Blood and lab tests
What Does Alkaline Phosphatase (ALP) Mean?
Alkaline phosphatase · say it: AL-kuh-line FOS-fuh-taysAlso written: ALP, alk phos, alkaline phos
Short answer
Alkaline phosphatase (ALP) is an enzyme found mostly in the liver, bile ducts and bones, measured on liver blood tests.
What it means
Alkaline phosphatase, usually shortened to ALP, is an enzyme. Enzymes are proteins that speed up chemical reactions in the body. ALP is found in many tissues, but most of the ALP in the blood comes from the liver, the bile ducts and the bones. Smaller amounts come from the gut and, during pregnancy, the placenta.
ALP is part of liver function tests and the comprehensive metabolic panel. A raised ALP can mean bile is not flowing freely, or that bone is being built or remodelled faster than usual. To tell which source it comes from, doctors often look at GGT: if GGT is also up, the liver or bile ducts are more likely. Growing children and teenagers naturally have higher ALP, so many labs print age-based ranges.
ALP is different from ALT and AST, the other liver enzymes on the same report. ALT and AST mostly reflect the liver cells themselves, while ALP is more linked to the bile ducts and to bone.
Where you may see it
- Liver function tests, listed as "ALP" or "Alk Phos"
- Comprehensive metabolic panels
- Bone clinic letters about conditions such as Paget's disease of bone
📄 How it looks on a report
ALP 168 U/L H
🙅 What it does not mean
- A high ALP does not automatically point to the liver. Bone growth, a healing fracture, low vitamin D and pregnancy can all raise it.
- A teenager's ALP above an adult range is often expected. Growing bones release more of the enzyme, which is why age matters when reading it.
- ALP is not a test of how well the liver works. It hints at where there may be activity or blockage, and other tests help explain it.
🗒️ Questions to ask your doctor
🧾 Reports where you will see “Alkaline phosphatase”
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🔗 Read more from trusted sources
- “Alkaline phosphatase” on MedlinePlus ↗
US National Library of Medicine
- MedlinePlus lab test guides ↗
US National Library of Medicine
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