Understanding 5-HIAA: Normal vs Optimal Ranges

?What is 5-HIAA?

5-Hydroxyindoleacetic acid (5-HIAA) is the primary urinary metabolite of serotonin (5-hydroxytryptamine). Serotonin produced in enterochromaffin cells of the gut is metabolised by MAO to 5-HIAA, which is excreted in urine. It is measured in a 24-hour or spot urine sample to assess serotonin production and turnover.

!Why It Matters

Markedly elevated urinary 5-HIAA is the key diagnostic biomarker for carcinoid tumours (well-differentiated neuroendocrine tumours, usually in the gut), which secrete excess serotonin. Carcinoid syndrome — flushing, diarrhoea, bronchospasm, and valvular heart disease — results from systemic serotonin excess. 5-HIAA is also used in research on serotonin metabolism in depression, anxiety, and autism spectrum disorder.

Reference Ranges

Lab normal ranges may vary between laboratories. Optimal and longevity targets are based on research literature and should be interpreted with your physician.

Symptoms of Imbalance

• Carcinoid syndrome: flushing, watery diarrhoea, bronchospasm, carcinoid heart disease
• Low 5-HIAA associated with depression, aggressive behaviour in some studies

How to Improve Your Levels

• 1Carcinoid tumour: surgical resection; somatostatin analogues (octreotide) to reduce serotonin secretion
• 2Avoid 5-HIAA-raising foods before testing: avocado, banana, pineapple, tomato, walnuts
• 3Serotonin support: adequate tryptophan (5-HTP precursor), vitamin B6 as cofactor

When to Test

Suspected carcinoid/neuroendocrine tumour; flushing and diarrhoea workup; serotonin metabolism research.

Related Biomarkers