September 2000
BOSTON - Long considered the gold standard for diagnosing urinary tract infections (UTI), results of a study recently presented at the Pediatric Academic Societies and the American Academy of Pediatrics Joint Meeting confirm that urine culture is still necessary to rule out UTI in young children.
The primary drawback of urine culture is time, said Theresa A. Schlager, MD, of the department of pediatrics at the University of Virginia in Charlottesville. While it generally takes two days to get culture results, urinalysis results may be available while the patient is still in the pediatrician's office.
Schlager and colleagues performed a study to assess the accuracy of standard microscopy without Gram's stain and the dipstick test against urine culture to see if a normal urinalysis could rule out the possibility of UTI in young children.
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"Under the age of 4, ... UTI may be the first sign of a urinary tract abnormality," Schlager said. "For that particular population, you would not like to miss any UTIs. Therefore culture cannot be omitted."
Thirty cultures were positive for 260 children studied. Twenty-one (70% sensitivity) children had a dipstick test that was positive for leukocyte esterase. Five samples were also nitrite positive. Only five of the 230 culture-negative samples were leukocyte-esterase positive (98% specificity).
On the other hand, standard microscopy was not helpful, she said. Twenty-four of the 30 culture-positive samples and 50 of 230 culture-negative samples were positive for bacteruria. Pyuria was noted in 19 culture-positive samples and 49 culture-negative samples.
Combining results of dipstick and standard microscopy, 37% of samples were found positive by urinalysis when the culture was negative, Schlager said.
Standard microscopy was found to be a poor screening test for UTI in young children. In practice, a dipstick analysis and culture is performed when evaluating a young child for UTI. A negative dipstick does not rule out a UTI. A positive dipstick raises suspicion of a UTI and helps determine whether to start antibiotics prior to culture confirmation.
Schlager and colleagues analyzed results of urinalyses and urine cultures in children younger than 4 who were seen during the previous three years for suspected UTI. Only those whose samples had been obtained by in-and-out catheterization were included. Enrollees were not taking antibiotics when the sample was obtained and had to have a healthy urinary tract. Urine samples also had to be sufficient to perform both standard microscopy and the dipstick test.
Positive nitrite or leukocyte esterase was considered as a positive dipstick test. Any bacteria found by standard microscopy were defined as bacteruria, and having at least five white blood cells on high power field was defined as pyuria. Culture results of at least 104 CFU of a uropathogen/mL of urine were defined as positive.
For more information:
- Armengol CE, Hendley JO, Schlager TA. Urinary tract infection in young children cannot be excluded with urinalysis. Session 1009. Presented at the Pediatric Academic Societies and the American Academy of Pediatrics Joint Meeting. May 12-16, 2000. Boston.
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