Alkaline Phosphatase (ALP)
Alkaline phosphatase is an enzyme found in high concentrations in the liver (bile ducts), bones, kidneys, and intestines. In the liver, it is located in cells lining the bile ducts. ALP elevation is most commonly associated with bile duct obstruction or bone disorders. In growing children, ALP is normally 2–3x adult levels due to active bone growth.
Reference Ranges
Male
44 – 147
U/L
Female
44 – 147
U/L
Child
100 – 400
U/L
Ages 1–15, higher due to bone growth
Reference ranges may vary by laboratory. Always compare with the range printed on your lab report.
What Low Levels Mean
Low ALP is uncommon. Causes include zinc deficiency, malnutrition, hypothyroidism, pernicious anemia, and a rare genetic condition called hypophosphatasia. Low ALP is generally not a routine clinical concern.
What High Levels Mean
High ALP in adults suggests bile duct obstruction (gallstones, tumors), liver disease affecting bile flow, or bone disorders (Paget's disease, fractures, bone metastases). In children and adolescents, elevated ALP is normal during growth spurts. Pregnancy also raises ALP (placental source).
Frequently Asked Questions
Why is ALP high in children?
Growing bones produce large amounts of ALP. Children and adolescents normally have ALP levels 2–3 times higher than adults. This peaks during growth spurts (infancy and puberty) and gradually decreases to adult levels by age 18–20. A high ALP in a child is usually completely normal.
How can I tell if high ALP is from the liver or bones?
If ALT and AST are also elevated, the source is likely liver. If they are normal, bones are more likely. A GGT test can confirm — GGT rises with liver disease but not bone disease. Alternatively, ALP isoenzyme testing can directly identify the source.
Can medications cause high ALP?
Yes. Certain medications can elevate ALP, including some antibiotics, anti-seizure drugs (phenytoin), and cholesterol-lowering drugs. Herbal supplements can also cause elevation. Always share your medication list when liver enzymes are high.
This information is for educational purposes only and should not replace professional medical advice. Always consult your doctor for interpretation of your test results.
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