Nephrology Q25

Answer & Critique

Correct Answer: B

Educational Objective: Diagnose glomerulonephritis.

Key Point

Glomerular macroscopic hematuria typically features brown- or tea-colored urine with dysmorphic erythrocytes (or acanthocytes) and/or erythrocyte casts on urine sediment examination.

This patient likely has glomerulonephritis. Glomerular hematuria typically features brown- or tea-colored urine with dysmorphic erythrocytes (or acanthocytes) and/or erythrocyte casts on urine sediment examination. Erythrocyte casts are recognized by their cylindrical or tubular structure and inclusion of small, agranular spherocytes and, when present, are specific for hematuria of glomerular origin.

Isomorphic erythrocytes are of the same size and shape and usually arise from an extraglomerular urologic process causing bleeding into the genitourinary tract, such as a tumor, stone, or infection. Dysmorphic erythrocytes have varying sizes and shapes. Acanthocytes, a specific form of dysmorphic erythrocytes, are characterized by vesicle-shaped protrusions and suggest a glomerular source of bleeding. Acanthocytes and erythrocyte casts are highly specific for glomerulonephritis and exclude an extraglomerular cause of bleeding such as bladder cancer.

Sterile pyuria and leukocyte casts are hallmarks of tubulointerstitial nephritis, which can present acutely or may progress indolently and present as chronic kidney disease of unclear duration. Mild subnephrotic proteinuria also can be seen with interstitial nephritis. The cells comprising a leukocyte cast are larger than erythrocytes and appear more granular. The presence of erythrocyte casts excludes the diagnosis of tubulointerstitial nephritis.

Although this febrile patient has leukocytes (granular cells larger than erythrocytes) on urinalysis and positive leukocyte esterase on dipstick analysis, the presence of erythrocyte casts is specific for glomerulonephritis. This patient has the nephritic syndrome, which is associated with glomerular inflammation resulting in hematuria, proteinuria, and leukocytes in the urine sediment.

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