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Urine Specific Gravity and the Accuracy of Urinalysis
Nader Shaikh1, Margaret F Shope2, Marcia Kurs-Lasky2
1Division of General Academic Pediatrics, University of Pittsburgh Medical Center, Children's Hospital of Pittsburgh and School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania nader.shaikh@chp.edu.
Insights
Urine specific gravity impacts urinalysis accuracy for pediatric urinary tract infection (UTI) screening. However, considering urine specific gravity in clinical decisions had minimal effect on antibiotic treatment for children with suspected UTI.
Area of Science:
- Pediatric Nephrology
- Clinical Microbiology
- Diagnostic Accuracy
Background:
- Previous research indicated varying optimal cutoffs for urine white blood cell counts based on urine dilution.
- The clinical significance of urine specific gravity in interpreting urinalysis results for pediatric urinary tract infections (UTIs) requires further investigation.
Purpose of the Study:
- To validate findings on differing accuracy of urine tests in dilute versus concentrated samples.
- To assess the impact of urine specific gravity (SG) on clinical management of pediatric UTIs.
Main Methods:
- Retrospective analysis of 10,078 children under 24 months presenting to the emergency department over 5 years.
- Evaluation of screening test accuracy (leukocyte esterase, white blood cell count, nitrite) in dilute and concentrated urine.
- Modeling the impact of urine SG on antibiotic treatment decisions in a hypothetical cohort.
Main Results:
- Positive likelihood ratios for leukocyte esterase were similar in dilute and concentrated urine.
- Positive likelihood ratio for urine white blood cell count was higher in dilute urine; for nitrite, it was lower.
- Predictive models incorporating urine SG showed minimal changes in antibiotic treatment rates.
Conclusions:
- Urine specific gravity affects the diagnostic accuracy of certain urinalysis components for pediatric UTIs.
- Despite influencing test accuracy, incorporating urine SG into clinical decision-making had a negligible impact on antibiotic prescribing for children.
Background:
A recent study in young infants found that different cutoffs maximized the accuracy of the urine white blood cell count in dilute versus concentrated urine samples. We aimed to confirm this finding and to determine its impact on clinical care.
Methods:
We conducted a retrospective analysis of data gathered on consecutive children <24 months of age with visits to the emergency department during a 5-year period. We evaluated the accuracy of screening tests for urinary tract infection (UTI) in dilute and concentrated urine samples. We also calculated the number of children who would have been treated differently in a hypothetical cohort of 1000 children presenting with fever had urine specific gravity (SG) been taken into consideration.
Results:
We included 10 078 children. The ability to rule in UTI (as measured by the positive likelihood ratio [LR]) was similar in dilute and concentrated urine for the leukocyte esterase test (11.76 vs 10.71, respectively). The positive LR for urine white blood cell count per high-powered field was higher in dilute urine (9.83 vs 6.12). In contrast, the positive LR for the nitrite test was lower in dilute urine (20.54 vs 47.44). Despite these differences, we found little change in the number of children treated with antibiotics in predictive models that took urine SG into consideration.
Conclusions:
Although we found that urine SG influences the accuracy of some components of the urinalysis, its inclusion in the decision-making process had negligible effect on the clinical care of children with UTI.
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