UMEM Educational Pearls

Category: Pediatrics

Title: Does urine concentration effect the diagnosis of urinary tract infection?

Keywords: Pediatrics, urinary tract infection, urine concentration (PubMed Search)

Posted: 4/14/2017 by Jennifer Guyther, MD (Updated: 6/13/2024)
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Question

A recent study suggests that using a lower cut off value of white blood cells in dilute urine, may have a higher likelihood of detecting a urinary tract infection in children.

In dilute urine (specific gravity < 1.015), the optimal white blood cell cut off point was 3 WBC/hpf (Positive LR 9.9).  With higher specific gravities, the optimal cut off was 6 WBC/hpf (Positive LR 10).  Positive leukocyte esterase has a high likelihood ratio regardless of the urine concentration. 

 

Answer

This was a retrospective study of 2700 infants < 3 months old who were evaluated for urinary tract infections (UTI).  The UTI prevalence in this group was 7.8%.  A UTI was defined as at least 50,000 colony forming units/mL from a catheterized specimen.  Test characteristics looked at white blood cell and leukocyte esterase cut-offs, dichotomized into specific gravities: dilute (<1.015) and concentrated (>/=1.015).