Alkaline phosphatase (ALP) is an enzyme found in several tissues, especially the liver, bile ducts and bones. A high alkaline phosphatase therefore always raises the same first question: is it from the liver or the bones? The answer determines what the value means.
Below you will read how your doctor determines the source and which causes are most common.
What is alkaline phosphatase?
ALP is found in the liver, bile ducts, bones, intestines and placenta. Normal in adults is roughly 40 to 120 U/L, with differences per laboratory. Children and teenagers have physiologically higher values due to active bone growth, which is completely normal.
Liver or bone? How your doctor determines the source
The key is gamma-GT. If gamma-GT is also elevated alongside ALP, the source is almost certainly the liver or bile ducts. If gamma-GT is normal, a bone origin is more likely (Kwo et al., 2017). Sometimes a bone-specific ALP is measured additionally to confirm this.
Causes in the liver and bile ducts
With a liver cause, ALP usually fits the cholestatic pattern, where bile flow is obstructed:
- Gallstones blocking the bile duct
- Bile duct inflammation (cholangitis) or strictures
- Medication-induced bile stasis
- Liver tumours or metastases
If ALP and bilirubin rise together, that points to obstructed bile flow (Strassburg, 2010). Read more about the cholestatic pattern in understanding liver values.
Causes in the bones
- Healing bone fractures
- Paget's disease, in which bone remodelling is disrupted (Ralston, 2013)
- Severe vitamin D deficiency
- Bone growth in children and adolescents (physiological)
- Bone metastases
What can you do about a high alkaline phosphatase?
The approach depends entirely on the source. That is why the first step is determining whether it comes from the liver or the bones. Your doctor uses gamma-GT and possibly further investigation for this. Want to measure liver values including ALP? You can with the Vital Check liver function test, with review by a doctor.
Frequently asked questions
Is a high alkaline phosphatase always a liver problem?
No. ALP also comes from the bones. A normal gamma-GT makes a bone origin more likely, while an elevated gamma-GT points to the liver or bile ducts.
Why is my ALP high while my other liver values are normal?
That often fits a bone origin or an early bile duct problem. Your doctor can determine the source with gamma-GT and further investigation.
Do children have higher ALP values?
Yes, that is normal. Due to active bone growth, children and teenagers have physiologically higher ALP values than adults.
References
- Kwo PY, et al. ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries. American Journal of Gastroenterology. 2017. PubMed
- Ralston SH. Clinical practice. Paget's disease of bone. New England Journal of Medicine. 2013. PubMed
- Strassburg CP. Hyperbilirubinemia syndromes. Best Practice & Research Clinical Gastroenterology. 2010. PubMed
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