Question:
HIAA (5-hydroxyindoleacetic acid) is present in the urine in which condition?
HIAA (5-hydroxyindoleacetic acid) is present in the urine in which condition?
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5-HIAA is a serotonin metabolite - which serotonin-secreting tumour raises it?
Updated On: Jun 23, 2026
- Alkaptonuria
- Albinism
- Carcinoid
- Phenylketonuria
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The Correct Option is C
Solution and Explanation
Step 1: 5-hydroxyindoleacetic acid (5-HIAA) is the major urinary breakdown product of serotonin (5-hydroxytryptamine).
Step 2: Carcinoid tumours, usually arising in the appendix, ileum or rectum, secrete serotonin and other vasoactive substances. Carcinoid syndrome then presents with cutaneous flushing, abdominal cramps, diarrhoea, and right-sided valvular heart disease over time.
Step 3: Because the tumour overproduces serotonin, urinary 5-HIAA is markedly raised and forms the diagnostic test. Hence the answer is Carcinoid.
Step 4: The distractors involve unrelated pathways: alkaptonuria gives urinary homogentisic acid, albinism is a defect of melanin synthesis with no urinary marker, and phenylketonuria gives urinary phenylketones - none raise 5-HIAA.
Step 2: Carcinoid tumours, usually arising in the appendix, ileum or rectum, secrete serotonin and other vasoactive substances. Carcinoid syndrome then presents with cutaneous flushing, abdominal cramps, diarrhoea, and right-sided valvular heart disease over time.
Step 3: Because the tumour overproduces serotonin, urinary 5-HIAA is markedly raised and forms the diagnostic test. Hence the answer is Carcinoid.
Step 4: The distractors involve unrelated pathways: alkaptonuria gives urinary homogentisic acid, albinism is a defect of melanin synthesis with no urinary marker, and phenylketonuria gives urinary phenylketones - none raise 5-HIAA.
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