Intestinal Alkaline Phosphatase (IAP) Test
This test measures the amount of intestinal alkaline phosphatase, an enzyme made mainly by the cells that line your small intestine, in a sample of your blood.
{"Intestinal alkaline phosphatase (IAP) is an enzyme mainly made in your small intestine","This test helps doctors evaluate digestive system health and identify certain intestinal conditions","Abnormal results may indicate intestinal damage, inflammatory conditions, or other health issues","The test is performed on a blood sample (serum or plasma)","Results are typically reported as enzyme activity per volume"}
Key facts at a glance
- LOINC
- 71366-9
- Short code
- ALP-I
- Synonyms
- ALP Intest 3 SerPl-cCnc
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or plain red top tube
- Units
- not specified
- Ref low
- 0
- Ref high
- 25
- Critical range
- 20 not specified – 400 not specified
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 0 years
- Method
- Enzymatic assay using p-nitrophenyl phosphate (pNPP) substrate with heat inactivation or electrophoretic separation to isolate intestinal isoenzyme
- CPT
- 84075
- SNOMED
- 271544004
- Specimen volume
- 0.5-1.0 mL serum minimum; 1.5-2.0 mL preferred for complete panel
- Stability
- Room temperature: 24-48 hours; Refrigerated (2-8°C): 5-7 days; Frozen (-20°C): 2-3 months. 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 intestinal alkaline phosphatase (IAP) test measures the activity of a specific form of alkaline phosphatase enzyme that is primarily produced by the cells lining your small intestine. Alkaline phosphatase (ALP) is actually a group of enzymes that exist in different forms (isoenzymes) throughout the body, including the liver, bones, kidneys, and intestines. This particular test focuses on the intestinal variant.
Why is this test performed?
Your healthcare provider may order this test to help diagnose and monitor conditions affecting your intestines. It can be particularly useful when total alkaline phosphatase is elevated but the cause is unclear—distinguishing the intestinal form can help pinpoint whether the source is intestinal rather than hepatic (liver) or skeletal. The test may also be used to evaluate patients with suspected inflammatory bowel disease, intestinal infections, or certain malignancies involving the digestive tract.
How is the test performed?
A healthcare professional will collect a blood sample from a vein in your arm using a small needle. This sample is then sent to a laboratory where technicians measure the intestinal alkaline phosphatase activity. The procedure is quick and generally causes minimal discomfort. You do not need to fast for this specific test, though your doctor may instruct you to do so based on other tests being performed simultaneously.
Understanding your results
Normal reference ranges may vary depending on the laboratory and testing methods used. Elevated intestinal alkaline phosphatase levels may be associated with conditions such as inflammatory bowel disease (Crohn's disease, ulcerative colitis), intestinal infections, intestinal mucosal damage, malabsorption syndromes, or certain gastrointestinal cancers. Elevated levels may also occur in conditions associated with increased intestinal permeability or during recovery from intestinal injury. Your healthcare provider will interpret your results in the context of your overall health, symptoms, and other test findings.
Reference range
0-25 U/Lnot specified
Fasting preferred; intestinal ALP may rise after fatty meals
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Elevated intestinal alkaline phosphatase levels can indicate intestinal mucosal injury or inflammation. This marker may be particularly useful in assessing disease activity in inflammatory bowel disease (IBD), where levels may correlate with the extent of intestinal inflammation. The test may also aid in differentiating the source of elevated total alkaline phosphatase—when total ALP is high but intestinal IAP is normal, the elevation is more likely due to liver or bone involvement. Research has also explored IAP's role in maintaining intestinal barrier function and its potential anti-inflammatory properties, making it a subject of interest in gastroenterology.
Frequently asked questions
Do I need to fast before this test?
What can cause low intestinal alkaline phosphatase?
Is this test painful?
How long does it take to get results?
Are there any risks associated with this test?
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 17, 2026. · Read our editorial policy