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Alkaline phosphatase (ALP)
An enzyme of liver, bile ducts, and bone; the source of a high value needs a second look.
Other names: Alkaline phosphataseSection: Blood chemistry
Updated: August 29, 2026·MedProtect editorial team Reference information — not a diagnosis or a prescription
In shortA common adult reference range is 40–129 IU/L. High values come from the liver or from bone; children in growth spurts and pregnant women run higher normally.
Reference ranges
Group
Reference range
Adults
40–129 IU/L
Normal values vary slightly between laboratories, and they vary with age and sex. High levels are normal in children during growth spurts and in pregnant women.
Check your value
Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.
A rough comparison with a typical range, not a diagnosis. Reference ranges vary between laboratories — check the range on your own report and let a clinician interpret the result.
What this marker is
Alkaline phosphatase (ALP) is a protein found in all body tissues, with the highest amounts in the liver, the bile ducts, and bone. A blood test measures the total level, and the result is reported in international units per liter (IU/L).
The liver and bone produce different types of ALP, but the standard test cannot tell them apart. When ALP is high, the next step is either an ALP isoenzyme test — which identifies which tissue is making it — or the other liver function tests: if those are high too, the liver is the likely source.
Some high values are entirely normal. Children going through growth spurts and pregnant women normally show higher ALP, and even a fatty meal can raise the level in people with blood type O or B. A result outside the range therefore does not automatically mean disease.
Blood is drawn from a vein, usually from the inside of the elbow. Many medicines can interfere with the result, so the provider will say whether any of them should be paused before the draw — and none should be stopped without that conversation.
When it is high
Blocked bile ductsA blockage in the bile ducts is a classic liver-side cause of high ALP.
Cirrhosis and hepatitisScarring or inflammation of the liver raises the liver type of ALP. Mononucleosis, which can swell the liver, appears here too.
Paget's disease of boneThis bone disorder makes bones unusually large and weak and is a typical bone-side cause of a high ALP.
Healing fracture or bone tumorsActive bone repair after a fracture, osteoblastic bone tumors, and osteomalacia all release the bone type of ALP.
Normal, non-disease causesGrowth spurts in children, pregnancy, and a fatty meal in people with blood type O or B raise ALP without any illness.
Moderate risesHodgkin lymphoma, heart failure, and certain infections can produce a moderately high level.
When it is low
Zinc or protein deficiency, malnutritionToo little zinc, too little protein, and general malnutrition can push ALP below the range.
Pernicious anemiaThis B12-related anemia is one of the listed causes of a low ALP.
Thyroid disease and Wilson diseaseAn underactive thyroid and the copper-handling disorder Wilson disease can both lower ALP.
HypophosphatasiaA rare genetic disease that affects bones and teeth produces unusually low ALP levels.
What can skew the result
These factors can shift the value without any disease — worth considering before a retest:
PregnancyGrowth spurts in childrenA fatty meal (blood type O or B)Many medicines
How to prepare
Many medicines can interfere with the result. Your provider will tell you if any medicine should be paused before the test; do not stop or change medicines on your own.
When a retest makes sense
A high ALP is followed by tests that find its source: the liver function panel, an ALP isoenzyme test where available, and the comparison with GGT that separates liver from bone.
Who usually reviews this result
A result outside the reference range is usually reviewed by: your GP or primary care doctor; a gastroenterologist or a bone specialist (endocrinologist or orthopedist) depending on the suspected source. Bring your lab report and any previous results to the appointment.
Names used on lab reports
Your report may use any of these names: ALPALKPHOSAlkpALK PHOSAlkaline phosphatase
Units
Measured in: IU/L
Several markers on your report?
See how MedProtect explains results in the app: the whole report, a check of the recognized values, and a clear breakdown.
The provider looks for the source. If the other liver tests are also high, the liver is the likely origin; if they are normal, a bone disorder moves up the list. An ALP isoenzyme test can identify the tissue directly, but it is not available everywhere.
Is high ALP normal in pregnancy?
Yes. Pregnant women normally show higher ALP, as do children during growth spurts. A high value in these situations is expected and is read differently.
What does low ALP mean?
Low ALP is less common than high. The listed causes include zinc deficiency, protein deficiency, malnutrition, pernicious anemia, thyroid disease, Wilson disease, and the rare genetic condition hypophosphatasia.
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