Urinalysis More Sensitive in Young Infants Than Thought

Troy Brown, RN

May 25, 2015

Urinalysis (UA) in young infants with bacteremic urinary tract infection (UTI) is more sensitive than previous research suggested it was in infants with UTI in general, according to new research.

"The 2011 American Academy of Pediatrics'...UTI guideline suggests that the diagnosis of UTI should require an abnormal UA in addition to a positive urine culture," write Alan R. Schroeder, MD, from the Department of Pediatrics, Santa Clara Valley Medical Center, San Jose, California, and colleagues. "However, these guidelines do not include infants <2 months, and young infants with a negative UA and a positive urine culture are generally considered to have UTI."

To better characterize the accuracy of UA, the authors examined UA and urine culture results in infants with bacteremic UTI.

"Bacteremic UTI represent a unique and desirable condition in which to assess the sensitivity of the UA. Infection with the same organism in the blood and urine renders contamination or asymptomatic bacteriuria extremely unlikely, thereby minimizing the probability that the urine culture represents a false positive," the authors explain. They report their findings in an article published online May 25 and in the June issue of Pediatrics.

The researchers collected UA results on a cross-sectional sample of 276 infants younger than 3 months with bacteremic UTIs. The infants had been treated at 11 hospital systems. The authors calculated sensitivity using data from 245 infants who had at least a partial UA performed and ≥50,000 colony-forming units/mL identified in the urine culture.

The researchers determined specificity by analyzing UA results from a random sample of 115 infants from the central study site who had negative urine cultures.

The sensitivity of leukocyte esterase was 97.6% (95% confidence interval [CI], 94.5% - 99.2%), and of pyuria (more than three white blood cells per high-power field), it was 96% (95% CI, 92.5% - 98.1%).Only one baby with bacteremic UTI (group B streptococcus) and a complete UA had a completely negative UA.

In those who had negative urine cultures, the specificity of leukocyte esterase was 93.9% (95% CI, 87.9% - 97.5%), and of pyuria, it was 91.3% (95% CI, 84.6% - 95.6%).

"The authors compared the reported rate of [asymptomatic bacteriuria] in infants with the rate of bacteriuria in febrile infants and calculated that [asymptomatic bacteriuria] could account for the apparent low sensitivity of pyuria versus culture," Kenneth B. Roberts, MD, from the University of North Carolina School of Medicine, Chapel Hill, and Cone Health, Greensboro, writes in an accompanying editorial. "They tested the validity of this proposition by studying a group of young infants with true UTI, as determined by the presence of the same organism in urine and blood. In these infants, the sensitivity of pyuria ranged from 96% to 99.5% (depending on the quantitative definition of pyuria), thus confirming its usefulness for diagnosis."

"In young, febrile infants, UTI is the most common serious bacterial infection. This diagnosis drives substantial interventions, including hospitalization for prolonged antibiotic therapy and follow-up urinary imaging," the researchers conclude. "Our study highlights the need to further define the role of the UA in young infants with suspected UTI to minimize the possibility of harm and excessive costs from overtreatment."

The authors and editorialist have disclosed no relevant financial relationships.

Pediatrics. 2015;135:966-971, 1126-1127.

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