Red blood cell casts in the urine are most strongly associated with which renal condition?

• A. Glomerulonephritis
• B. Acute tubular necrosis
• C. Interstitial cystitis
• D. Urolithiasis

Answer: (A)

Red blood cell casts form when bleeding originates in the glomeruli and the RBCs pass through damaged glomerular capillaries into the tubular fluid, where they become embedded in a protein matrix to create casts. This pattern reflects glomerular hemorrhage, which is characteristic of glomerulonephritis, where inflammation and injury to the glomeruli increase permeability and allow RBCs to leak into the filtrate. Other conditions can cause blood in the urine, but they don’t typically produce RBC-containing casts: acute tubular necrosis mainly yields granular or tubular epithelial cell casts due to tubular injury; interstitial cystitis involves the bladder and usually presents with pain and bladder symptoms rather than glomerular bleeding; urolithiasis causes hematuria from stone irritation but not the formation of RBC casts. So red blood cell casts in urine most strongly point to glomerulonephritis.