An upper urinary tract infection primarily involves which organ?

• A. Bladder
• B. Kidneys
• C. Urethra
• D. Ureter

Answer: (B)

Upper urinary tract infections involve structures above the bladder, with the kidneys being the primary organ affected. When the kidney is involved, the condition is classically called pyelonephritis and presents with fever, flank or groin pain, and systemic or malaise rather than just urinary symptoms. The ureter is not the main site of infection in an upper tract infection, even though it may be involved along the path of spread. In contrast, infections of the lower urinary tract affect the bladder or urethra, producing dysuria, urgency, and frequency.