During early life, clinical manifestations of urinary tract infection (UTI) are nonspecific and definitive diagnosis through urine culture is often late. It is essential to have rapid and reliable diagnostic tests to guide initial treatment. We compared the diagnostic effectiveness of the urine dipstick, urine sediment, and Gram stain in infants with suspected UTI.

This was a retrospective study conducted by reviewing medical records of patients admitted to the pediatric emergency service during the past five years. We included patients aged up to 24 months with symptoms suggestive of UTI, in which a urine sample was obtained by bladder catheterization to perform urine dipstick, urine sediment, gram stain and urine culture. The presence of leukocyte esterase and nitrites of 1+ or greater by dipstick were considered positive. Leukocyturia was defined as >10 leukocytes per high power field in centrifuged urine; and bacteriuria as the microscopic visualization of any number of bacteria. Gram stain positivity was defined as the isolation of more than 1 bacteria per high power field of any organism in centrifuged fresh urine. The results of these tests were compared with the urine culture as gold standard (positive if >10,000 cfu/mL of a single pathogen). We determined the sensitivity, specificity, positive and negative predictive value, for each of the parameters analyzed. We also compared the results of Gram stain by stratifying patients according to age group (£3 months and >3 months).

During the 5-year study period, 980 patients met inclusion criteria; 430 were girls and mean age was 6 months. Urine culture was positive in 558 cases. Urine dipstick showed leukocyte esterase to be the most sensitive parameter, although nitrites were the most specific (Table I). Similar values were found for the presence of leukocytes and bacteria in the urinary sediment. Gram stain showed the highest diagnostic effectiveness. There were no differences of the value of gram stain in those below and above 3 months of age.

Screening tests are essential to guide diagnosis and initial treatment of UTI in children until the results of urine cultures become available [1,2]. Urine dipstick has been reported to have lower sensitivity in incontinent children, as decreased nitrite production and a less intense inflammatory response due to more frequent urination [3]. This is confirmed in our series. While urine dipstick is a fast and affordable method for initial diagnosis in the emergency department [4], its sensitivity was 80%. Similarly the diagnostic utility of urine sediment was also limited. In contrast, gram stain provided a higher sensitivity and specificity applicable not only to children under 3 months but extendable to 24 months, and was thus a reliable guide for initial antibiotic treatment [5].

Our results show that gram stain was the diagnostic tests of choice for decision making in infants with suspected UTI until the results of urine culture are available.