Alkaline Phosphatase (ALP) Blood Test
The alkaline phosphatase (ALP) test is a simple blood test that measures the level of an enzyme called alkaline phosphatase in your blood. This enzyme is naturally found in many tissues throughout your body, with the highest concentrations in your liver, bones, and intestines, and smaller amounts in your kidneys. Because ALP comes mainly from the liver and bones, this test helps your doctor check how well these organs and tissues are working and can help detect liver disease, bile duct blockages, or bone conditions early.
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Key facts at a glance
- LOINC
- 15018-5
- Short code
- ALP renal/total ratio
- Synonyms
- ALP Renal CFr SerPl
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or plain red top tube
- Units
- not specified
- Ref low
- 44
- Ref high
- 147
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–120 years
- Method
- Spectrophotometry with enzymatic assay for alkaline phosphatase isoforms
- CPT
- 84075
- SNOMED
- 31311007
- Specimen volume
- 2-5 mL of venous blood
- Stability
- Serum stable for up to 7 days at 2-8°C; for longer storage, freeze at -20°C or below
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 4–24 hours
- Order
- routine
What is Alkaline Phosphatase?
Alkaline phosphatase (ALP) is an enzyme—a type of protein that helps speed up chemical reactions in your body. It is found in many tissues throughout the body, with the highest concentrations in the liver, bones, intestines, and kidneys. The ALP in your blood comes primarily from the liver and bones.
Why is This Test Done?
The ALP test is typically part of a comprehensive metabolic panel or liver function tests. Your doctor may order this test to: check for liver disease or damage, evaluate bone disorders such as Paget's disease or bone cancer, investigate the cause of jaundice (yellowing of skin and eyes), monitor the effectiveness of treatment for liver or bone conditions, or as part of a routine health checkup.
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 for analysis. You do not need to fast before this test unless your doctor instructs otherwise. The procedure is quick and generally causes minimal discomfort.
Understanding Your Results
Normal ALP levels vary by age, sex, and blood type. Generally, adult normal ranges are between 20 to 140 U/L (units per liter), though reference ranges may differ between laboratories. Your doctor will interpret your results in context with other liver tests and your overall health condition.
Factors That May Affect ALP Levels
Several factors can influence ALP levels: Age and growth spurts in children and adolescents cause naturally higher levels, certain medications including some antibiotics, cholesterol-lowering drugs, and anticonvulsants, pregnancy especially in the third trimester, blood type (people with blood types B or O may have slightly higher levels), and recent bone fractures or healing.
Reference range
44-147 U/Lnot specified
No special preparation or fasting required
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Elevated ALP levels (hyperphosphatasemia) may indicate: Liver problems such as hepatitis, cirrhosis, bile duct obstruction, or liver tumors, Bone disorders including Paget's disease, osteomalacia, rickets, or bone cancer, Gallbladder disease, certain infections, or heart failure. Moderately elevated ALP is common in children due to bone growth and in pregnant women.
Low ALP levels (hypophosphatasemia) are less common but may be associated with: Malnutrition or zinc deficiency, Hypothyroidism, Wilson's disease (a rare copper overload disorder), Certain medications, or Rare genetic conditions such as hypophosphatasia.
When ALP is abnormal, doctors often order additional tests—such as gamma-glutamyl transferase (GGT) or bilirubin—to help determine whether the elevated source is liver or bone-related. The pattern of elevation, along with other liver enzyme results, helps pinpoint the underlying cause.
Frequently asked questions
Do I need to fast before the ALP test?
Is the test dangerous?
Why would my doctor order just the ALP test?
Can high ALP mean cancer?
Why are children's ALP levels higher?
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