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Alkaline Phosphatase

Liver & Biliary

Alkaline phosphatase, serumAlk PhosALP

Review status

Currently under review

Pending specialist review and validation.

What it shows

Alkaline phosphatase (ALP) is an enzyme that helps break down phosphate compounds. It is produced mainly in the bile ducts of the liver and in bone-forming cells, and to a lesser extent in the intestine and placenta. The blood test measures the activity of ALP circulating in your bloodstream.

Because several tissues produce ALP, your level reflects both liver and bone processes. The test is often included in a liver panel or ordered on its own when your clinician wants to assess bile flow, liver structure, or bone turnover.

Why it matters

ALP is useful for detecting problems that reduce or block bile flow, such as gallstones, inflammation of the bile ducts, or certain liver conditions. It can also rise with bone growth, healing fractures, or disorders that increase bone remodeling.

Your clinician may order ALP if you have symptoms like jaundice, itching, dark urine, pale stools, right upper abdominal pain, or bone pain, or when other tests point toward a liver or bone source. It is commonly interpreted alongside tests like bilirubin, ALT, AST, and GGT to clarify the pattern of injury and decide on next steps.

During normal growth in children and teens, and in pregnancy, higher ALP can occur without disease. Understanding the context helps avoid unnecessary worry and guides appropriate evaluation.

Understanding your results

Interpreting ALP depends on your age, sex, pregnancy status, medications, and symptoms. If ALP is higher than expected, your clinician may add tests that help identify the source, such as GGT or ALP isoenzymes, and may consider imaging of the liver and bile ducts when a liver source is suspected.

Mild, isolated changes may simply be rechecked, especially if you recently had bone injury, dental or orthopedic procedures, or are growing. Persistent or larger changes usually prompt a search for liver or bone causes and treatment of the underlying issue.

Lower-than-expected ALP is less common and can be associated with nutrient deficiencies, endocrine conditions, or rare inherited disorders. Discuss any concerns with your clinician, who can put the result in context and recommend follow-up.

Reference ranges

77 – 237 U/L
Female
0 days – 15 days
77 – 237 U/L
Male
0 days – 15 days
116 – 450 U/L
Female
15 days – 1 year
116 – 450 U/L
Male
15 days – 1 year
135 – 320 U/L
Female
1 year – 10 years
135 – 320 U/L
Male
1 year – 10 years
122 – 400 U/L
Female
10 years – 13 years
122 – 400 U/L
Male
10 years – 13 years
52 – 243 U/L
Female
13 years – 15 years
109 – 449 U/L
Male
13 years – 15 years
46 – 110 U/L
Female
15 years – 17 years
77 – 317 U/L
Male
15 years – 17 years
41 – 82 U/L
Female
17 years – 18 years
50 – 142 U/L
Male
17 years – 18 years
42 – 98 U/L
Female
18 years – 60 years
53 – 128 U/L
Male
18 years – 60 years
53 – 141 U/L
Female
60 years – 150 years
56 – 120 U/L
Male
60 years – 150 years

Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.

Factors that could impact Alkaline Phosphatase

  • Age and growth

    Children and teens often have higher ALP because of active bone growth. Levels typically settle as growth slows in adulthood.

  • Pregnancy

    Placental ALP contributes to higher readings during pregnancy. Your clinician interprets results using pregnancy status and timing.

  • Medications and supplements

    Drugs such as anticonvulsants, some antibiotics, and estrogen-containing contraceptives can raise or occasionally lower ALP. Always share your full medication and supplement list.

  • Bone health and vitamin D

    Vitamin D deficiency, bone disorders, or healing fractures can increase ALP due to higher bone turnover. Treating the underlying issue often normalizes results.

  • Sample handling and collection tube

    Using EDTA or citrate tubes can falsely lower ALP by binding essential ions, and improper storage can alter activity. Labs use the correct tube and handling to ensure accuracy.

  • Recent procedures or intense activity

    Orthopedic surgery, dental work, or recent fractures can temporarily increase ALP. Let your clinician know about recent injuries or procedures.

2026

References

  1. McGill University Health Centre. (2015, July 02). Alkaline Phosphatase (Task CD 315848). Laboratory reference ranges.
  2. Kwo, P. Y., Cohen, S. M., & Lim, J. K. (2017). ACG clinical guideline: Evaluation of abnormal liver chemistries. The American Journal of Gastroenterology, 112(1), 18-35.
  3. Rifai, N., Horvath, A. R., & Wittwer, C. T. (Eds.). (2018). Tietz textbook of clinical chemistry and molecular diagnostics (6th ed.). Elsevier.