Which finding on microscopic urinalysis is most consistent with a glomerular source of injury?

Which finding on microscopic urinalysis is most consistent with a glomerular source of injury?

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

Answer: (D)

Red blood cell casts indicate glomerular injury because they form when red cells leak through injured glomerular capillaries and are trapped within a Tamm-Horsfall protein–rich matrix in the renal tubules. This combination—RBCs in a cast—is highly specific for bleeding originating at or above the level of the glomerulus, such as glomerulonephritis or other glomerular diseases. Oval fat bodies reflect lipid-laden tubular cells and are more associated with nephrotic-range proteinuria and lipiduria, not specifically glomerular bleeding. Hyaline casts are non-specific and can occur with dehydration or concentrated urine. Cholesterol crystals can be seen in lipiduria seen with nephrotic states but do not point to glomerular bleeding in particular. So, the presence of red blood cell casts best points to a glomerular source of injury.

Red blood cell casts indicate glomerular injury because they form when red cells leak through injured glomerular capillaries and are trapped within a Tamm-Horsfall protein–rich matrix in the renal tubules. This combination—RBCs in a cast—is highly specific for bleeding originating at or above the level of the glomerulus, such as glomerulonephritis or other glomerular diseases.

Oval fat bodies reflect lipid-laden tubular cells and are more associated with nephrotic-range proteinuria and lipiduria, not specifically glomerular bleeding. Hyaline casts are non-specific and can occur with dehydration or concentrated urine. Cholesterol crystals can be seen in lipiduria seen with nephrotic states but do not point to glomerular bleeding in particular. So, the presence of red blood cell casts best points to a glomerular source of injury.