Lab marker · High

High 5-HIAA (5-hydroxyindoleacetic acid): what it means

A 5-HIAA (5-hydroxyindoleacetic acid) result above the normal range is considered high. Here is what a raised 5-HIAA (5-hydroxyindoleacetic acid) can point to, and when it is worth discussing with a doctor.

Reference range: 24-hour urine ~2–8 mg/day; a high level suggests a serotonin-producing carcinoid tumour — but many foods and drugs must be avoided beforehand to avoid false results

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What a high 5-HIAA (5-hydroxyindoleacetic acid) can mean

  • Carcinoid tumour / carcinoid syndrome — the key use; excess serotonin from a neuroendocrine tumour.
  • Serotonin-rich foods eaten before the test — bananas, pineapple, avocado, walnuts, tomatoes; a common cause of a false high.
  • Certain medicines — some can raise it; a drug review is part of interpreting the result.
  • Malabsorption conditions (e.g. coeliac disease) — occasionally raise it modestly.

When to discuss with a doctor

Urinary 5-HIAA is a targeted specialist test, ordered mainly when carcinoid syndrome is suspected — for example unexplained flushing with diarrhoea — or to monitor a known carcinoid tumour. Its accuracy depends heavily on preparation: the serotonin-rich foods and interfering medicines must be avoided as instructed for a few days before and during the 24-hour urine collection, or the result can be falsely high. A genuinely raised level, interpreted with chromogranin A and imaging, points toward a carcinoid tumour that needs specialist management. Mediora.AI can surface a raised 5-HIAA from your results and flag the carcinoid pattern for review, but confirming the diagnosis and its treatment is a specialist assessment — the interpretation belongs with your doctor.

Conditions this can relate to

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Mediora.AI is informational - interpretation, not a diagnosis. A single out-of-range value is common and often benign; always discuss decisions with your doctor.