This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Small & Large Intestine, Subject name: Surgery
Increased level of 5 HIAA is seen in which disease: 
Select and explain. 
A. Carcinoid tumor, B. Phenylketonuria, C. Pheochromocytoma, D. Gastrinoma
A: Carcinoid tumor
Answer: A: Carcinoid tumor 
Explanation: Ans. (a) Carcinoid tumorRef: Bailey and Love 27th edition, Page 1251/Sabiston 20th edition, Page 1273Diagnosis of carcinoid tumors (NET):* NET produce serotonin in enormous amount -- which is then metabolized in lungs and liver to inactive product known as 5-hydroxyindoleaceticacid.* Increased urinary levels of 5-HIAA in 24 hours urinary samples is used to diagnose Carcinoid tumor. It is more specific to diagnose. Sensitivity is low.* A combination of 5HIAA and Chromogranin A is used to diagnose the tumor with increased sensitivity and specificity* Chromogranin A is better than 5 HIAA in diagnosis as alone.* Now a new combination of Chromogranin A + N-terminal pro brain natriuretic peptide (NT-pro BNP) to diagnose as well as to show the worse survival of the patients.