Which is most likely source of RBC cast in Urinalysis?

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