This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous (Endocrinology), Subject name: Medicine
Best test for diagnosis of Carcinoid tumor: 
Select and explain. 
A. 24 hour urinary 5H.I.A.A, B. 24 hour catecholamines, C. 24 hour vaniylmandelic acid levels, D. 24 hour metanephrine levels
A: 24 hour urinary 5H.I.A.A
Answer: A: 24 hour urinary 5H.I.A.A 
Explanation: Ans. (a) 24 hour urinary 5H.I.A.ARef: Harrison 19th ed. 1564-65* 5-HLAA is the major urinary metabolite of serotonin, a ubiquitous bioactive amine. Serotonin, and consequently 5-HLAA, are produced in excess by most carcinoid tumors, especially those producing the carcinoid syndrome of flushing, hepatomegaly, diarrhea, bronchospasm, and heart disease.