What Is the Alkaline Phosphatase (ALP) Test?
The alkaline phosphatase (ALP) test measures the level of this enzyme in your blood to evaluate your liver and bone health. ALP is a protein found in many tissues, with the highest amounts in the liver, bones, kidneys, and intestines. Your doctor may order this test during a routine checkup or if you have symptoms such as jaundice, abdominal pain, nausea, or unexplained bone pain. You may be asked to fast for 8-12 hours before the blood draw.
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Key facts at a glance
- LOINC
- 33421-9
- Short code
- ALP-OF
- Synonyms
- ALP Other SerPl-cCnc
- Category
- chemistry
- Sample
- serum
- Container
- SST (Serum Separator Tube) gold-top or red-top tube
- Units
- not specified
- Ref low
- 44
- Ref high
- 147
- Critical range
- 10 not specified – 500 not specified
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–120 years
- Method
- Spectrophotometry using p-nitrophenyl phosphate (pNPP) substrate at 405 nm
- CPT
- 84075
- SNOMED
- 270000006
- 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 months
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 1–24 hours
- Order
- routine
What is the Alkaline Phosphatase Test?
Alkaline phosphatase (ALP) is an enzyme—a type of protein that speeds up chemical reactions—in your body. It is found in many tissues, with the highest concentrations in the liver, bones, kidneys, and intestines. The ALP blood test measures how much of this enzyme is circulating in your bloodstream.
Why is This Test Performed?
Your healthcare provider may order an ALP test as part of a routine health check or if you have symptoms such as jaundice (yellowing of the skin or eyes), abdominal pain, nausea, or unexplained bone pain. The test helps doctors assess how well your liver and biliary system are functioning, or whether there may be a bone disorder.
How is the Test Done?
A healthcare professional will draw a small sample of blood from a vein in your arm using a needle. The blood is collected into a tube and sent to a laboratory for analysis. You may be asked to fast (not eat or drink) for 8-12 hours before the test, as instructed by your doctor. The procedure only takes a few minutes.
Understanding Your Results
Normal ALP levels vary depending on age, sex, and blood type. Generally, the normal range is about 20 to 140 IU/L (international units per liter), but this can differ by laboratory. Your doctor will interpret your results in context with your overall health and other test results.
Reference range
44-147 U/Lnot specified
No fasting or special preparation required
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Elevated ALP levels may indicate: Liver conditions such as hepatitis, cirrhosis, or bile duct obstruction; Bone disorders including Paget's disease, osteomalacia, or bone metastases; Gallbladder disease; Certain medications or supplements; Pregnancy (due to placental ALP).
Low ALP levels are less common but can be caused by: Malnutrition or zinc deficiency; Hypothyroidism; Wilson's disease; Certain genetic disorders; Severe liver disease.
To determine the exact cause of abnormal ALP levels, doctors often order additional tests, such as gamma-glutamyl transferase (GGT), bilirubin, or imaging studies of the liver or bones.
Frequently asked questions
Do I need to fast before the ALP test?
Is the test painful?
How long does it take to get results?
Can medications affect ALP levels?
What happens if my ALP is high?
Sources
- 1
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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