Explainer · updated 2026-11-09
Alkaline phosphatase, explained in plain English
Key facts
- Typical adult reference interval: 30-120 U/L (ABIM)
- What alkaline phosphatase is: an enzyme that comes from the bile ducts and from bone in roughly equal measure (ACG 2017)
- What a high level usually points at: the bile ducts or bone, rather than the liver cells themselves (ACG 2017)
- What a persistently low figure follows: some medicines, malnutrition or a mineral shortage (ACG 2017)
What it is
Alkaline phosphatase is an enzyme that comes from the bile ducts and from bone in roughly equal measure. When it is raised, the next question is which of the two it came from. The GGT beside it usually answers that. It is measured in the blood.
What the number is telling you
The level is read beside GGT, ALT and AST. Growing bone and healing bone raise it, which is why a single high reading is usually repeated before it is read as a problem.
What high or low can mean
High: A high level usually points at the bile ducts or at bone rather than at the liver cells themselves. When it climbs while ALT and AST stay near normal, the pattern points to a bile-flow problem rather than cell damage.
Low: A persistently low figure follows some medicines, and malnutrition or a mineral shortage can do it too.
What a typical result looks like
Typical adult reference intervals from ABIM run from 30 to 120 U/L. The range on your own report is the one that counts.
Questions worth asking your doctor
- Does my GGT suggest a liver or a bone source?
- Could growth or healing bone explain this?
- Which medicines could affect it?
- How does this compare with my previous results?
If a result worries you, ask your doctor.
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