5-HIAA Urine Test – Indications, Procedures, Results

Last updated: February 8, 2026 Medically reviewed by: RxHarun Orthopedic Specialist Doctor Reading time: 5 min read

HIAA; 5-hydroxy indole acetic acid; Serotonin metabolite

5-Hydroxyindoleacetic acid (5-HIAA) is the main metabolite of serotonin. In the chemical analysis of urine samples, 5-HIAA is used to determine serotonin levels in the body.5-HIAA is a urine test that measures the amount of 5-hydroxy indole acetic acid (5-HIAA). 5-HIAA is a breakdown product of a hormone called serotonin.

5-HIAA is a urine test that measures the amount of 5-hydroxyindoleacetic acid (5-HIAA). 5-HIAA is a breakdown product of a hormone called serotonin. This test tells how much 5-HIAA the body is producing. It is also a way to measure how much serotonin is in the body.

This test tells how much 5-HIAA the body is producing. It is also a way to measure how much serotonin is in the body. 5-HIAA is tested by 24-hour urine samples combined with an acidic additive to maintain pH below 3. Certain foods and drugs are known to interfere with the measurement. 5-HIAA levels can vary depending on other complications, including tumors, renal malfunction, and small bowel resection.

Since 5-HIAA is a metabolite of serotonin, testing is most frequently performed for the diagnosis of carcinoid tumors of the enterochromaffin (Kultschitzsky) cells of the small intestine, which release large amounts of serotonin. Values greater than 25 mg per 24 hours (higher if the patient has malabsorption) are strong evidence of carcinoid. The normal range is 2 to 6 mg per 24 hours.^[rx]

Low levels of 5-HIAA in the cerebrospinal fluid have been associated with aggressive behavior and suicide by violent means, correlating with diminished serotonin levels.^[rx]

Elevated serotonin (hyperserotonemia) is one of the most common biological findings in autism^[rx] and 5-HIAA may be elevated in patients with autistic spectrum disorders.

How the Test is Performed

A 24-hour urine sample is needed. You’ll need to collect your urine over 24 hours in a container provided by the laboratory. Your health care provider will tell you how to do this. Follow instructions exactly.

How to Prepare for the Test

Your provider will instruct you, if necessary, to stop taking medicines that may interfere with the test.

Medicines that can increase 5-HIAA measurements include acetaminophen (Tylenol), acetanilide, phenacetin, glyceryl guaiacolate (found in many cough syrups), methocarbamol, and reserpine.

Medicines that can decrease 5-HIAA measurements include heparin, isoniazid, levodopa, monoamine oxidase inhibitors, methenamine, methyldopa, phenothiazines, and tricyclic antidepressants.

You will be told not to eat certain foods for 3 days before the test. Foods that can interfere with 5-HIAA measurements include plums, pineapples, bananas, eggplant, tomatoes, avocados, and walnuts.

How the Test will Feel

The test involves only normal urination, and there is no discomfort.

Why the Test is Performed

This test measures the level of 5-HIAA in the urine. It is often done to detect certain tumors in the digestive tract ( carcinoid tumors ) and to track a person’s condition.

The urine test may also be used to diagnose a disorder called systemic mastocytosis and some tumors of the hormone.

Normal Results

The normal range is 2 to 9 mg/24h (10.4 to 46.8 Âµmol/24h).

Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

What Abnormal Results Mean

Abnormal results may be due to:

Tumors of the endocrine system or carcinoid tumors
Systemic mastocytosis

Risks

There are no risks with this test.

FAQ

What does high Hydroxyindoleacetic acid mean?

Higher levels of 5-HIAA may mean you have: Carcinoid tumors. Noncarcinoid tumors. Cystic fibrosis.

What does a high level of 5-HIAA mean?

24-hour urine 5-HIAA test
With elevated values, levels greater than 25 mg/24 h or greater than 131 µmol/day indicate large carcinoid tumors, especially when in ileal, biliary, pancreatic, or duodenal tumors.

What is a normal 5-HIAA level?

