Complete Blood Count (CBC)
This test measures the level of 5-hydroxyindoleacetate (5-HIAA), a breakdown product of serotonin, in your blood to help diagnose and monitor certain neuroendocrine tumors.
{"5-HIAA is a substance produced when your body breaks down serotonin","This test mainly helps diagnose and monitor carcinoid tumors","A 24-hour urine collection is also commonly used alongside this blood test","Certain foods and medications can affect test results","Results help your doctor evaluate treatment effectiveness"}
Key facts at a glance
- LOINC
- 1693-1
- Short code
- 5-HIAA
- Synonyms
- 5OH-indoleacetate SerPl-mCnc
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or plain red top tube
- Units
- N/A
- Ref low
- 2
- Ref high
- 10
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 18 years
- Method
- High Performance Liquid Chromatography (HPLC) with electrochemical or fluorescence detection, or Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
- CPT
- 82157
- SNOMED
- 314180006
- Specimen volume
- 2-5 mL of serum
- Stability
- Room temperature: 24 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 30 days. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 50
- Lipemia max
- 100
- Icterus max
- 20
- TAT
- 24–72 hours
- Order
- routine
What is a complete blood count (CBC) test and what does it measure?
The 5-HIAA test measures the amount of 5-hydroxyindoleacetate in your serum or plasma. 5-HIAA is the main breakdown product (metabolite) of serotonin, a hormone and neurotransmitter that helps regulate mood, sleep, and other bodily functions. When your body processes serotonin, it produces 5-HIAA, which can be measured in blood and urine.
Why might my healthcare provider order a complete blood count (CBC)?
This test is primarily ordered to help diagnose and monitor carcinoid tumors, which are rare neuroendocrine tumors that often develop in the digestive tract or lungs. These tumors can produce excess serotonin, leading to elevated 5-HIAA levels. The test may also be used to evaluate symptoms like flushing, diarrhea, and abdominal pain that might suggest a carcinoid tumor.
The test is performed with a simple blood draw. A healthcare professional will clean the skin on your arm, wrap a band around your upper arm, and collect a small sample of blood from a vein, usually in the bend of your elbow. The sample is sent to a laboratory for analysis, and the entire procedure typically takes only a few minutes.
A healthcare professional will draw a blood sample from a vein in your arm. The blood is then sent to a laboratory for analysis. Your doctor may also ask you to collect urine over a 24-hour period, as 5-HIAA is excreted in urine. For the blood test, you may need to fast (not eat) for several hours before the sample is taken.
Preparing for a CBC is simple and usually requires no special steps. You can normally eat and drink before the test unless your provider asks you to fast because other blood tests are being done at the same time. Tell your provider about all medications and supplements you take, wear a short-sleeved shirt or loose clothing so your arm is easy to access, and drink plenty of water beforehand, which can make your veins easier to find.
Before the test, inform your doctor about all medications, vitamins, and supplements you are taking. Certain foods (like bananas, avocados, walnuts, and certain cheeses) and medications (including some antidepressants, cough medicines, and pain relievers) can affect serotonin and 5-HIAA levels. Your doctor may ask you to avoid these for 24-48 hours before the test.
Reference range
Reference range: 2.0-10.0 ng/mL (laboratory-specific). Values may vary by methodology and reference population.N/A
Patient should fast for 8-12 hours overnight. Avoid serotonin-rich foods for 24-48 hours before collection including bananas, avocados, walnuts, pecans, pineapples, tomatoes, kiwi, plums, and chocolate. Avoid medications that may interfere including MAO inhibitors, tricyclic antidepressants, levodopa, and acetaminophen. Inform physician of all current medications.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Elevated 5-HIAA levels may indicate carcinoid tumors, particularly those in the gastrointestinal tract. The test helps in diagnosing these tumors, determining the extent of the disease, and monitoring response to treatment. Normal or low levels do not rule out all tumors, as some may not produce excess serotonin. Your doctor will interpret results alongside your symptoms, imaging studies, and other laboratory tests.
Frequently asked questions
Does the test require fasting?
How long does it take to get results?
Are there any risks with this test?
Will I need both blood and urine tests?
What happens if my results are abnormal?
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