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 degrees 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 degrees 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 degrees C compared with those whose temperature was between 38.0 degrees C and 38.9 degrees C. The greatest prevalence of UTI (13%) was found among white girls younger than 6 months with a temperature at or greater than 39 degrees 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.