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5-Hydroxyindoleacetic acid (5-HIAA) is the major metabolite of serotonin and is excreted in the urine. Intestinal carcinoid tumors along with neuroendocrine tumors can produce excess amounts of 5-HIAA and serotonin especially in individuals with carcinoid syndrome. Carcinoid syndrome is characterized by carcinoid tumors, flushing, heart disease, and hepatomegaly.
Measurement of 5-HIAA in a 24-hour urine specimen can diagnose carcinoid disease with a high specificity.
Biochemical diagnosis and monitoring of intestinal carcinoid syndrome
Elevated excretion of 5-hydroxyindoleacetic acid is a probable indicator of the presence of a serotonin-producing tumor, if pharmacological and dietary artifacts have been ruled out.
Intake of food with a high content of serotonin (avocados, dates, eggplant, all fruit [including bananas, cantaloupe, grapefruit, kiwifruit, melons, pineapple, plantains, plums], all nuts [including hickory nuts, butternuts, pecans, walnuts], and tomatoes and tomato products) within 48 hours of the urine collection could result in falsely elevated 5-hydroxyindoleacetic acid (5-HIAA) excretion.
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. If clinically feasible, discontinue the following medications at least 48 hours before specimen collection.
-Pain relievers (specifically those containing acetaminophen [Tylenol], salicylates [aspirin] or phenacetin)
-Cough syrups containing guaifenesin or antihistamines
-Nasal drops and sprays
-Muscle relaxants containing mephenesin or methocarbamol (Robaxin, Flexeril, and Valium for example)
-Antidepressants including tricyclic antidepressants (imipramine, for example) and monamine oxidase inhibitors (MAOIs) (Nardil, for example)
-Hypertensive medications (Reserpine, for example)
-Isoniazid (antibiotic used to fight tuberculosis and other diseases)
-Methenamine (antibiotic used to fight urinary tract infections)
-Heparin (anticoagulant used as a blood thinner)
-L-dopa (Levodopa such as Sinemet, or Methyldopa, used to treat high blood pressure, for example)
-Phenothiazines (Compazine or Thorazine for example, used to treat mental or emotional disorders)
Patient should also avoid tobacco, tea and coffee for 48 hours before and during specimen collection.
< or =8 mg/24 hours
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