This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Physiology
| HIAA urine levels are suggestive of 
Select and explain. 
A. Carcinoid tumors, B. Colon cancer, C. Malignant melanoma, D. None of the above
A: Carcinoid tumors
Answer: A: Carcinoid tumors 
Explanation: Patients with renal disease may have falsely low 5-HIAA levels in the urine. 5-HIAA is increased in untreated patients with malabsorption, who have increased urinary tryptophan metabolites. Such patients include those with celiac disease, tropical sprue, Whipple disease, stasis syndrome, and cystic fibrosis. Ref: guyton and hall textbook of medical physiology 12 edition