5-hydroxyindolacetic acid (5-HIAA) is the major metabolite of serotonin in the urine. Under normal conditions, serotonin is produced in the gastrointestinal tract and acts as a vasoconstrictor substance. About 5% of serotonin is converted to 5-HIAA and excreted in the urine. Increased secretion of 5-HIAA is indicative of serotonin overproduction, as with carcinoid tumors.
What Do Pathological Values Mean?
- Increase: Carcinoid tumors, testicular tumors, celiac disease, diarrhea, endocarditis, ganglioneuroblastoma, preeclampsia, tropical diarrhea. Medications: acetaminophen (paracetamol), atenolol, cisplatin, diazepam, fluorouracil, melphalan, mephenezine, methocarbamol, naproxen, oxprenolol, phenacetin, pindolol, reserpine.
- Decrease: Carcinoid tumors (rectal), depression, Hartnup's disease, mastocytosis, non-metastatic carcinoid tumors, phenylketonuria, diarrhea due to small bowel resection, high serum triglyceride levels. Medications: corticotropin, dihydroxyphenylacetic acid, ethyl alcohol (ethanol), formaldehyde, gentisic acid, homogentisic acid, imipramine, isoniazid, lanreotide, levodopa, methenamine, methyldopa, monoamine oxidase (MAO) inhibitors, phenothiazines, salicylates, sulfasalazine.
Certain foods such as bananas, avocados, prunes, eggplants, tomatoes, pineapple, and walnuts can increase urine 5-HIAA levels. These foods should be avoided a few days before and during urine collection.
Important Note
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. The correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings, and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.
