Alkaline Phosphatase (ALP) Isoenzyme Test
A blood test that measures the different forms of the alkaline phosphatase enzyme in your blood, helping your doctor identify which tissue in your body, such as the liver or bones, is producing elevated levels.
{"Measures different forms (isoenzymes) of alkaline phosphatase from liver, bone, intestines, and placenta","Helps doctors determine whether elevated ALP comes from liver disease or bone disorders","Involves a simple blood draw; results typically available within 1-2 days"}
Key facts at a glance
- LOINC
- 12805-8
- Short code
- ALP ISO
- Synonyms
- ALP Iso SerPl-aCnc
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or red top tube
- Units
- not specified
- Ref low
- 44
- Ref high
- 147
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 0 years
- Method
- Electrophoresis or immunoassay for isoenzyme separation
- CPT
- 84080
- SNOMED
- 270000006
- Specimen volume
- 2-5 mL whole blood
- Stability
- Room temperature: 7 days; Refrigerated (2-8°C): 7-14 days; Frozen (-20°C): stable for months. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 24–72 hours
- Order
- routine
What is this test?
Alkaline phosphatase (ALP) is an enzyme found in various tissues throughout your body, including the liver, bones, intestines, kidneys, and placenta. The ALP isoenzyme test measures the specific forms of this enzyme to help determine which tissue is producing excess ALP. This is important because elevated ALP levels can result from different conditions, and knowing the source helps your doctor make an accurate diagnosis.
Why do I need this test?
Your doctor may order this test if a routine blood test shows elevated ALP levels. The isoenzyme test helps differentiate between liver disease and bone disorders, as both conditions can cause increased ALP. It is commonly used to diagnose and monitor conditions such as hepatitis, cirrhosis, bile duct obstruction, Paget's disease, bone cancer, or osteomalacia. The test may also be ordered to evaluate unexplained bone pain or liver function abnormalities.
How is the test performed?
A healthcare professional will collect a blood sample from a vein in your arm using a small needle. You may feel a brief stinging sensation when the needle is inserted or removed. The blood sample is then sent to a laboratory where specialists analyze the different isoenzyme forms. The procedure typically takes only a few minutes, and you can resume normal activities immediately afterward.
How to prepare for the test
In most cases, no special preparation is required for the ALP isoenzyme test. You may be asked to fast (not eat or drink) for a short period if other blood tests are being done at the same time. Always follow your doctor's specific instructions. Inform your healthcare provider about all medications, vitamins, and supplements you are taking, as some drugs can affect ALP levels.
Understanding your results
Your test results will show the levels of different ALP isoenzymes, typically categorized as liver ALP, bone ALP, intestinal ALP, and sometimes placental ALP (during pregnancy). Elevated liver ALP suggests liver or biliary tract problems. Elevated bone ALP indicates increased bone activity, which may occur in bone diseases or during fracture healing. Your doctor will interpret these results together with your other lab tests and medical history to determine the cause of the abnormal findings.
Reference range
Liver: 0-94 U/L; Bone: 0-90 U/L; Intestinal: 0-18 U/L (method-dependent)not specified
Fasting preferred (8-12 h) to minimize intestinal isoenzyme contribution
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
The ALP isoenzyme test has significant clinical value in differential diagnosis. Elevated liver ALP isoenzymes may indicate conditions such as hepatitis, cirrhosis, gallstones, bile duct obstruction, or liver tumors. Elevated bone ALP isoenzymes are associated with Paget's disease, osteomalacia, rickets, bone metastases, hyperparathyroidism, or healing fractures. The test helps healthcare providers avoid misdiagnosis and guide appropriate treatment by precisely identifying the source of enzyme elevation.
Frequently asked questions
Does this test require fasting?
Is the test painful?
How long does it take to get results?
Can medications affect my ALP levels?
Is elevated ALP always a sign of disease?
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