Alkaline phosphatase
An enzyme that comes from your bones and from your bile ducts.
Also printed asALP · Alk Phos · AP
What it measures
An enzyme from the bile ducts of the liver and from bone.
Rises when bile is not draining freely or when bone is turning over quickly, so it points to two very different systems.
Why it matters for how long you stay well
Read with vitamin D and calcium it can point to bone that is not being rebuilt properly, and bone strength in your fifties decides how independent you are in your eighties.
How it shows up in daily life
Because it has two homes, a raised level asks a question rather than answering one: bone or bile.
High and low readings
When it reads high
Bile flow or bone turnover; also normal in growing teenagers.
When it reads low
Low zinc or magnesium sometimes.
What moves it
Daily life
- low vitamin D, which lifts it
- bone healing after a fracture
- pregnancy
- alcohol
Medicines known to shift it
- oral contraceptives (can raise it)
- antibiotics (can raise it)
- vitamin D supplements (lower it when vitamin D was low)
Listed so a result can be read in context. It is not advice to start, stop or change any medicine; that decision belongs with your physician.
Common questions
What does Alkaline Phosphatase measure?
An enzyme from the bile ducts of the liver and from bone. Rises when bile is not draining freely or when bone is turning over quickly, so it points to two very different systems.
What does a high Alkaline phosphatase result usually mean?
Bile flow or bone turnover; also normal in growing teenagers.
What does a low Alkaline phosphatase result usually mean?
Low zinc or magnesium sometimes.
What is the usual reference range for Alkaline phosphatase?
A broad adult reference band is 40–129 U/L. For women the band is 35–104 U/L. Labs differ, so read your result against the band printed on your own report.
Educational only, not a diagnosis. A single number means little without your history and the rest of your panel, so discuss your own results with your physician.
Typical adult reference band
- Men
- 40–129 U/L
- Women
- 35–104 U/L
Labs differ. The band printed on your own report is the one that applies to your result.
Reported in U/L
Ageing relevance
5/5
A direct input to a validated biological-age algorithm.
One of the nine blood inputs to the PhenoAge biological-age clock (Levine et al., Aging, 2018).
Worth knowing
Children and teenagers run much higher levels than adults, because their bones are still growing.
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