Medullary sponge kidney may present with which finding?

• A. Sterile pyuria
• B. Proteinuria
• C. Hematuria without stones
• D. WBC casts

Answer: (A)

Sterile pyuria is the finding most associated with medullary sponge kidney. This congenital abnormality involves dilated, cystic collecting ducts in the renal medulla, which predisposes to sterile inflammation and stone formation. The inflammation can shed white blood cells into the urine without any bacteria growing on culture, producing sterile pyuria. WBC casts would suggest a tubular or interstitial infection, and proteinuria is not a defining feature of this condition. Hematuria can occur, especially with stones, but the presence of leukocytes without bacterial growth—sterile pyuria—is the classic clue pointing toward medullary sponge kidney.