Fecal Immunochemical Test (FIT) for Colorectal Cancer Screening
A test that measures 5-hydroxyindoleacetate (5-HIAA), a breakdown product of serotonin, in a 24-hour urine collection to help diagnose neuroendocrine tumors.
{"Measures serotonin breakdown product in 24-hour urine collection","Primarily used to diagnose and monitor carcinoid tumors","Requires dietary and medication restrictions before the test","Abnormal results may indicate a neuroendocrine tumor","Follow collection instructions carefully for accurate results"}
Key facts at a glance
- LOINC
- 1695-6
- Short code
- 5HIAA24
- Synonyms
- 5OH-indoleacetate 24h Ur-mRate
- Category
- chemistry
- Sample
- urine
- Container
- 24-hour urine collection container with appropriate preservative (typically hydrochloric acid or acetic acid) to maintain specimen stability
- Units
- N/A
- Ref low
- 2
- Ref high
- 9
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 0 years
- Method
- High Performance Liquid Chromatography (HPLC) with electrochemical detection or mass spectrometry
- CPT
- 83498
- SNOMED
- 269687004
- Specimen volume
- Complete 24-hour collection; aliquot typically 10-20 mL for analysis
- Stability
- Room temperature: 24-48 hours; Refrigerated (2-8°C): 5-7 days; Frozen (-20°C): several weeks. Maintain acidic pH throughout collection.
- Hemolysis max
- 0
- Lipemia max
- 0
- Icterus max
- 0
- TAT
- 48–168 hours
- Order
- routine
This test is a simple stool-based screening test called the fecal immunochemical test, or FIT. It checks your bowel movement for hidden (occult) blood that you cannot see, which can be an early warning sign of colorectal cancer or precancerous polyps in the colon or rectum.
The 5-HIAA (5-hydroxyindoleacetate) urine test measures the amount of this substance in your urine over a 24-hour period. 5-HIAA is a byproduct created when your body breaks down serotonin, a hormone and neurotransmitter. This test helps doctors evaluate whether your body is producing abnormal amounts of serotonin, which can indicate certain types of tumors.
You need this test because finding colorectal cancer early, before symptoms appear, makes treatment much more effective. Screening is recommended for most adults starting at age 45, and detecting precancerous polyps through a FIT test can help prevent cancer from developing at all.
Your doctor may order this test if they suspect you have a carcinoid tumor or other neuroendocrine tumor. These tumors can produce excess serotonin, leading to elevated 5-HIAA levels in your urine. Symptoms that might prompt testing include facial flushing, diarrhea, abdominal cramping, wheezing, or heart valve problems. The test is also used to monitor treatment effectiveness if you've already been diagnosed with a carcinoid tumor.
Collect the sample at home using the kit provided. Pass a bowel movement normally, then use the brush or stick from the kit to take a small smear of stool and apply it to the collection card or tube as directed. Avoid letting the sample touch urine or toilet water, close the container tightly, write your name and the date on the label, and return or mail it to the lab within the time frame listed in the instructions.
For a 24-hour urine collection: (1) On the collection day, start by urinating into the toilet upon waking up. (2) For all subsequent urinations over the next 24 hours, collect the urine in the provided container. (3) Keep the container refrigerated or in a cool place. (4) Collect all urine during the 24-hour period, including the first morning urine on the second day. (5) Return the container to the lab as instructed. It's important to collect every urine sample during the 24-hour period for accurate results.
Reference range
2.0-9.0 mg/24 hours (typical adult reference range; may vary by laboratory)N/A
Avoid serotonin-rich foods (bananas, pineapples, walnuts, avocados, tomatoes, eggplant, chocolate) for 24-48 hours before and during collection. Avoid medications that may interfere including antidepressants, antipsychotics, monoamine oxidase inhibitors, and cough suppressants. Inform physician of all current medications.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Elevated 5-HIAA levels in urine typically indicate a carcinoid tumor, most commonly found in the gastrointestinal tract or lungs. These tumors are part of a group of cancers called neuroendocrine tumors. High levels help confirm the diagnosis and also guide treatment decisions. The test is also valuable for monitoring disease progression or recurrence. Low or normal 5-HIAA levels generally indicate no evidence of serotonin-producing tumors, though your doctor may order additional tests if symptoms persist.
Frequently asked questions
Do I need to fast before the test?
Should I stop taking my medications?
Can I drink water during the collection?
When will I get my results?
What do abnormal results mean?
Sources
- 1MedlinePlus - 5-HIAASource
- 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 16, 2026. · Read our editorial policy