Test Directory

A serotonin analysis is most frequently performed for the diagnosis of carcinoid tumors of the enterochromaffin (Kultschitzsky) cells of the small intestine. These tumor cells release large amounts of serotonin, which can produce the clinical syndrome of flushing, diarrhea, and right-sided heart failure. The most frequently used diagnostic test for carcinoid tumors is 5-HIAA, the final metabolite of serotonin. Diagnose carcinoid tumors and syndrome; values >25 mg/24 hours (higher if the patient has malabsorption) are strong evidence for carcinoid.

Specimen Type: Random Urine

Collection Container: Plastic Urine Container (Preservative Free)   

Desired Specimen Volume: 1 mL

1. Collect random urine in a plastic urine container (preservative free).

1. Transfer 1 mL of random urine to a clear aliquot tube (screw cap).

Avoid bananas, avocados, plums, eggplant, tomatoes, plantain, pineapple, walnuts, and interfering drugs for a 72 hour period prior to and during collection. Foods and medications associated with altered urinary HIAA results: Decreased HIAA: Aspirin, chlorpromazine (Thorazine), corticotropin, dihydroxyphenylacetic acid, alcohol, gentisic acid, homogentisic acid, hydrazine derivatives, imipramine (Tofranil®), <isocarboxazid (Marplan), keto acids, levodopa, MAO inhibitors, methenamine methyldopa (Aldomet®), perchlorperazine, phenothiazines (Compazine®), promazine, promethazine (Mepergan®). Increased HIAA: Acetaminophen, acetanilide, caffeine, coumaric acid, diazepam (Valium®), ephedrine, fluorouracil glycerol guaiacolate (Guaifenesin), melphalan (Alkeran®), mephenesin, methamphetamine (Desoxyn), methocarbamol (Robaxin®), naproxen, nicotine, phenacetin, phenmetrazine, phenobarbital, phentolamine, rauwolfia, reserpine.

Transport to the laboratory refrigerated. 

• pH <2

See patient report.

5-HIAA may be normal with nonmetastatic carcinoid tumor and may be normal even with the carcinoid syndrome, particularly in subjects without diarrhea. Some patients with the carcinoid syndrome excrete nonhydroxylated indolic acids, not measured as 5-HIAA. Midgut carcinoids are most apt to produce the carcinoid syndrome with 5-HIAA elevation. Patients with renal disease may have falsely low 5-HIAA levels in the urine. 5-HIAA is increased in untreated patients with malabsorption, who have increased urinary tryptophan metabolites. Such patients include those with celiac disease, tropical sprue, Whipple disease, stasis syndrome, and cystic fibrosis. It is increased in those with chronic intestinal obstruction. Poor correlation exists between 5-HIAA level and the clinical severity of the carcinoid syndrome. Recent studies confirm its use as a prognostic factor in this disease.

• 5-HIAA, Quantitative, Random Urine
• Serotonin Metabolite, Random Urine