Hydroxyindole Acetic Acid

Serotonin is a neurotransmitter hormone in the human brain. It plays a significant role in transferring nerve impulses from the brain and also enables the narrowing of blood vessels.   Tryptophan is the amino acid responsible for producing serotonin. 

The 5-Hydroxyindole Acetic Acid (5-HIAA) is the chief product of serotonin’s metabolism.  The alternate name for this substance is ‘Serotonin Metabolite’. Urine tests can help ascertain the amount of 5-HIAA in order to determine the serotonin levels.


To measure the serotonin levels accurately it is important to maintain the pH levels. This is done by adding an acidic substance to the sample. Certain health issues can also prevent an accurate reading of 5-HIAA like bowel resection, presence of tumor or problems in kidneys. The normal range for this test is 3 to 15 milligrams in urine collected for 24 hours.

The 5-HIAA tests are performed to detect

  •   Malignant tumor in the enterochromaffin cells of intestine: When this tumor occurs, the small intestine will release large amounts of serotonin. Presence of more than 25 mg of 5-HIAA in one day provides a significant clue to the presence of the cancerous tumor
  •  Elevated serotonin levels may also indicate the possibility of autism
  •   A nervous disorder, or neurological imbalance is detected if the 5-HIAA levels are high and the (1) vanillaymandelic acid and/or (2) homovanillic acid levels are low

a.  Vanillaymandelic acid is a significant metabolite of catecholamine, a substance produced in the medulla of the adrenal gland

b.      Homovanillic acid is an important metabolite of dopamine

  • If the 5-HIAA levels are lower than normal in the cerebrospinal fluid it indicates the root cause for violent behavior and suicidal tendencies


How the sample is taken For 5-HIAA test

Urine collected over the whole day is needed for the 5-HIAA test.

  • On the first day collect all the urine except the first in the morning
  • On the second day collect the first urine and cap the bottle. 
  • Keep the container in a cool place until submitted for test
  • Before submitting for test attach a label with the date, time of completion of the test and your name
  • Use a urine collection bag to collect urine of infants and take care to see that the sample is corrected properly, as infants may jerk or shake while sample is being taken

Precautions before test

The health care provider will advise you about the efficacy of continuing or discontinuing certain medications that may interfere with the correct 5-HIAA level readings

  • Certain cough syrups may contain substances that will elevate 5-HIAA levels
  • Certain anti-depressants may reduce 5-HIAA levels
  • Walnuts, avocados, vegetables like tomatoes and eggplants and fruits like bananas and pineapples can disturb normal 5-HIAA levels and your doctor may ask you to avoid these for three days prior to the test

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