Alkaline Phosphatase (Heat Stable) Test
A blood test that measures the heat-stable portion of the alkaline phosphatase enzyme in your blood. This test helps your doctor determine whether elevated alkaline phosphatase levels come from liver or bone sources, so the underlying condition can be identified and treated appropriately.
{"Measures a specific form of alkaline phosphatase enzyme in your blood","Helps doctors distinguish between liver and bone-related conditions","Requires a simple blood draw, usually after fasting","Results help diagnose liver disease, bone disorders, or other conditions","Certain medications and conditions can affect test results"}
Key facts at a glance
- LOINC
- 32351-9
- Short code
- ALP-HL
- Synonyms
- ALP heat labile SerPl HS-cCnc
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or red top plain tube
- Units
- not specified
- Ref low
- 15
- Ref high
- 90
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–100 years
- Method
- heat-stability
- CPT
- 84075
- SNOMED
- 252965004
- Specimen volume
- 2-5 mL of venous blood
- Stability
- Room temperature: 2-3 days; Refrigerated (2-8°C): up to 7 days; Frozen (-20°C): 1 month; avoid repeated freeze-thaw cycles
- Hemolysis max
- 50
- Lipemia max
- 100
- Icterus max
- 20
- TAT
- 24–72 hours
- Order
- routine
What is this test?
The Alkaline Phosphatase (Heat Stable) test measures the amount of a specific enzyme called alkaline phosphatase in your blood. This test uses a special heat-stability method to identify different forms (isoenzymes) of the enzyme. The heat-labile portion comes primarily from liver cells, while the heat-stable portion comes from bones and other tissues. By measuring these separately, doctors can determine whether an elevated alkaline phosphatase level is due to liver problems or bone conditions.
Why is it ordered?
Your healthcare provider may order this test if a routine alkaline phosphatase test shows elevated levels. The heat stability test helps pinpoint the source: if the heat-labile (liver) fraction is high, it suggests liver disease or obstruction. If the heat-stable (bone) fraction is elevated, it may indicate bone disorders such as Paget's disease, osteomalacia, or bone healing after fractures. This test is particularly useful when the cause of elevated ALP is unclear from the total ALP measurement alone.
How to prepare for the test
Follow these preparation guidelines: Fast (no food or drink except water) for 8-12 hours before the test, as instructed by your healthcare provider. Inform your doctor about all medications you're taking, as some drugs can affect alkaline phosphatase levels. These include certain antibiotics, birth control pills, cholesterol medications, and drugs for diabetes or high blood pressure. Avoid alcohol before the test. If you're taking supplements containing biotin (vitamin B7), inform your provider as it may interfere with some test methods. The test is typically scheduled in the morning.
What to expect during the test
A healthcare professional will draw a small blood sample from a vein in your arm. The procedure takes only a few minutes. You may feel a brief sting or pinch when the needle is inserted. After the blood is collected, pressure is applied to the puncture site, and a bandage is placed. The sample is then sent to a laboratory for analysis. Results are usually available within a few days.
Understanding your results
Normal reference ranges vary by laboratory and depend on factors like age, sex, and the testing method used. Generally, adult values range from 20 to 140 U/L (units per liter), but this can vary. Elevated heat-labile ALP suggests liver conditions such as hepatitis, cirrhosis, bile duct obstruction, or gallstones. Elevated heat-stable ALP may indicate bone disorders including Paget's disease, osteomalacia, hyperparathyroidism, or bone cancer. Your doctor will interpret your results in context with your overall health, symptoms, and other test findings.
Reference range
15-90 U/Lnot specified
No special preparation or fasting required
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
This test is clinically significant because it helps differentiate between liver and bone as the source of elevated alkaline phosphatase, guiding further diagnosis and treatment. Elevated liver-origin ALP (heat-labile) may indicate cholestasis, liver inflammation, hepatitis, cirrhosis, or biliary obstruction. Elevated bone-origin ALP (heat-stable) may reflect increased bone turnover from conditions like Paget's disease, osteomalacia, hyperparathyroidism, or bone metastases. The test is also used to monitor treatment response in liver or bone diseases and to assess recovery after liver transplant or骨折 healing.
Normal or low alkaline phosphatase levels are less common but can occur in malnutrition, zinc deficiency, hypothyroidism, or certain genetic disorders. Combined with other liver function tests (ALT, AST, GGT, bilirubin), this test provides a comprehensive picture of liver health and helps rule out or confirm specific conditions.
Frequently asked questions
What's the difference between total Alkaline Phosphatase and the heat-stable test?
Do I need to fast before this test?
Can medications affect my test results?
What does a high heat-stable ALP mean?
What does a high heat-labile ALP mean?
Is the test safe?
How long does it take to get results?
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