II. Indications

  1. Carcinoid Syndrome Evaluation

III. Mechanism

  1. Serotonin (5-Hydroxytryptamine) produced by Carcinoid
  2. Serotonin converted to 5-HIAA for excretion

IV. Interpretation

  1. Normal: Urine 5-HIAA < 9 mg/day
  2. Equivocal: Urine 5-HIAA 9 to 25 mg/day
    1. Possibly consistent with Carcinoid Syndrome
    2. See Other causes of 5-HIAA elevation
  3. High: Urine 5-HIAA >25 mg/day
    1. Diagnostic for Carcinoid Syndrome

V. Increased Urine 5-HIAA 24 hour Levels

  1. Malignant Carcinoid (>25 mg/day)
  2. Acute Intestinal Obstruction
  3. Celiac Sprue
  4. Excessive Banana or walnut ingestion

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