What is 5-Hydroxyindoleacetate (5HIAA)?

What is 5HIAA?

5-Hydroxyindoleacetic acid (5HIAA) is a breakdown product of serotonin that is excreted in the urine. Serotonin is a hormone found at high levels in many body tissues. Serotonin and 5HIAA are produced in excess amounts by carcinoid tumors, and levels of these substances may be measured in the urine to test for carcinoid tumors.

5-Hydroxyindoleacetic acid is found to be associated with:

  • Aromatic l-amino acid decarboxylase deficiency an inherited disorder that affects the way signals are passed between certain cells in the nervous system.)
  • Celiac disease (an autoimmune disorder where the ingestion of gluten leads to damage in the small intestine)
  • Sepiapterin reductase deficiency (a condition characterized by movement problems)

What are normal levels?

Normal results are 3 to 15 milligrams (mg) of 5-HIAA over 24 hours. Women generally have lower levels than men.

What do higher levels mean?

High 5-HIAA can be caused by SSRI medication, 5-HTP supplementation, increased release of serotonin from the central nervous system, digestive system or platelets. Very high 5-HIAA levels can ironically indicated a tryptophan deficiency, as this may cause an increased conversion of tryptophan to serotonin.

Higher levels of 5-HIAA may mean you have:

  • Carcinoid tumors
  • Noncarcinoid tumors
  • Cystic fibrosis
  • Malabsorption

Increased urine 5-HIAA concentration is common and may be the result of improper specimen collection, consumption of serotonin containing foods or dietary supplements, drug interference, or malabsorption syndromes. Significant elevation (ten times the upper reference limit) of urine 5-HIAA may indicate the presence of a carcinoid tumor.

What do lower levels mean?

Low 5-HIAA indicates inadequate production of serotonin. Symptoms include: constipation, depression, fatigue, insomnia, attention deficit and behavioral disorders.

Lower levels of 5-HIAA may mean you have:

  • Depression
  • Migraines

What might affect the test results?

Eating certain foods containing serotonin can raise 5-HIAA levels. These foods include:

  • Cheese
  • Bananas
  • Pineapple
  • Kiwi
  • Plums
  • Tomatoes
  • Eggplant
  • Avocados
  • Certain nuts, including walnuts and pecans

Numerous drugs affect the excretion of 5-HIAA by different mechanisms, including increased serotonin synthesis, metabolism, and release and inhibition of uptake. The following medications can interfere with 5-HIAA results. Proper preparation before the test is essential. Medication and dietary restrictions are required to prevent false-positive results. If clinically feasible, discontinue the following medications at least 48 hours before specimen collection. 

  • Acetaminophen (Tylenol or generic versions)
  • Aspirin
  • Antihistamines
  • Cough syrups
  • Cold and flu medications

One should also avoid caffeinated beverages such as tea and coffee or caffeinated foods for 48 hours before and during specimen collection.

Certain medicines can raise or lower your 5-HIAA levels. These include:

  • Aspirin
  • Acetaminophen
  • Ethyl alcohol
  • Some antidepressants
  • Cough medicines or antihistamines
  • Medicines to relax muscles

Strenuous exercise can also raise your 5-HIAA levels.

Foods and medications associated with altered urinary HIAA results:

Decreased HIAA:

  • Aspirin,
  • chlorpromazine (Thorazine)
  • corticotropin
  • dihydroxyphenylacetic acid
  • alcohol
  • gentisic acid
  • homogentisic acid
  • hydrazine derivatives
  • imipramine (Tofranil®)
  • isocarboxazid (Marplan)
  • keto acids
  • levodopa
  • MAO inhibitors
  • methenamine
  • methyldopa (Aldomet®)
  • perchlorperazine
  • phenothiazines (Compazine®)
  • promazine
  • promethazine (Mepergan®)

Increased HIAA:

  • Acetaminophen
  • acetanilide
  • caffeine
  • coumaric acid
  • diazepam (Valium®)
  • ephedrine
  • fluorouracil
  • glycerol guaiacolate (Guaifenesin)
  • melphalan (Alkeran®)
  • mephenesin
  • methamphetamine (Desoxyn)
  • methocarbamol (Robaxin®)
  • naproxen
  • nicotine
  • phenacetin
  • phenmetrazine
  • phenobarbital
  • phentolamine
  • rauwolfia
  • reserpine



The information on is NOT intended to replace a one-on-one relationship with a qualified health care professional and is not intended as medical advice.


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