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Reliability of the Urinalysis for Predicting Urinary Tract Infections in Young Febrile Children
Richard Bachur, MD;
Marvin B. Harper, MD
Arch Pediatr Adolesc Med. 2001;155:60-65.
Background Urinary tract infections (UTIs) are a common source of bacterial infection
among young febrile children. Clinical variables affecting the sensitivity
of the urinalysis (UA) as a screen for UTI have not been previously investigated.
The limited sensitivity of the UA for detecting a UTI requires that a urine
culture be obtained in some children regardless of the UA result; however,
a proper urine culture requires an invasive procedure, so the criteria for
its use should be optimized.
Objectives To determine how the sensitivity of the standard UA as a screening test
for UTI varies with age, and to determine the clinical situation that necessitates
the collection of a urine culture regardless of the UA result.
Methods Retrospective medical record review of patients younger than 2 years
with fever ( 38°C) seen in the emergency department during a period
of 65 months. All urine cultures were reviewed for the collection method,
isolates, and colony counts. A UA result was considered positive if the presence
of 1 of the following was detected: leukocyte esterase, nitrite, or pyuria
(5 white blood cells per high power field). Patients who had a paired
UA and urine culture were used to calculate the sensitivity, specificity,
and likelihood ratios of the UA. The prevalence of UTIs was also subcategorized
by age, race, sex, and fever.
Results Medical records of 37 450 febrile children younger than 2 years
were reviewed. Forty-four percent were girls. Median age and temperature were
10.6 months and 38.8°C. A total of 11 089 patients (30%) had urine
cultures obtained. The sensitivity of the UA was 82% (95% confidence interval
[CI], 79%-84%) and did not vary by age subgroups. The specificity of UA was
92% (95% CI, 91%-92%). The likelihood ratios for a positive UA and negative
UA were 10.6 (95% CI, 10.0-11.2) and 0.19 (95% CI, 0.18-0.20), respectively.
Prevalence of UTI was 2.1% overall (2.9% for girls and 1.5% for boys, respectively).
Among girls, the prevalence of UTI was 5.0% in white patients, 2.1% in Hispanic
patients, and 1.0% in black patients. Among boys, the prevalence was 2.2%
in Hispanic patients, 1.4% in white patients, and 0.8% in black patients.
Higher prevalence was also seen among patients with a temperature at or above
39°C compared with those whose temperature was between 38.0°C and
38.9°C. The greatest prevalence of UTI (13%) was found among white girls
younger than 6 months with a temperature at or greater than 39°C. The
posttest probability of a UTI in the presence of a negative UA can be calculated
using the negative likelihood ratio and the patient-specific prevalence of
UTI. When the prevalence of UTI is 2%, 1 UA among 250 will produce a false-negative
test result.
Conclusions The sensitivity of the standard UA is 82% (95% CI, 79%-84%) and does
not vary with age in febrile children younger than 2 years. The prevalence
of UTI varies by age, race, sex, and temperature. A negative likelihood ratio
and estimates of prevalence can be used to calculate the risk of missing a
UTI due to a false-negative UA result.
From the Divisions of Emergency Medicine (Drs Bachur and Harper) and
Infectious Diseases (Dr Harper), Children's Hospital, Boston, Mass.
Corresponding author and reprints: Richard Bachur, MD, Division of
Emergency Medicine, Children's Hospital, 300 Longwood Ave, Boston, MA 02115
(e-mail: bachur{at}tch.harvard.edu).
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