White blood cell casts in urine are most indicative of which process?

• A. Tubulointerstitial inflammation or infection
• B. Glomerular bleeding
• C. Nephrotic syndrome
• D. Crystalluria

Answer: (A)

White blood cell casts in urine point to inflammation or infection of the kidney tubules and interstitium. They form when leukocytes enter the tubular lumen and become embedded in a protein cast, signaling a tubulointerstitial process such as pyelonephritis or interstitial nephritis. This contrasts with red blood cell casts, which would suggest glomerular bleeding; nephrotic syndrome, which revolves around heavy proteinuria and lipid changes rather than leukocytes in casts; and crystalluria, which involves crystals rather than leukocyte-containing casts. So the finding most directly indicates a tubulointerstitial inflammatory or infectious process.