A patient presents with wheezing, severe diarrhea, and bright red facial flushing. Which initial test should be ordered?

• A. 5-HIAA urine level
• B. Abdominal CT
• C. CMP
• D. CXR

Answer: (A)

Wheezing with severe diarrhea and bright red facial flushing point to carcinoid syndrome from a serotonin-secreting neuroendocrine tumor. The best initial test is a 24-hour urinary level of 5-hydroxyindoleacetic acid (5-HIAA), the main metabolite of serotonin. Elevated 5-HIAA confirms excess serotonin production; dietary restrictions are important during collection to avoid false positives from serotonin-rich foods. If this confirms the syndrome, imaging studies can then be used to locate the tumor. The other tests don’t specifically diagnose carcinoid syndrome: they may provide additional information about anatomy or general health, but they aren’t initial confirmatory tests for serotonin overproduction.