Which combination best supports a urinary tract infection on urinalysis?

• A. Positive nitrite and/or leukocyte esterase with significant pyuria and sometimes bacteria on sediment.
• B. Absence of nitrite or leukocyte esterase with no pyuria.
• C. Proteinuria alone.
• D. Crystalluria alone.

Answer: (D)

Urinary tract infections are best identified on urinalysis when there is clear evidence of infection plus an inflammatory response in the urine. Bacteria that convert nitrate to nitrite are common culprits in UTIs, so a positive nitrite result points to bacterial presence. Leukocyte esterase signals white blood cells in the urine, and significant pyuria (increased white blood cells) shows active inflammation. Finding bacteria on sediment confirms that organisms are present. When these pieces come together—nitrite and/or leukocyte esterase with substantial pyuria and bacteria on the sediment—the combination strongly supports a urinary tract infection.

Crystalluria alone indicates crystals in the urine, which can occur with concentration changes or stone disease and does not by itself prove an infection. Proteinuria by itself is not specific for infection, and an absence of nitrite or leukocyte esterase with no pyuria suggests no infection.