5-HIAA Lab Test

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The 5-HIAA lab test measures how much 5-hydroxyindoleacetic acid the body is producing. 5-HIAA is a break-down product of serotonin. This urine test is performed for a number of reasons and may be ordered in combination with a blood serotonin level.

How this Test is Used

This test, also sometimes referred to as a serotonin metabolite test, is done to help monitor and help to diagnose carcinoid tumors. In order to get the most accurate results, a 24-hour urine sample should be collected due to the urine’s metabolite level varying throughout the day. In some cases, a random urine sample is test, often in combination with a urine creatinine level, when a 24-hour sample cannot be taken. However, random samples are not as accurate.

What is this Test Used For and When is it Ordered?

This test is typically ordered when a patient is suspected to have a possible carcinoid tumor. Some symptoms of this type of tumor that may prompt this test be performed include:

  • Facial and neck flushing (typically has a sudden onset and is deep red in color)
  • Rapid heart rate
  • Diarrhea, vomiting, and nausea
  • Coughing, wheezing, and difficulty breathing

The 5-HIAA lab test can also be done to monitor how effective the treatment is for patients who have already been diagnosed and are already undergoing treatment for a serotonin-secreting carcinoid tumor.

This test may also be ordered when certain other types of tumors are suspected. When a doctor is seeking to diagnose endocrine tumors and systemic mastocytosis.

Preparation and Procedure

Preparation is necessary for this lab test. Certain drugs will decrease 5-HIAA and may have to be discontinued for a certain period of time prior to having this test. These include:

  • Chlorpromazine
  • Imipramine
  • Levodopa
  • Methenamine
  • Phenothiazines
  • Tricyclic antidepressants
  • Heparin
  • Isoniazid
  • Monoamine oxidase inhibitors
  • Methyldopa
  • Promethazine

Certain drugs will increase 5-HIAA and may have to be discontinued for a certain period of time prior to having this test. These include:

  • Acetanilid
  • Glyceryl guaiacolate
  • Reserpine
  • Phenacetin
  • Methocarbamol

Certain foods cannot be consumed three days prior to this test because they can interfere with the measurements of 5-HIAA. These foods include:

  • Plums
  • Bananas
  • Tomatoes
  • Walnuts
  • Pineapples
  • Eggplant
  • Avocados
  • Kiwi

Patients will begin the testing procedure in the morning by urinating in the toilet. They will then begin collecting all other urine throughout the next 24 hours in a special container. On the second day, they will urinate in the special container first thing in the morning. The container should be kept in a refrigerator during the collection period. The patient should take it to where their doctor instructs when he or she instructs them to do so. There is not discomfort associated with this test.

What do the Results Mean?

Normal results fall in the three to fifteen milligrams per 24 hours range. Abnormal results could indicate:

  • Mastocytosis
  • Digestive tract tumors (such as a carcinoid tumor)
  • Endocrine system tumors


Lab Tests Online. (2010). 5-HIAA. Retrieved on September 8, 2010 from Lab Tests Online: https://www.labtestsonline.org/understanding/analytes/5hiaa/test.html

MedlinePlus. (2008). 5-HIAA. Retrieved on September 8, 2010 from MedlinePlus: https://www.nlm.nih.gov/medlineplus/ency/article/003612.htm