Which test result would most strongly support a urinary tract infection as the source of fever in a febrile 2-month-old?

Which test result would most strongly support a urinary tract infection as the source of fever in a febrile 2-month-old?

• A. Elevated erythrocyte sedimentation rate
• B. Chest X-ray infiltrate
• C. Positive catheterized urine leukocyte esterase/nitrite
• D. Positive blood culture

Answer: (C)

In a febrile infant, pinpointing the source of fever relies on tests that directly reflect the suspected infection site. A positive catheterized urine test showing leukocyte esterase and nitrite is the strongest evidence for a urinary tract infection because leukocyte esterase indicates pyuria (white blood cells in the urine), and nitrite indicates bacteria that reduce nitrates to nitrites, a pattern typical of common UTI pathogens like E. coli. Using catheterization to obtain the urine makes the result more reliable by reducing contamination. Other findings are less specific: an elevated ESR is a nonspecific marker of inflammation, a chest X-ray infiltrate points to pneumonia, and a positive blood culture shows bacteremia but doesn’t specifically prove the urinary tract is the source. So this urine test result best supports the urinary tract as the fever source.

In a febrile infant, pinpointing the source of fever relies on tests that directly reflect the suspected infection site. A positive catheterized urine test showing leukocyte esterase and nitrite is the strongest evidence for a urinary tract infection because leukocyte esterase indicates pyuria (white blood cells in the urine), and nitrite indicates bacteria that reduce nitrates to nitrites, a pattern typical of common UTI pathogens like E. coli. Using catheterization to obtain the urine makes the result more reliable by reducing contamination. Other findings are less specific: an elevated ESR is a nonspecific marker of inflammation, a chest X-ray infiltrate points to pneumonia, and a positive blood culture shows bacteremia but doesn’t specifically prove the urinary tract is the source. So this urine test result best supports the urinary tract as the fever source.