This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
A 29 year male complains of pain in the flank that radiates from the loin to the groin region. The first investigation to be done is - 
Select and explain. 
A. CECT, B. Plain CT Scan, C. USG abdomen, D. Xray Abdomen
C: USG abdomen
Answer: C: USG abdomen 
Explanation: Ans. is C. First investigation is USG>Xray Abdomen IOC is CT Gold standard investigation for renal calculi: Non contrast CT scan