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Pediatric Urine Concentration and UA Accuracy

July 13, 2021

Written by Clay Smith

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Children <24 months may still have a UTI even with as few as 3 WBCs/hpf on urine microscopy if the urine is very dilute. Small leukocyte esterase on urinalysis was a powerful positive discriminator at all urine concentrations.

Why does this matter?
We have previously covered the varying diagnostic accuracy of urinalysis (UA) in children based on urine concentration. In a very dilute urine, even a few white blood cells per high-power field (WBCs/hpf) are concerning, whereas it is the opposite in highly concentrated urine. This study takes this concept a step further.

This takes concentration…
This was a retrospective look at 24,171 children under age two years with paired UA and urine culture results; 2,003 (8.3%) had a positive culture. The ideal cut points for WBCs/hpf on microscopic exam varied based on urine concentration. For a specific gravity <1.011, 3 WBCs/hpf had a LR+ of 10.5 and LR- 0.12; specific gravity 1.011 to 1.020, 6 WBCs/hpf had a LR+ 12 and LR- 0.14; for specific gravity >1.020, 8 WBCs/hpf had a LR+ 11.1 and LR- 0.35. Any child who had small leukocyte esterase (LE) on UA had LR+ > 25 at all urine concentrations; LR- for no LE ranged from 0.12 at low specific gravity, 0.15 medium, to 0.41 high.

Pyuria and Urine Concentration for Identifying Urinary Tract Infection in Young Children. Pediatrics. 2021 Feb;147(2):e2020014068. doi: 10.1542/peds.2020-014068.

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