5-HIAA
Pronunciation: five-H-I-double-A
The major urinary metabolite of serotonin used as a biomarker for carcinoid tumors and syndrome.
Full Definition
5-Hydroxyindoleacetic acid (5-HIAA) is the primary metabolite of serotonin produced through enzymatic degradation by monoamine oxidase and aldehyde dehydrogenase. Measurement of 24-hour urinary 5-HIAA excretion serves as the gold standard biochemical test for diagnosing carcinoid syndrome and monitoring treatment response in patients with serotonin-secreting neuroendocrine tumors. Elevated levels correlate with tumor burden and disease activity. False elevations can occur with certain foods (bananas, avocados, nuts) and medications, requiring dietary restrictions before collection. Normal values are typically less than 6 mg per 24 hours, with significant elevations suggesting active carcinoid syndrome.
Usage
Usage note: Always specify 24-hour urine collection; random samples are unreliable.
In Context
- "The 24-hour urinary 5-HIAA level was markedly elevated at 45 mg, confirming active carcinoid syndrome." — Laboratory report
- "Serial 5-HIAA measurements showed a 70% reduction following initiation of octreotide therapy." — Treatment monitoring note