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Introduction ⬇

Serotonin is a vasoconstricting hormone normally produced by the argentaffin cells of the gastrointestinal tract. The principal function of the cells is to regulate smooth muscle contraction and peristalsis. 5-Hydroxyindoleacetic acid (5-HIAA) is the major urinary metabolite of serotonin. 5-HIAA assays are more useful than the parent hormone serotonin.

This urine test is conducted to diagnose the presence of a functioning carcinoid tumor, which can be shown by significant elevations of 5-HIAA. Excess amounts of 5-HIAA are produced by most carcinoid tumors. Carcinoid tumors produce symptoms of flushing, hepatomegaly, diarrhea, bronchospasm, and heart disease.

Normal Findings ⬆ ⬇

Qualitative: negative

Quantitative: 2–7 mg/24 hr or 10.4–36.4 μmol/d

Procedure ⬆ ⬇

  1. Tell the patient to not eat any bananas, pineapple, tomatoes, eggplants, plums, or avocados for 48 hours before or during the 24-hour test because these foods contain serotonin.

  2. Properly label (patient’s name, date and time of collection, and test ordered) a 24-hour urine container that contains a preservative.

  3. Discontinue the following drugs 48 hours before sample collection with healthcare provider approval: acetaminophen, salicylates, phenacetin, naproxen, imipramine, and monoamine oxidase inhibitors.

  4. Follow general directions for 24-hour urine collection (see Long-Term, Timed Urine Specimen [2-Hour, 24-Hour]).

  5. Record exact starting and ending times of the collection on the specimen container and in the patient’s healthcare record.

  6. Send the completed specimen to the laboratory.

Clinical Implications ⬆ ⬇

  1. Levels >25 mg/24 hr or >130 μmol/d indicate large carcinoid tumors, especially when metastatic:

    1. Ileal tumors

    2. Pancreatic tumors

    3. Duodenal tumors

    4. Biliary tumors

  2. Increased urine 5-HIAA is found in:

    1. Ovarian carcinoid tumor

    2. Nontropical sprue

    3. Bronchial adenoma (carcinoid type)

    4. Malabsorption

    5. Celiac disease

    6. Whipple disease

    7. Oat cell cancer of the respiratory system

  3. Decreased urine 5-HIAA is found in:

    1. Depressive illness

    2. Small intestine resection

    3. PKU

    4. Hartnup disease

    5. Mastocytosis

Clinical Alert

A serum serotonin assay may detect some carcinoids missed by the urine 5-HIAA assay

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain purpose of test, procedure for 24-hour urine collection, and interfering factors. Written instructions can be helpful.

  2. Encourage food and fluids. Foods high in serotonin content must not be eaten for 48 hours before or during the test.

  3. Obtain healthcare provider’s approval to discontinue medications for 72 hours before or during specimen collection, if possible, especially aforementioned drugs and including over-the-counter drugs.

  4. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Have the patient resume a normal diet and medications.

  2. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel patient regarding abnormal findings.

  3. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Interfering Factors ⬆

  1. False-positive results occur with:

    1. Ingestion of banana, pineapple, plum, tomato, eggplant, chocolate, walnuts, and avocado because of their serotonin content

    2. Many drugs (see Appendix E)

    3. After surgery (surgical stress)

  2. False-negative results can be caused by specific drugs that depress 5-HIAA production.