5-Hydroxy Indole Acetic Acid (5-HIAA)

The 5‑HIAA test measures the serotonin breakdown product in a 24‑hour urine sample to help diagnose and monitor serotonin‑producing neuroendocrine (carcinoid) tumors. It’s used when patients have flushing, diarrhea, wheezing or suspected carcinoid syndrome, and to assess treatment response or recurrence. Preparations may include dietary and medication restrictions to avoid false results.

5‑Hydroxyindoleacetic acid (5‑HIAA) is the main urinary breakdown product of serotonin. Its purpose is to assess serotonin production and to help diagnose and monitor serotonin‑secreting neuroendocrine (carcinoid) tumors. Elevated urinary 5‑HIAA supports a carcinoid diagnosis, aids evaluation of symptoms such as flushing and diarrhea, and is used to track treatment response or detect tumor recurrence.

Normal 5‑HIAA in a 24‑hour urine collection is usually about 2–8 mg per 24 hours (many labs use <10 mg/24 h as the upper limit). Reference ranges and units vary between laboratories; results can be affected by diet, alcohol, and certain medications, so abnormal values should be interpreted with clinical context and follow‑up testing.

Yes. Foods high in serotonin or tryptophan (bananas, pineapple, kiwi, tomatoes, walnuts, avocado, chocolate and others) can raise urinary 5‑HIAA, so these are usually avoided 24–72 hours before a 24‑hour urine test. Certain medications and supplements also affect results. Follow your lab’s pretest instructions and tell your clinician about all foods, drugs, and supplements you take.

Elevated urinary 5‑hydroxyindoleacetic acid (5‑HIAA) is most commonly associated with serotonin‑secreting neuroendocrine (carcinoid) tumors, especially midgut carcinoids, and supports diagnosis of carcinoid syndrome (flushing, diarrhea, wheeze). Levels are interpreted alongside symptoms and imaging; false positives or negatives can occur due to diet, medications, or other conditions, so clinical correlation is needed.

Carcinoid tumors are neuroendocrine neoplasms arising from enterochromaffin (neuroendocrine) cells in the gastrointestinal tract and lungs. Their precise cause is unknown; most occur sporadically. Known risk factors include inherited syndromes (e.g., MEN1, neurofibromatosis type 1), family history, advancing age, and some chronic gastrointestinal conditions. Tumor behavior depends on location and genetic changes.