RBC casts present in the urine and there is red urine; which condition is most suggested?

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RBC casts in the urine point to bleeding from the glomeruli. When red blood cells leak through damaged glomerular capillaries, they can be carried into the tubules and become embedded in a matrix of Tamm-Horsfall protein, forming RBC casts. This pattern is classic for nephritic processes that injure the glomeruli, such as glomerulonephritis, and it often accompanies visible (gross) hematuria.

In acute tubular necrosis, the typical casts are granular and epithelial cell casts from tubular injury, not RBC casts. Pyelonephritis can have white blood cell casts and pyuria, reflecting infection in the collecting system and renal pelvis, and cystitis mainly shows sterile or microscopic hematuria without RBC casts. Therefore, the combination of visible blood in the urine and RBC casts most strongly suggests glomerulonephritis.