Reliability of the urinalysis for predicting urinary tract infections in young febrile children

Background: Urinary tract infections (UTIs) are a common source of bacteria l infection among young febrile children. Clinical variables affecting the sensitivity of the urinalysis (UA) as a screen for UTI have not been previo usly investigated. The limited sensitivity of the UA for detecting a UTI re quires 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 fbr its use should be optimized. Objectives: To determine how the sensitivity of the standard UA as a screen ing test for UTI varies with age, and to determine the clinical situation t hat necessitates the collection of a urine culture regardless of the UA res ult. Methods: Retrospective medical record review of patients younger than 2 yea rs with fever (greater than or equal to 38 degreesC) seen in the emergency department during a period of 65 months. All urine cultures were reviewed f or the collection method, isolates, and colony counts. A UA result was cons idered positive if the presence of 1 of the following was detected: leukocy te esterase, nitrite, or pyuria (greater than or equal to5 white blood cell s per high power field). Patients who had a paired UA and urine culture wer e used to calculate the sensitivity, specificity, and likelihood ratios of the UA. The prevalence of UTIs was also subcategorized by age, race, sex, a nd fever. Results: Medical records of 37450 febrile children younger than 2 years wer e reviewed. Forty-four percent were girls. Median age and temperature were 10.6 months and 38.8 degreesC. A total of 11089 patients (30%) had urine cu ltures 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 wa s 92% (95% CI, 91%-92%). The likelihood ratios for a positive UA and negati ve UA. were 10.6 (95% CI, 10.0-11.2) and 0.19 (95% CI, 0.18-0.20), respecti vely. 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 patien ts, 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 te mperature at or above 39 degreesC compared with those whose temperature was between 38.0 degreesC and 38.9 degreesC. The greatest prevalence of UTI (1 3%) was found among white girls younger than 6 months with a temperature at or greater than 39 degreesC. The posttest probability of a UTI in the pres ence 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%) an d does not vary with age in febrile children younger than 2 years. The prev alence of UTI varies by age, race, sex, and temperature. A negative likelih ood ratio and estimates of prevalence can be used to calculate the risk of missing a UTI due to a false-negative UA result.