The normal range is 2 to 9 mg/24h (10.4 to 46.8 µmol/24h). Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.

What can cause elevated 5-HIAA?

Medications that can increase 5-HIAA include acetaminophen, caffeine, ephedrine, diazepam (Valium®), fluorouracil, glyceryl guaiacolate (an ingredient found in some cough medicines), melphalan (Alkeran®), mephenesin, methamphetamine (Desoxyn), methocarbamol (Robaxin®), naproxen, nicotine, phenacetin, phenmetrazine

What does the 5-HIAA urine test for?

5-HIAA is a urine test that measures the amount of 5-hydroxyindoleacetic acid (5-HIAA). 5-HIAA is a breakdown product of a hormone called serotonin. This test tells how much 5-HIAA the body is producing. It is also a way to measure how much serotonin is in the body.

How accurate is the 5-HIAA urine test?

Urine 5-HIAA has been shown to have a sensitivity of 73% and specificity of 100% for diagnosing well-differentiated functional gastroenterohepatic neuroendocrine tumors.

What could cause a false positive result in a urine 5-HIAA test?

False-positive 24-hour urine 5-HIAA results may be induced by the ingestion of tryptophan/serotonin-rich foods (pineapple, banana, kiwi, plum, tomato, avocado, walnut, eggplant, hickory nut, etc.), and certain medications and supplements such as acetaminophen, nicotine, and caffeine (5,6).

What disease may be associated with decreased 5-HIAA levels?

For instance, we know that a patient with depression shows a significant reduction in the levels of 5HIAA, due to the location of the raphe nuclei within regions of memory and cognition. Similarly, it does show variation in AD and mild cognitive disorder.

What does a low 5-HIAA mean?

In patients treated for a carcinoid tumor, decreasing levels of 5-HIAA indicate a response to treatment, while increasing or excessive levels indicate a non-response.

Does alcohol affect the 5-HIAA test?

Tea, coffee, and nicotine can elevate 5HIAA results. Alcohol can cause falsely lower 5HIAA results

Frequently Asked Questions

Is this article a replacement for a doctor?

No. It is educational content only. Patients should consult a qualified clinician for diagnosis and treatment.

When should I seek urgent care?

Seek urgent care for severe symptoms, rapidly worsening condition, breathing difficulty, severe pain, neurological changes, or any emergency warning sign.

References

Add references, clinical guidelines, textbooks, journal articles, or trusted medical sources here. You can edit this area later with a custom field named _rx_references.

Written by Dr. Harun Ar Rashid, MD - Arthritis, Bones, Joints Pain, Trauma, and Internal Medicine Specialist

Dr. Md. Harun Ar Rashid, MPH, MD, PhD, is a highly respected medical specialist celebrated for his exceptional clinical expertise and unwavering commitment to patient care. With advanced qualifications including MPH, MD, and PhD, he integrates cutting-edge research with a compassionate approach to medicine, ensuring that every patient receives personalized and effective treatment. His extensive training and hands-on experience enable him to diagnose complex conditions accurately and develop innovative treatment strategies tailored to individual needs. In addition to his clinical practice, Dr. Harun Ar Rashid is dedicated to medical education and research, writing and inventory creative thinking, innovative idea, critical care managementing make in his community to outreach, often participating in initiatives that promote health awareness and advance medical knowledge. His career is a testament to the high standards represented by his credentials, and he continues to contribute significantly to his field, driving improvements in both patient outcomes and healthcare practices. Born and educated in Bangladesh, Dr. Rashid earned his BPT from the University of Dhaka before pursuing postgraduate training internationally. He completed his MD in Internal Medicine at King’s College London, where he developed a special interest in inflammatory arthritis and metabolic bone disease. He then undertook a PhD in Orthopedic Science at the University of Oxford, conducting pioneering research on cytokine signaling pathways in rheumatoid arthritis. Following his doctoral studies, Dr. Rashid returned to clinical work with a fellowship in interventional pain management at the Rx University School of Medicine, refining his skills in image-guided joint injections and minimally invasive pain-relief techniques.