Is Urinalysis Reliable After All for UTI Diagnosis in Young Infants?

Schroeder AR, Chang PW, Shen MW, Biondi EA, Greenhow TL. Diagnostic accuracy of the urinalysis for urinary tract infection in infants <3 months of age. Pediatrics. 2015;135(6):965-971.

Urine culture is the gold standard for the diagnosis of urinary tract infections (UTIs) in children because of the reported suboptimal sensitivity of urinalysis (UA). The 2011 clinical practice guideline on UTIs from the American Academy of Pediatrics (AAP) suggests that the diagnosis of a UTI should include an abnormal UA result and a positive culture result.¹ This approach does not apply to infants younger than 2 months of age; therefore, infants with positive culture and negative UA results still are treated for a presumed infection, and the results are not seen as contamination of the sample or asymptomatic bacteriuria.

With these discrepancies in mind, Schroeder and colleagues sought to calculate the sensitivity of the UA for infants younger than 3 months of age who had bacteremic UTI, since an infection in blood and urine made contamination or asymptomatic bacteriuria less likely. The specificity of UA also was examined.

To accomplish this, a multicenter database of infants younger than 3 months of age (276 infants at 20 hospitals) with bacteremic UTI was analyzed. Infants who had major comorbidities, who had central access, or who received care in an intensive care unit were not included. Data on specific components of the UA were collected, and a uniform collecting system was established to account for variation in the categories used at various institutions. To calculate UA specificity, a sample group of 115 infants with negative urine cultures was analyzed.

When the various components of the UA were reviewed, leukocyte esterase (LE) had the highest sensitivity at 97.6% (95% confidence interval [CI], 94.5%-99.2%), and nitrites had the highest specificity at 100% (95% CI, 96.8%-100%). If a positive UA was defined by pyuria (>3 white blood cells/high-power field [WBC/HPF]) and/or any LE, the sensitivity (99.5%; 95% CI, 98.5%-100%) and specificity (87.8%; 95% CI, 80.4%-93.2%) were both higher than those calculated when using the AAP guideline’s definition of a positive UA (ie, pyuria >3 WBC/HPF or bacteriuria), where sensitivity was 98.3% (95% CI, 95.2%-99.7%) but specificity was only 63.5% (95% CI, 54%-72.3%). A definition that included any positive UA component was highly sensitive (99.4% in infants with complete UAs; 98.4% in infants with incomplete UAs), but was less specific (60%, 95% CI 50.4%-69%) than the aggregate of pyuria and/or LE.

These results show that if the definition of a positive UA included pyuria and/or positive LE, it was highly sensitive and specific. A negative LE and the absence of WBCs in the urine were notably specific (87.8%) in infants with negative urine cultures. UA bacteria demonstrated poor specificity, especially compared with pyuria or LE. The near perfect sensitivity of UA may be explained by spectrum bias, or that the current gold standard (urine culture) is flawed.

The implications of this study are noteworthy. UTIs are the most common serious bacterial infection in febrile infants, and they lead to interventions such as prolonged hospitalizations, antibiotic therapy, and imaging. Requiring a positive UA for diagnosis may lead to overtreatment, creating a risk of harm and increasing health care costs. Further studies are needed to investigate the role of UA in the definition and diagnosis of a UTI in young infants.

Jessica Tomaszewski, MD, is an assistant clinical professor of pediatrics at the Sidney Kimmel Medical College at Thomas Jefferson University in Philadelphia, Pennsylvania, and a hospitalist pediatrician at Nemours/Alfred I. duPont Hospital for Children in Wilmington, Delaware.

Charles A. Pohl, MD—Series Editor, is a professor of pediatrics, senior associate dean of student affairs and career counseling, and associate provost for student affairs at the Sidney Kimmel Medical College at Thomas Jefferson University in Philadelphia.

References

1. American Academy of Pediatrics Subcommittee on Urinary Tract Infection, Steering Committee on Quality Improvement and Management. Urinary tract infection: clinical practice guideline for the diagnosis and management of the initial UTI in febrile infants and children 2 to 24 months. Pediatrics. 2011;128(3):595-610.