Which urinalysis finding most strongly supports a true urinary tract infection?

• A. Positive nitrite and leukocyte esterase
• B. Positive nitrite alone
• C. Cloudy urine alone
• D. pH 9.0 only

Answer: (A)

Evidence of bacterial nitrate reduction together with white blood cell activity in the urine provides the strongest indication of a true urinary tract infection. Nitrite positivity occurs when nitrate-reducing bacteria, typically certain Gram-negative rods, are present and have had time to convert nitrates to nitrites; this makes the finding fairly specific, though not perfect since some pathogens don’t reduce nitrate and because insufficient bladder dwell time can yield a false negative. Leukocyte esterase signals pyuria, reflecting an inflammatory response to infection, and it is sensitive but less specific because sterile inflammation can also raise LE. When both are positive, you have concurrent evidence of bacteria in the urine and an immune response, which together create the strongest diagnostic signal for a UTI. Cloudy urine or a high pH by itself are far less specific and can occur in other conditions, so they don’t support infection as strongly.