Carcinoid tumour marker tests - 5-hydroxyindoleacetic acid urine

Role

24-hour urinary 5-hydroxyindoleacetic acid (5-HIAA), the major serotonin breakdown product, is the standard biochemical test for suspected carcinoid syndrome - elevated in the setting of a serotonin-secreting neuroendocrine tumour with sufficient tumour burden or hepatic metastases to overwhelm hepatic serotonin clearance
Used specifically in patients presenting with the clinical carcinoid syndrome triad (flushing, diarrhoea, and in advanced disease, right-sided cardiac valve disease) rather than as a routine screen for asymptomatic neuroendocrine tumours

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