Alkaline Phosphatase (ALP) Heat Stability Test
The Alkaline Phosphatase (ALP) heat stability test measures different forms of ALP in your blood to help distinguish liver disease from bone disease. A healthcare professional draws a small blood sample from a vein in your arm and sends it to a laboratory, where the sample is heated to 56°C (132.8°F). This inactivates heat-labile, liver-derived ALP while bone-derived ALP remains stable. Comparing ALP levels before and after heating helps determine whether an elevated result is more likely related to the liver or bones. Your doctor may order this test after a chemistry panel shows high total ALP, especially if you have symptoms such as jaundice, abdominal pain, dark urine, bone pain, fractures, or deformities. You typically do not need to fast, but you should follow your healthcare provider’s instructions and tell the provider about all medications and supplements you take. High ALP can reflect liver or bone problems, while low ALP may occur with malnutrition, zinc deficiency, hypothyroidism, certain genetic conditions, or blood transfusions. Results should be interpreted with your symptoms, other laboratory tests, age, pregnancy status, bone injuries or surgery, medications, and other relevant factors.
{"Measures heat-labile ALP (primarily from liver) and total ALP to identify disease source","Elevated liver ALP suggests bile duct problems, liver disease, or certain medications","Elevated bone ALP indicates increased bone activity from healing fractures, Paget's disease, or bone cancers","The heat stability test helps differentiate between liver and bone causes of elevated ALP","Normal results vary by age and gender, with higher levels in growing children and pregnant women"}
Key facts at a glance
- LOINC
- 42718-7
- Short code
- ALP heat stable
- Synonyms
- ALP heat labile CFr SerPl HS
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST/gold top) or red top plain tube
- Units
- not specified
- Ref low
- 20
- Ref high
- 40
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–120 years
- Method
- heat-stability
- CPT
- 84075
- SNOMED
- 31309007
- Specimen volume
- 1.0-2.0 mL serum minimum
- Stability
- Room temperature: 2-3 days; Refrigerated (2-8°C): 5-7 days; Frozen (-20°C or below): 2-3 months. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 4–24 hours
- Order
- routine
What is this test?
The Alkaline Phosphatase (ALP) heat stability test measures two forms of ALP in your blood: heat-labile ALP (which comes mainly from the liver) and total ALP (which includes both liver and bone sources). By applying heat to the blood sample, the liver-derived ALP becomes inactive (heat-labile), while bone-derived ALP remains stable. This helps doctors determine whether an elevated ALP level is due to liver disease or bone disease.
How is the test performed?
A healthcare professional will draw a small blood sample from a vein in your arm. The sample is then sent to a laboratory where it is heated to 56°C (132.8°F) for a specific time. This heat treatment inactivates the liver form of ALP but not the bone form. By comparing ALP levels before and after heating, laboratory technicians can determine how much ALP comes from the liver versus the bones.
Why might I need this test?
Your doctor may order this test if a routine chemistry panel shows an elevated total ALP level and they need to determine the cause. This test is particularly useful when symptoms suggest either liver/biliary disease (such as jaundice, abdominal pain, or dark urine) or bone disease (such as bone pain, fractures, or deformities).
Reference range
Interpretive only (no fixed adult range; typically ~0.4-0.8 fraction; >0.80 suggests bone origin)not specified
No special preparation required
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Elevated heat-labile ALP (high proportion of liver-derived ALP) suggests: gallstones or bile duct obstruction, hepatitis or cirrhosis, liver tumors or metastases, certain medications that affect liver function, or primary biliary cholangitis. Elevated bone ALP (high proportion remaining after heat treatment) suggests: bone healing after fractures, Paget's disease of bone, osteomalacia or rickets, bone cancers or metastases, hyperparathyroidism, or normal growth in children and adolescents. Normal results typically show that most ALP is heat-labile (liver origin), with only small amounts from bone. The interpretation should always be made by your healthcare provider in context with your symptoms and other test results.
Frequently asked questions
Do I need to fast before this test?
What do high ALP levels mean?
Can ALP levels be normal with liver disease?
Are there factors that can affect ALP results?
What happens if my ALP is low?
Sources
- 1
- 2
- 3
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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