In the context of urinary tract infections, which urinalysis finding combination supports infection?

• A. Positive nitrite alone confirms infection; leukocyte esterase is noninformative.
• B. Leukocyte esterase alone confirms infection; nitrite is noninformative.
• C. Positive nitrite and leukocyte esterase always indicate infection; however this is not quite accurate.
• D. Positive nitrite suggests nitrate-reducing bacteria; leukocyte esterase indicates pyuria; together support a urinary tract infection.

Answer: (D)

In a urinary tract infection, you’re looking for both evidence of bacteria and the body’s response in the urine. The nitrite test detects bacteria that convert nitrates to nitrites; a positive result points to nitrate-reducing organisms, most commonly the Gram-negative rods such as E. coli. Leukocyte esterase measures an enzyme released by white blood cells, so a positive result indicates pyuria, meaning white blood cells are present in the urine and inflammation is happening.

Why this combination is the best clue: nitrite shows bacterial metabolism, while leukocyte esterase shows the immune response to those bacteria. Each test has limitations—some UTI-causing bacteria don’t reduce nitrate well and may yield a false-negative nitrite, and leukocyte esterase can be positive in other inflammatory conditions or due to contamination. When both tests are positive, they complement each other and together strongly support a urinary tract infection.

So, a positive nitrite implies nitrate-reducing bacteria are present; leukocyte esterase indicates pyuria; and together they provide supportive evidence of an infection.