For a urinary tract infection, which test result best demonstrates infection is present?

• A. Urine output increases
• B. Absence of bacteria on urine culture
• C. Bacteria present on urine culture
• D. Red blood cell count normal

Answer: (C)

In diagnosing a urinary tract infection, the key evidence is growth of bacteria in the urine culture. When bacteria are present and growing in the culture, it shows there are viable pathogens in the urinary tract, which is what defines an infection. The other results don’t indicate infection—urine output can vary for many reasons and isn’t specific to infection, a normal red blood cell count in blood isn’t informative about a UTI, and absence of bacteria on culture argues that infection isn’t present. In practice, a positive culture demonstrating significant bacteriuria provides the strongest confirmation of infection, often interpreted alongside symptoms and other urinalysis findings.