MALMO, SWEDEN – Ultrasound of the kidneys and urinary tract in the acute phase of a first urinary tract infection in young children has an unacceptably high false-positive rate, , reported at the annual meeting of the European Society for Paediatric Infectious Diseases.
“Sonography performed 2 weeks after treatment initiation seems to be more reliable,” said Dr. Okarska-Napierala, a pediatrician at the Medical University of Warsaw Children’s Hospital.
Broad agreement exists that imaging is warranted in all children with a first urinary tract infection (UTI), because this infection can be the first signal of a structural abnormality of the kidneys or urinary tract. Abdominal ultrasound is the first-choice imaging modality in this setting because it is noninvasive, widely available, and inexpensive. But there remains controversy – and guidelines differ – regarding when to perform the ultrasound in children with UTI who respond well to therapy. This was the impetus for Dr. Okarska-Napierala and her coinvestigators to launch a prospective, single-center study examining the issue.
“The theory beneath it is the possibility that diffuse inflammation affects the ultrasound picture of the kidneys and urinary tract and may give us false-positive results, so we shouldn’t base our decisions on those results,” she explained.
This theory has been provisionally confirmed by the preliminary results of the study, which is continuing to enroll patients.
To date, the study includes 48 children, mean age 10.4 months, hospitalized for their first UTI. Participation was restricted to patients with no known congenital abnormalities of the kidneys or urinary tract and who were not on antibiotics at enrollment. Of the 48 children, 44 had an Escherichia coli infection. The predominant treatment was a second-generation cephalosporin for a median of 10 days.
On day 1 of treatment all patients underwent an ultrasound exam evaluating kidney size, anterior-posterior renal pelvis diameter, and the urinary tract based upon a grading system for urinary tract dilation developed by multidisciplinary consensus (). The ultrasound exam was repeated 2 weeks later, and again 2 weeks after that.
The most striking findings were a significantly increased kidney size and more prevalent urinary tract dilation on the day 1 ultrasound exam than on repeat ultrasound 2 weeks later. The average length of the left and right kidneys was 67.0 and 64.5 mm, respectively, on day 1, dropping off to 64.3 and 62.0 mm at 2 weeks, with a smaller and statistically nonsignificant further drop-off to 61.9 and 60.0 mm on the week 4 ultrasound.
“We saw a strong correlation between initial kidney size and CRP [C-reactive protein] value: The higher the CRP you have initially, the bigger the kidneys. It’s an interesting finding, but not so very practical. The only practical conclusion is that if we perform ultrasound at this stage and the child has big kidneys, it doesn’t mean anything. We have to check it again later,” she said.
Also, the number of renal units with urinary tract dilation went from 29 on day 1 ultrasound to 20 at 2 weeks and 19 at 4 weeks. Of the 48 children, 28 had urinary tract dilation on day 1, compared with 18 at 2 weeks and 16 at 4 weeks.
“If we look at this practically, if we base our decision on the day 1 ultrasound we would qualify half of all children for voiding cystourethrography, which is harmful, but if we wait 2 weeks to do the ultrasound we would reduce this number by six children. So I think we can call this a clinically significant difference,” she continued.
Of the 48 children, 11 have undergone voiding cystourethrography, revealing 2 mild cases of vesicoureteral reflux, which is the most common congenital abnormality of the urinary tract.
“I would like to emphasize that there is no real benefit in performing an ultrasound exam in children in this acute phase of infection. And there is harm in that we have to repeat the exam later, the parents are worried, the doctor is worried,” Dr. Okarska-Napierala concluded.
She reported having no relevant financial conflicts, and the study was conducted free of commercial support.