WBC casts in urine most often indicate which condition?

• A. Lower UTI (cystitis)
• B. A renal/upper urinary tract infection such as pyelonephritis or interstitial nephritis
• C. Urolithiasis
• D. Bladder cancer

Answer: (B)

WBC casts in urine signal inflammation or infection inside the kidney tubules and renal parenchyma. They form when white blood cells enter the tubules and mix with tubular proteins (like Tamm-Horsfall protein) to create cylindrical casts that are excreted in the urine. That pattern points to upper urinary tract involvement, such as acute pyelonephritis or tubulointerstitial nephritis.

Lower urinary tract infections, like cystitis, affect the bladder and urethra and usually show leukocytes or bacteria in the urine, but not these tubular casts. Urolithiasis can cause pain and blood in the urine but doesn’t typically produce WBC casts. Bladder cancer often presents with hematuria and other urinary symptoms rather than casts. So the presence of WBC casts most strongly indicates renal/upper tract infection or inflammation.