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5-Hydroxyindoleacetic Acid (5-HIAA) Urine


Definition


  • 5-Hydroxyindoleacetic acid (5-HIAA), also known as serotonin metabolite, is the major urinary metabolite of serotonin.
  • Normal range: 0.0 " “15.0 mg/day (24-hour urine); 0.0 " “14.0 mg/g creatinine.

Use


  • Helps diagnose and monitor treatment for serotonin-secreting carcinoid tumors

Interpretation


Increased In


  • Whipple disease
  • Nontropical sprue
  • Small increases possible in pregnancy, ovulation, and postsurgical stress
  • Various food ingestions (e.g., pineapples, kiwi, bananas, eggplant, plums, tomatoes, avocados, plantains, walnuts, pecans, hickory nuts, coffee)
  • Use of certain drugs (e.g., acetanilid, acetaminophen, acetophenetidin, caffeine, coumaric acid, diazepam [Valium], ephedrine, fluorouracil, glyceryl guaiacolate [guaifenesin], heparin, melphalan [Alkeran], mephenesin, methamphetamine, methocarbamol, naproxen, nicotine, Lugol solution, promethazine, phenothiazine, hydroxyl tryptophan)

Decreased In


  • Use of certain drugs (e.g., chlorpromazine, promazine, imipramine, isoniazid, monoamine oxidase inhibitors, methenamine, methyldopa, phenothiazines, promethazine)
  • Renal insufficiency (possible)

Limitations


  • Foods rich in serotonin and medications, over-the-counter drugs, and herbal remedies that may affect metabolism of serotonin must be avoided at least 72 hours before and during collection of urine for 5-HIAA.
  • Twenty-four " “hour collections are generally recommended, but random collections may be used. Refrigeration is the most important aspect of specimen preservation.
  • Urinary 5-HIAA is increased with malabsorption, in 75% of cases, usually when a carcinoid tumor is far advanced (with large liver metastases, often 300 " “1,000 mg/day), but may not be increased despite massive metastases.
  • Sensitivity is 73%.
  • The test is useful in the diagnosis of only 5 " “7% of patients with carcinoid tumors but in approximately 45% of those with liver metastases.
  • Disease extent and prognosis correlate generally with urine 5-HIAA excretion, and the level becomes normal after successful surgery. If urine HIAA is normal, the blood level of serotonin or a precursor, 5-hydroxytryptophan should be checked.
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