Diagnostic Accuracy of the Urinalysis for Urinary Tract Infection in Infants <3 Months of Age

Abstract

The 2011 American Academy of Pediatrics urinary tract infection (UTI) guideline suggests incorporation of a positive urinalysis (UA) into the definition of UTI. However, concerns linger over UA sensitivity in young infants. Infants with the same pathogenic organism in the blood and urine (bacteremic UTI) have true infections and represent a desirable population for examination of UA sensitivity.

Diagnosis of Urinary Tract Infections in Children

“…As a compromise, if it is not possible for a laboratory to include a Gram stain or hemocytometer WBC count, some laboratories move the reporting threshold for a significant bacterial countdown to Ն10 4 CFU/ml (Ն10 7 CFU/liter in SI units) or even lower. This practice is supported by a recent study (17) showing that, in infants with bacteremic UTI (not neutropenic), which by definition excludes infants with contaminated urine cultures or asymptomatic bacteriuria, either the leukocyte esterase (LE) test or the nitrite test had a sensitivity of 97.6% and a specificity of 93.9% in detecting UTI, which is much higher than those values previously reported in this population. Standard microscopic detection of pyuria showed a similar sensitivity, but the specificity was considerably lower (around 65%), which probably reflects the fact that various sub- optimal definitions using centrifuged urine samples were used.…”

“…Furthermore, combined with the data from Schroeder et al (17), which showed the excellent performance of the dipstick in predicting bacteremic UTIs in infants less than 3 months of age, these studies suggest that microscopic methods, such as Gram stain and hemocytometer WBC counts, may be supplanted by either manual or automated methods for the detection of pyuria or bacteriuria in children. Whether these findings hold true if a lower threshold for significant bacteriuria is used in children, i.e., 10 4 CFU/ml, and how different automated testing systems compare to one another at different bacterial thresholds remain to be studied.…”

“…In contrast to the AAP guidelines, we feel that there is good evidence from multiple studies providing compelling evidence for the significance of counts between 10 4 and 5 ϫ 10 4 CFU/ml in a significant proportion of children with UTIs (7% to 10%) (2,11,17,(30)(31)(32). To capture these true UTIs and manage them appropriately without compensatory overdiagnosis, it is necessary to lower the diagnostic threshold to Ն10 4 CFU/ml and to accompany this analysis with a rapid, simple, and reliable detector of significant pyuria.…”

“…Although the hemocytometer WBC counting method is regarded as the most reliable, standard microscopy may also be helpful. Given the recent evidence for the utility of the LE test in infants (17), it may not be necessary for the pediatric microbiology laboratory to perform microscopy for pyuria and bacteriuria (especially the resource-intensive hemocytometer WBC count). Adjunctive rapid urinalysis testing for LE and nitrites at point of care or in the core or microbiology laboratory (manual or automated) may be the only necessary additional test to urine culture in determining the clinical significance of urine culture results with high degrees of sensitivity and specificity.…”

Risk of Misinterpretation and Limitation of the Diagnostic Accuracy

“…However, few would disagree that bacteremic UTI (isolation of the same pathogenic organism from the blood and urine) represents true infection. Because of the entities of asymptomatic bacteruria and contamination, the lack of a reliable gold standard for the diagnosis of UTI will be a perpetual problem, 1 and we believe that bacteremic UTI offers a unique way to assess the performance of the UA in an infant who has a true infection.…”