALP include certain cancers, chronic kidney disease, heart failure, and infections like mononucleosis. Certain medications, including some antibiotics, birth control pills, and antidepressants, can also cause ALP levels to rise. In pregnant individuals, ALP levels naturally increase significantly, primarily due to production from the placenta.
What Low Alkaline Phosphatase Levels Indicate
While less common than high levels, abnormally low ALP levels can also signal health concerns. A low ALP level might be associated with nutritional deficiencies, specifically zinc, magnesium, and vitamin B6, which are important for proper ALP production and activity.
Other potential causes include:
Hypophosphatasia, a rare inherited disorder affecting bone and tooth development.
An underactive thyroid (hypothyroidism).
Pernicious anemia.
Wilson’s disease, a rare condition causing copper buildup in tissues.
Certain medications, including oral contraceptives and some antibiotics.
Next Steps After Abnormal Results
If your ALP levels are abnormal, further diagnostic tests are typically necessary to determine the specific cause. An ALP test alone cannot identify the source of the enzyme. Your healthcare provider may order additional blood tests, such as liver function tests (e.g., AST, ALT, bilirubin, albumin) or gamma-glutamyl transferase (GGT) and 5′-nucleotidase tests, to help pinpoint whether the elevation originates from the liver or bones.
Imaging studies like an ultrasound, CT scan, or MRI of the liver and biliary system may be performed to check for obstructions or other liver pathologies. If a bone disorder is suspected, tests for calcium, phosphate, parathyroid hormone, and vitamin D levels might be conducted, potentially followed by bone scans. Discuss your results with a healthcare professional, as they can interpret the findings in the context of your overall health, symptoms, and medical history to develop an appropriate diagnosis and treatment plan.