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
[{'content': 'Which is most likely source of RBC cast in Urinalysis? \nSelect and explain. \nA. Ureter, B. Kidney, C. Bladder, D. Urethra', 'role': 'user'}, {'content': "Answer: B \nExplanation: The RBCs of glomerular origin are often dysmorphic when examined by phase-contrast microscopy. Irregular shapes of RBCs may also result from pH and osmolarity changes produced along the distal nephron. Hematuria with dysmorphic RBCs, RBC casts, and protein excretion >500 mg/d is viually diagnostic of glomerulonephritis. RBC casts form as RBCs that enter the tubule fluid become trapped in a cylindrical mold of gelled Tamm-Horsfall protein. So the source of RBC Cast is kidney. Ref: Harrison's Internal Medicine, 18th Edition, Page 339", 'role': 'assistant'}]