Radiological Studies
Renal Ultrasound (RUS)
Recent studies have questioned the value of performing routine RUS after a first-time UTI because of the low sensitivity in detecting vesicoureteral reflux (VUR) and a lack of significant influence in altering management (21,22). Patients who have had a normal late (30-32 weeks’ gestation) prenatal ultrasound with a good view of the kidneys may not require a repeat postnatal renal ultrasound (21,22). Further studies are needed to evaluate the costs and value of routine RUS. Until these studies are completed, renal and bladder ultrasound early during hospitalization continues to be recommended for all patients admitted with a first-time UTI to identify hydronephrosis, duplicating collecting systems, ureteral dilatation, calculi, and other structural anomalies.
Voiding Cystourethrogram (VCUG) or Radionuclide Cystography (RNC)
Either a VCUG or RNC should be performed to detect vesico-ureteral reflux in infants and young children. The AAP practice parameter and more recent literature clearly state the need for this evaluation in children under the age of 2 years (2,21). Additional data on incidence of anomalies by age suggest studying children under the age of 6 years (23,24). Recommendations for evaluation of children over age 6 may vary depending on age, patient, and family history, and comorbidities. Alternate methods such as voiding sonogram may also be options for this age group, and is not part of this discussion (25).
RNC exposes the patient to less radiation but does not show urethral or bladder anomalies. RNC is more often used for females with normal RUS and no voiding dysfunction, or to follow the progress of known VUR. The VCUG is often preferred because it provides more anatomic detail and is better for grading VUR and demonstrating posterior urethral vales in males (26). It is suggested that infants with antenatal renal pelvis dilation who have 2 normal renal sonograms in the first month of life are at low risk for abnormalities and may not require a VCUG (27). The rate of detection of VUR with a first episode of UTI does not increase when the VCUG is done early, within the first 7 days of diagnosis (28,29). Performing the VCUG as an inpatient should be considered if outpatient follow-up is of significant concern, or if the RUS suggests bilateral ureteral obstruction. If done as an inpatient procedure, it should be performed preferably during day 3–5 of antibiotic therapy and when the patient is clinically responding to the appropriate antibiotic. The overall value of the VCUG is being reviewed, as its usefulness is most significant only if VUR antimicrobial prophylaxis is effective in reducing reinfections and renal scarring (21,30). Until further studies are performed, the VCUG should continue as part of the initial UTI evaluation for infants and young children.
Renal Cortical Scintigraphy (RCS)
This is the imaging study of choice for the detection of acute pyelonephritis and renal scarring. As children are treated for presumptive upper-tract infection empirically, DMSA scan for diagnosis of pyelonephritis has limited utility (21). Scans have more often been performed at 6 months’ postinfection to document scar formation. Hoberman demonstrated that only 15% of children with abnormal scintigraphy at diagnosis have renal scarring on repeat RCS at 6 months. The importance of these scars is unclear. Association of scars with ultimate development of hypertension, renal insufficiency, and end-stage renal disease is based on studies performed in the 1980s using intravenous pyelogram. RCS is much more sensitive, finding more minor scars of uncertain significance.
click for large version
click for large version
Table 3 may be of value when considering imaging options.
Other Considerations
CRP and PCT use in UTI have been evaluated by Pratt. Values at diagnosis are potentially helpful in ruling out scar formation at 6 months’ postinfection. Values under 1.0 ng/mL for PCT and 20 mg/L for CRP had a negative predictive value of 97.5% and 95%, respectively (31). Further studies are warranted to confirm the usefulness of these inflammatory markers to rule out future scar formation.