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: Medicine
A boy is suffering from acute pyelonephritis. Most specific urinary finding will be- 
Select and explain. 
A. W.B.C. casts, B. Leucocyte esterase test, C. Nitrite test, D. Bacteria in gram stain
A: W.B.C. casts
Answer: A: W.B.C. casts 
Explanation: Answer is A (W.B.C) Presence of W.B.0 cast in urine of patients with suspected pyelonephritis is considered pathognomic. 'Leucocyte casts (W.B. C cast) are present in the urine of some patients with Pylonephritis and the detection of these is considered pathognomic'