Which combination of urine findings provides presumptive evidence of a bacterial urinary tract infection?

• A. Leukocytes and a negative nitrite
• B. No leukocytes and positive nitrite
• C. Leukocytes and a positive nitrite
• D. Proteinuria with blood

Answer: (C)

The key idea is that a bacterial urinary tract infection tends to provoke an inflammatory response in the urinary tract (leukocytes in the urine) and is often caused by bacteria that reduce nitrates to nitrites (positive nitrite test). Seeing both leukocytes and nitrite together on a urine dipstick is the strongest presumptive indication of a bacterial infection because it combines evidence of the host response (pyuria) with evidence of the bacterial metabolic activity (nitrate reduction).

Leukocytes alone can appear with noninfectious inflammation or contamination; nitrite alone can occur with some bacteria that reduce nitrates but without a robust inflammatory response. Proteinuria with blood isn’t specific for infection and can reflect other kidney or bladder conditions. So the combination of leukocytes plus a positive nitrite result best supports a bacterial UTI.