5-hydroxyindoleacetic acid

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5-hydroxyindoleacetic acid

a product of serotonin metabolism excreted in large amounts in patients with carcinoid tumors. Abbreviated 5-HIAA.

5-hydroxyindoleacetic acid

/5-hy·droxy·in·dole·ace·tic ac·id/ (-in″dōl-ah-se´tik) a product of serotonin metabolism present in increased amounts in the urine in patients with carcinoid tumors.

5-hydroxyindoleacetic acid (5-HIAA)

an acid produced by serotonin metabolism, measured in the blood and urine to aid in the diagnosis of certain kinds of tumors. It commonly rises above normal levels in whole blood in association with asthma, diarrhea, rapid heartbeat, and other symptoms and is elevated in the urine of patients with carcinoid syndrome. Its normal concentration in whole blood is 0.05 to 0.20 g/mL; its normal accumulation in urine after 24-hour collection is 1 to 5 mg.

5-Hydroxyindoleacetic Acid

Synonym/acronym: 5-HIAA.

Common use

To assist in diagnosing carcinoid tumors.


Urine (10 mL) from a timed specimen collected in a clean plastic collection container with boric acid as a preservative.

Normal findings

(Method: High-pressure liquid chromatography)
Conventional UnitsSI Units (Conventional Units × 5.23)
2–7 mg/24 hr10.5–36.6 micromol/24 hr


Because 5-hydroxyindoleacetic acid (5-HIAA) is a metabolite of serotonin, 5-HIAA levels reflect plasma serotonin concentrations. 5-HIAA is excreted in the urine. Increased urinary excretion occurs in the presence of carcinoid tumors. This test, which replaces serotonin measurement, is most accurate when obtained from a 24-hr urine specimen.

This procedure is contraindicated for



  • Detect early, small, or intermittently secreting carcinoid tumors

Potential diagnosis

Increased in

  • Serotonin is produced by the enterochromaffin cells of the small intestine and secreted ectopically by tumor cells. It is converted to 5-HIAA in the liver and excreted in the urine. Increased values are associated with malabsorption conditions, but the relationship is unclear.

  • Celiac and tropical sprue
  • Cystic fibrosis
  • Foregut and midgut carcinoid tumors
  • Oat cell carcinoma of the bronchus
  • Ovarian carcinoid tumors
  • Whipple’s disease

Decreased in

    The documented relationship between decreased levels of serotonin, defective amino acid metabolism, and mental illness is not well understood.

    Depressive illnesses Hartnup’s disease Mastocytosis Phenylketonuria Renal disease (related to decreased renal excretion) Small intestine resection (related to a decrease in enterochromaffin-producing cells)

Critical findings


Interfering factors

  • Drugs that may increase 5-HIAA levels include cisplatin, fluorouracil, cough syrups containing glyceryl guaiacolate, melphalan, rauwolfia alkaloids, and reserpine.
  • Drugs that may decrease 5-HIAA levels include chlorophenylalanine, corticotropin, ethanol, imipramine, isocarboxazid, isoniazid, levodopa, methyldopa, monoamine oxidase inhibitors, and octreotide.
  • Foods containing serotonin, such as avocados, bananas, chocolate, eggplant, pineapples, plantains, red plums, tomatoes, and walnuts, can falsely elevate levels if ingested within 4 days of specimen collection.
  • Severe gastrointestinal disturbance or diarrhea can interfere with test results.
  • Failure to collect all the urine and store the specimen properly during the 24-hr test period invalidates the results.
  • Failure to follow dietary restrictions before the procedure may cause the procedure to be canceled or repeated.

Nursing Implications and Procedure


  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching:   Inform the patient this test can assist in diagnosing tumor.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s endocrine, gastrointestinal, and immune systems; symptoms; and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
  • Review the procedure with the patient. Provide a nonmetallic urinal, bedpan, or toilet-mounted collection device. Address concerns about pain and explain to the patient that there should be no discomfort during the procedure.
  • Inform the patient that all urine collected over a 24-hr period must be saved; if a preservative has been added to the container, instruct the patient not to discard the preservative. Instruct the patient not to void directly into the container. Instruct the patient to avoid defecating in the collection device and to keep toilet tissue out of the collection device to prevent contamination of the specimen. Place a sign in the bathroom as a reminder to save all urine.
  • Instruct the patient to void all urine into the collection device, then pour the urine into the laboratory collection container. Alternatively, the specimen can be left in the collection device for a health-care staff member to add to the laboratory collection container.
  • Sensitivity to social and cultural issues,  as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no fluid restrictions unless by medical direction.
  • Inform the patient that foods and medications listed under “Interfering Factors” should be restricted by medical direction for at least 4 days before specimen collection.


  • Potential complications: N/A
  • Ensure that the patient has complied with dietary and medication restrictions; assure foods and medications listed under “Interfering Factors” have been restricted for at least 4 days prior to the procedure.
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection.
  • Timed Specimen
  • Obtain a clean 3-L urine specimen container, toilet-mounted collection device, and plastic bag (for transport of the specimen container). The specimen must be refrigerated or kept on ice throughout the entire collection period. If an indwelling urinary catheter is in place, the drainage bag must be kept on ice.
  • Begin the test between 6 and 8 a.m. if possible. Collect first voiding and discard. Record the time the specimen was discarded as the beginning of the timed collection period. The next morning, ask the patient to void at the same time the collection was started, and add this last voiding to the container. Urinary output should be recorded throughout the collection time.
  • If an indwelling catheter is in place, replace the tubing and container system at the start of the collection time. Keep the container system on ice during the collection period, or empty the urine into a larger container periodically during the collection period; monitor to ensure continued drainage. Conclude the test the next morning at the same hour the collection was begun.
  • At the conclusion of the test, compare the quantity of urine with the urinary output record for the collection; if the specimen contains less than what was recorded as output, some urine may have been discarded, invalidating the test.
  • Include on the specimen collection container’s label the amount of urine, test start and stop times, and ingestion of any foods or medications that can affect test results. Promptly transport the specimen to the laboratory for processing and analysis.


  • Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
  • Instruct the patient to resume usual diet, as directed by the HCP.
  • Nutritional Considerations Consideration may be given to niacin supplementation and increased protein, if appropriate, for patients with abnormal findings. In some cases, the tumor may divert dietary tryptophan to serotonin, resulting in pellagra.
  • Recognize anxiety related to test results. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include ALP, amino acid screen, antibodies gliadin, biopsy intestine, biopsy lung, calcium, cancer antigens, capsule endoscopy, chloride sweat, fecal fat, and folate.
  • Refer to the Endocrine, Gastrointestinal, and Immune systems tables at the end of the book for related tests by body system.