Alkaline Phosphatase (ALP) Isoenzyme Test
A blood test that measures the different forms, called isoenzymes, of the alkaline phosphatase enzyme in your blood. When your overall ALP level is high, this test helps your doctor pinpoint whether the excess enzyme is coming from your liver, bones, intestines, or kidneys, which supports an accurate diagnosis of liver disease, bone disorders, or other conditions and helps guide the right treatment plan for you.
{"Measures specific types of alkaline phosphatase (ALP) in your blood","Helps distinguish between bone and liver sources of elevated ALP","Used to diagnose liver disease, bone disorders, or other conditions","Simple blood test requiring no special preparation","Results help your doctor determine the cause of symptoms"}
Key facts at a glance
- LOINC
- 53524-5
- Short code
- ALP bile/total ratio
- Synonyms
- ALP Bile CFr SerPl
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST/Gel tube) or plain red top tube
- Units
- not specified
- Ref low
- 0
- Ref high
- 0.4
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 0 years
- Method
- Spectrophotometric colorimetric assay using p-nitrophenyl phosphate substrate
- CPT
- 84075
- SNOMED
- 271427004
- Specimen volume
- 1.0-2.0 mL of serum minimum
- Stability
- Room temperature: 24-48 hours; Refrigerated (2-8°C): 5-7 days; Frozen (-20°C): 2-3 months. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 1–24 hours
- Order
- routine
What is this test?
The alkaline phosphatase (ALP) isoenzyme test measures different forms of the ALP enzyme in your blood. ALP is an enzyme found in various tissues throughout your body, particularly in the liver, bones, intestines, and kidneys. This test helps determine which tissue is producing excess ALP when levels are elevated.
Why is it important?
When your total ALP level is high, it indicates a problem somewhere in your body, but it doesn't tell your doctor exactly where. By measuring the specific isoenzymes (bone ALP vs. liver ALP), this test helps pinpoint whether the elevated ALP is due to liver disease, bone disorders, or other conditions. This information is crucial for accurate diagnosis and appropriate treatment.
How is the test performed?
A healthcare professional will draw a small blood sample from a vein in your arm. The blood is collected in a tube and sent to a laboratory for analysis. The procedure takes only a few minutes and is generally well-tolerated with minimal discomfort.
How to prepare
Follow your doctor's instructions regarding fasting or medication adjustments. Typically, you may need to fast for 8-12 hours before the test. Inform your doctor about all medications, supplements, or vitamins you are taking, as some substances can affect ALP levels.
Reference range
0.00-0.40 (fraction)not specified
Fasting specimen preferred to minimize contribution from intestinal ALP isoenzyme
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Elevated liver ALP isoenzyme may indicate: hepatitis, cirrhosis, bile duct obstruction, gallstones, or liver tumors. Elevated bone ALP isoenzyme may indicate: bone diseases (Paget's disease), bone healing after fractures, hyperparathyroidism, osteomalacia, or certain cancers that affect bone. This test is particularly valuable when total ALP is elevated but the cause is unclear, helping differentiate between hepatic and skeletal sources.
Abnormal results should always be interpreted in conjunction with your clinical symptoms, medical history, and other test results. Your healthcare provider will discuss what your specific results mean for your health condition.
Frequently asked questions
Is this test painful?
How long does it take to get results?
What can affect my ALP levels?
Do I need to do anything after the test?
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