Alkaline Phosphatase Isoenzymes Test
The Alkaline Phosphatase Isoenzymes test measures different forms, or isoenzymes, of the alkaline phosphatase enzyme in your blood. Alkaline phosphatase, also called ALP, is found in many body tissues, including the liver, bones, intestines, and kidneys. This test uses the enzyme’s heat stability to help identify whether elevated ALP comes from the liver, gallbladder, or bones, which can help your doctor diagnose the underlying condition and guide treatment.
{"The test identifies the source of elevated alkaline phosphatase (bone vs. liver)","Different isoenzymes are produced by different organs including liver, bone, and intestines","The heat stability method helps distinguish between bone and liver origins","Commonly used to diagnose bone disorders or liver/gallbladder diseases","A simple blood test with no special preparation typically required"}
Key facts at a glance
- LOINC
- 16182-8
- Short code
- ALP-ISO
- Synonyms
- ALP Isos SerPl HS-cCnc
- Category
- chemistry
- Sample
- serum
- Container
- SST (serum separator tube) or red top glass tube
- Units
- not specified
- Ref low
- 20
- Ref high
- 50
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–120 years
- Method
- heat-stability
- CPT
- 82050 (for ALP total; isoenzyme analysis may require separate billing)
- SNOMED
- 270880006
- Specimen volume
- 1-2 mL serum minimum
- Stability
- Room temperature: 7 days; Refrigerated (2-8°C): 7 days; Frozen (-20°C): 30 days. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 24–72 hours
- Order
- routine
What is this test?
The Alkaline Phosphatase Isoenzymes test measures different forms (isoenzymes) of the alkaline phosphatase enzyme in your blood. Alkaline phosphatase (ALP) is an enzyme found in many tissues throughout your body, including the liver, bones, intestines, and kidneys. This specific test uses heat stability to determine which organ is producing the enzyme.
Why do I need this test?
Your doctor may order this test if a routine alkaline phosphatase test shows elevated levels. The isoenzyme test helps determine whether the high ALP is due to: bone conditions (such as Paget's disease, osteoporosis, or bone healing), liver or gallbladder diseases (such as hepatitis, cirrhosis, or gallstones), or other less common causes. This differentiation is crucial for proper diagnosis and 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 into a tube and sent to a laboratory for analysis. In the lab, the sample is heated to a specific temperature - bone isoenzymes are more heat-sensitive and break down faster than liver isoenzymes. By measuring how much enzyme activity remains after heating, technicians can determine the proportion coming from bone versus liver.
What do the results mean?
Results typically show the percentage or activity level of different isoenzymes. Elevated liver isoenzymes may indicate liver disease, gallstones, or bile duct obstruction. Elevated bone isoenzymes may suggest bone disorders, bone healing after fractures, or certain cancers that affect bone. Your doctor will interpret these results along with other tests and your medical history to make an accurate diagnosis.
Reference range
Method-dependent; typically 20-50 U/L residual heat-stable activity (or 25-55% of total ALP)not specified
No fasting or special preparation required
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
The Alkaline Phosphatase Isoenzymes test is valuable for distinguishing between liver and bone as the source of elevated alkaline phosphatase. Liver ALP (ALP-1) elevations are seen in conditions such as hepatitis, cholestasis, cirrhosis, and gallstones. Bone ALP (ALP-2) elevations occur in Paget's disease, osteomalacia, hyperparathyroidism, and during bone healing. This test helps avoid unnecessary procedures by correctly identifying the affected organ system.
Frequently asked questions
Do I need to fast before this test?
Are there any risks with this blood test?
How long does it take to get results?
Can medications affect my test results?
What happens if my results are abnormal?
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