What is another name for muddy brown casts observed in urine?

• A. Hyaline casts
• B. White blood cell casts
• C. Pigmented granular casts composed of renal tubular epithelial cells
• D. Epithelial casts

Answer: (C)

Muddy brown casts are pigmented granular casts formed by necrotic renal tubular epithelial cells and pigment debris. In acute tubular necrosis, tubular epithelial cells slough into the tubular lumen, and pigment from cell breakdown (and sometimes hemoglobin or myoglobin) makes these casts appear dark and granular—hence the muddy brown look. This is why the best description is pigmented granular casts composed of renal tubular epithelial cells.

Hyaline casts are colorless and nonspecific, often seen with low urine flow or dehydration. White blood cell casts point to inflammation or infection of the kidneys (pyelonephritis or interstitial nephritis). Epithelial casts can occur with tubular injury but lack the pigmented granular appearance that characterizes muddy brown casts.