Does the WBC count, age, or sex predict which febrile children from 90 days to 36 months of age will have a positive urine culture?

Abstract

Study objectives: The purpose of this study is to determine whether the WBC count, age, or sex is predictive of a positive urine culture in children aged 90 days to 36 months who present to the emergency department (ED) with fever. Methods: This prospective study was conducted at an academic ED that treats 16,000 pediatric patients per year. Consecutive enrollment of subjects was performed by the principal investigator when the principal investigator was present. Patients were eligible if they were aged 3 to 36 months, had a rectal temperature of 103°F (39.4°C) or greater, were immunocompetent, did not receive antibiotics before evaluation, and did not have otitis media or pneumonia on physical examination. Eligible patients were evaluated by physical examination, CBC count, blood culture, catheter-obtained urine analysis and culture, and chest radiography. Results: Over a 17-month period, 119 patients were enrolled. Eight patients (6.7%) had a positive urine culture result. Six (9.7%) of the 62 male patients had a positive urine culture result compared with 2 (3.5%) of the 57 female patients. This was not significant. The mean WBC count in the group with a positive culture result was slightly lower than the group with a negative culture result (12.6 versus 13.5; <i>P</i>=not significant). Of the 8 patients with a positive urine culture result, 5 (63%) had a WBC count less than 15,000, and all had a WBC count less than 20,000. Patients younger than 6 months had a higher rate of urinary tract infection than those older than 6 months (16.6% versus 4.2%; <i>P</i>=.029). However, the sensitivity, specificity, and likelihood ratios showed that age was not very useful as a discriminatory test to predict urinary tract infection (sensitivity 62.5, specificity 74.8, positive likelihood ratio 2.48, negative likelihood ratio .50). Conclusion: There was no significant difference in the rate of urinary tract infection according to WBC count or sex. There was a significantly higher rate of urinary tract infection in patients younger than 6 months compared with patients older than 6 months. The use of these criteria for evaluating patients at risk for urinary tract infection is limited by the sensitivity and specificity of this factor.