Alkaline Phosphatase (ALP) Blood Test
The alkaline phosphatase (ALP) test measures the level of this enzyme in your blood to evaluate liver and bone health. ALP is found mainly in the liver, bile ducts, and bones, and abnormal levels can help your doctor detect liver problems, blocked bile ducts, or bone disorders early.
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Key facts at a glance
- LOINC
- 15015-1
- Short code
- ALP liver/total ratio
- Synonyms
- ALP Liver CFr SerPl
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST/gel tube) or plain red top tube
- Units
- not specified
- Ref low
- 40
- Ref high
- 129
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 0 years
- Method
- Photometric kinetic assay using para-nitrophenylphosphate (pNPP) substrate with isoenzyme separation
- CPT
- 84075
- SNOMED
- 27020006
- Specimen volume
- 0.5-1.0 mL serum minimum
- Stability
- Room temperature: 2-3 days; Refrigerated (2-8°C): 5-7 days; Frozen (-20°C): 2-3 weeks
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 4–24 hours
- Order
- routine
What is the Alkaline Phosphatase Test?
Alkaline phosphatase (ALP) is an enzyme found in various tissues throughout your body, with the highest concentrations in the liver, bile ducts, and bones. The ALP blood test measures the amount of this enzyme in your bloodstream. When liver cells are damaged or bile flow is blocked, ALP leaks into the blood, causing elevated levels. This test is commonly part of a comprehensive metabolic panel or liver function test panel.
How is the Test Performed?
A healthcare professional will draw a small blood sample from a vein in your arm. The sample is then sent to a laboratory for analysis. You typically do not need to fast before this test, though your doctor may instruct you otherwise if other blood tests are ordered at the same time.
Understanding Your Results
Normal ALP levels vary based on age, gender, and blood type. Generally, adult normal ranges are between 20 to 140 IU/L, but this can vary by laboratory. High ALP levels may indicate liver problems such as hepatitis, cirrhosis, or bile duct obstruction. Elevated ALP can also result from bone disorders like Paget's disease, bone fractures, or certain cancers. Low ALP levels are less common but may occur in malnutrition, zinc deficiency, or certain genetic disorders.
Factors That May Affect ALP Levels
Several factors can influence ALP results. Children and adolescents typically have higher ALP levels due to bone growth. Pregnant women, especially in the third trimester, may have elevated ALP from the placenta. Certain medications including some antibiotics, statins, and anti-seizure drugs can affect levels. Gallstones, liver infections, and bone diseases are common medical conditions that alter ALP readings.
Reference range
40-129 U/Lnot specified
No fasting or special preparation required
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
The ALP test helps diagnose and monitor liver diseases including hepatitis, cirrhosis, and bile duct obstruction. It can detect bone disorders such as Paget's disease, osteomalacia, and bone metastases. The test is valuable for monitoring the effectiveness of treatments for liver or bone conditions. When combined with other liver enzymes (ALT, AST, GGT, bilirubin), ALP helps pinpoint whether elevated levels stem from liver or bone origin.
Frequently asked questions
Do I need to fast before the ALP test?
What does a high ALP level mean?
What does a low ALP level mean?
Can ALP levels change during pregnancy?
How is ALP used with other tests?
Sources
- 1
- 2
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 10, 2026. · Read our editorial policy