Peds UA Accuracy Varies with Urine Concentration

Short Attention Span Summary

Try and concentrate
More concentrated urine impairs the diagnostic accuracy of UA leukocyte esterase (LE) and microscopic pyuria in kids.  When stratified by specific gravity, the positive likelihood ratio of positive LE or pyuria (>/= 5 WBCs/hpf) for a positive urine culture decreased as the specific gravity increased.  Sensitivity for LE was 74% (average over all urine concentrations) and pyuria >/= 5 WBCs was 80%.  That's why it is very important to obtain a urine culture in children you suspect may have a UTI.  The gist is that if you have dilute urine with positive LE or microscopic pyuria, it is probably a real UTI.  If the urine is concentrated, it's harder to tell.  The authors concluded, "using a lower threshold for pyuria in a dilute urine sample compared with a concentrated sample for the presumptive diagnosis of urinary tract infection may be warranted."

Spoon Feed
If you have dilute urine with positive LE or microscopic pyuria, it is probably a real UTI.  If the urine is concentrated, it's harder to tell.  Less than 5 WBCs in unspun dilute urine may still indicate a UTI.  If you suspect UTI clinically, obtain a culture regardless of UA/micro results.  See the brief, outstanding summary by Ryan Radecki.


Abstract

Ann Emerg Med. 2017 Feb 3. pii: S0196-0644(16)31512-8. doi: 10.1016/j.annemergmed.2016.11.042. [Epub ahead of print]

The Importance of Urine Concentration on the Diagnostic Performance of the Urinalysis for Pediatric Urinary Tract Infection.

Chaudhari PP1, Monuteaux MC2, Shah P3, Bachur RG2.

Author information:

1Division of Emergency Medicine, Boston Children's Hospital, Boston, MA; Harvard Medical School, Boston, MA. Electronic address: pradip.chaudhari@childrens.harvard.edu.

2Division of Emergency Medicine, Boston Children's Hospital, Boston, MA; Harvard Medical School, Boston, MA.

3Division of Emergency Medicine, Boston Children's Hospital, Boston, MA.

Abstract

STUDY OBJECTIVE:

The presence of leukocyte esterase by urine dipstick and microscopic pyuria are both indicators of possible urinary tract infection. The effect of urine concentration on the diagnostic performance of the urinalysis for pediatric urinary tract infection has not been studied. Our objective is to determine whether the urinalysis performance for detecting urinary tract infection varies by urine concentration as measured by specific gravity.

METHODS:

This was a retrospective cross-sectional study of the urine laboratory results of children younger than 13 years who presented to the emergency department during 68 months and had a paired urinalysis and urine culture obtained. Urinary tract infection was defined as pure growth of a uropathogen at standard culture thresholds. Test characteristics were calculated across 4 specific gravity groups (1.000 to 1.010, 1.011 to 1.020, 1.021 to 1.030, and >1.030).

RESULTS:

In total, 14,971 cases were studied. Median age was 1.5 years (interquartile range 0.4 to 5.5 years) and 60% were female patients. Prevalence of urinary tract infection was 7.7%. For the presence of leukocyte esterase and a range of pyuria cut points, the positive likelihood ratios decreased with increasing specific gravity. From most dilute to most concentrated urine, the positive likelihood ratio decreased from 12.1 (95% confidence interval [CI] 10.7 to 13.7) to 4.2 (95% CI 3.0 to 5.8) and 9.5 (95% CI 8.6 to 10.6) to 5.5 (95% CI 3.3 to 9.1) at a threshold of greater than or equal to 5 WBCs per high-power field and presence of leukocyte esterase, respectively. The negative likelihood ratios increased with increasing specific gravity for leukocyte esterase and microscopic pyuria.

CONCLUSION:

For the detection of pediatric urinary tract infection, the diagnostic performance of both dipstick leukocyte esterase and microscopic pyuria varies by urine concentration, and therefore the specific gravity should be considered when the urinalysis is interpreted.

Copyright © 2016 American College of Emergency Physicians. Published by Elsevier Inc. All rights reserved.

PMID: 28169050 [PubMed - as supplied by publisher]