Which urinalysis finding is diagnostic for glomerulonephritis?

• A. Oval fat bodies
• B. Hyaline casts
• C. Cholesterol crystals
• D. Red blood cell casts

Answer: (D)

Red blood cell casts indicate bleeding from the glomeruli, which is a hallmark of glomerulonephritis. When the glomerular filtration barrier is inflamed and damaged, red blood cells leak into the filtrate. As the filtrate moves through the tubules, these RBCs can get trapped in a matrix of proteins to form casts. Finding RBC casts means the origin of the blood is glomerular, not from somewhere lower in the urinary tract, making it the most specific urinalysis sign for glomerulonephritis.

Oval fat bodies point to nephrotic-range proteinuria and lipiduria, not a nephritic process. Hyaline casts are nonspecific and can appear in many conditions or even with concentrated urine. Cholesterol crystals aren’t a typical diagnostic feature for GN.