Investigations
1st investigations to order
urine dipstick
Test
Urinalysis should be performed within 60 minutes of obtaining specimen. First morning voids may be best for yielding a positive nitrite test. A positive nitrite (bacteriuria) or leukocyte esterase (pyuria) result should be followed by a urine culture.[1][4]
Result
positive leukocyte esterase and/or positive nitrite
urine microscopy
Test
The optimal cut point for diagnosing pyuria varies according to urine concentration in children aged <24 months, from 3 white blood cells (WBCs) per high-power field in dilute urine to 8 WBCs per high-power field in concentrated urine.[47]
Other inflammatory conditions, or the presence of renal stones, may cause pyuria in the absence of UTI.[13]
Presence of any bacteria on microscopy indicates bacteriuria. Morphology and gram-staining characteristics may aid early identification of the causative organism.
Result
>5 WBC/high-power field or any bacteria
Investigations to consider
urine flow cytometry
Test
Alternative test to dipstick testing or microscopy.
Performed on uncentrifuged urine specimens and provides counts of WBCs and bacteria in the urine.[1]
Studies suggest that this technique may have a greater sensitivity and specificity in children than dipstick testing or microscopy; however, it is not yet widely available.[48][49]
Result
presence of leukocytes and bacteria
blood culture
Test
All febrile/systemically unstable neonates (≤28 days of age) and febrile/systemically unstable infants (1-24 months) should have blood cultures taken on presentation.[54] Follow-up blood cultures should be performed for any patient who is still febrile 24 hours after initiation of therapy.
Result
positive for infecting organism
full blood count
Test
Absolute neutrophil count may be used to guide decisions about performing lumbar puncture and starting empirical antibiotic therapy in well-appearing term infants ≤2 months old.[54]
Result
elevated absolute neutrophil count
inflammatory markers
Test
Inflammatory markers may be used to guide decisions about performing lumbar puncture and starting empirical antibiotic therapy in well-appearing term infants ≤2 months old.[54]
Result
elevated C-reactive protein or procalcitonin
fungus urine culture
Test
Consider in immunosuppressed patients.
Urine culture for fungus should be specifically requested; this requires different laboratory techniques compared with standard bacterial culture.[55]
Result
positive for candida
serum creatinine, urea and electrolytes
Test
In patients hospitalised with complicated UTI, serum creatinine, cystatin c, urea and electrolytes, blood pressure measurements, and urine screening for proteinuria should be pursued.
Result
normal or elevated creatinine, cystatin c, and urea
renal and/or bladder ultrasound
Test
Initially performed to look for any anatomical abnormalities of the urinary tract.
Also may be performed to look for evidence of a renal or perinephric abscess when the urinalysis and culture are negative but abdominal pain and fever persist.
The American College of Radiology (ACR) and the American Academy of Pediatrics (AAP) recommend that all infants under 2 months of age should have a renal ultrasound following their first UTI.[5][11]
The AAP and the Canadian Paediatric Society also recommend a renal and bladder ultrasound (RBUS) after the first confirmed febrile UTI for children between 2 and 24 months, and 2 and 36 months of age, respectively.[5][40] European Association of Urology guidelines recommend renal and bladder ultrasound within 24 hours in infants with febrile UTI to exclude obstruction of the upper and lower urinary tract.[1]
In the UK, the National Institute for Health and Care Excellence recommends ultrasound for infants and children with atypical UTI to identify any structural abnormalities. Infants younger than 6 months with first-time UTI who respond well to treatment should have a non-urgent ultrasound within 6 weeks of diagnosis. Ultrasound is also indicated in those aged 6 months to <3 years in the presence of recurrent UTIs.[4]
Result
abnormalities may be present such as dilation of the renal pelvis or ureters, distention of thick-walled bladder, renal stones, ureterocele, bladder wall trabeculation, high post-void residual volume, enlarged rectal diameter; renal abscess: area of radiolucency to the renal parenchyma with local hypoperfusion on colour Doppler; perinephric abscess: hypoechoic fluid
dimercaptosuccinic acid (DMSA) scan
Test
Detects renal scarring and pyelonephritis.
Recommended in children with recurrent or atypical UTI by both UK and US guidelines, 4 to 6 months following the acute infection.[4][11]
May be difficult to distinguish acute changes of pyelonephritis from old renal scarring.
Result
pyelonephritis or renal scarring: focal or diffuse areas of decreased uptake
voiding cystourethrogram (VCUG)
Test
Performed to evaluate for the presence and degree of vesicoureteral reflux (VUR). Also permits evaluation of bladder anatomy and post-void residual volume.
A film during voiding permits visualisation of the urethra and is essential in male children to exclude posterior urethral valves.[50]
The American Academy of Pediatrics recommends that a VCUG is considered in children with abnormal RBUS, atypical causative pathogen, complex clinical course, or known renal scarring.[5] VCUG may also be considered in patients with a family history of VUR or congenital anomalies of kidneys and the urinary tract after first febrile UTI.[5]
Similarly, the European Association of Urology advises that VCUG should only be used if there is a suggestion of high-grade VUR, for example, febrile UTI, abnormal renal ultrasound, and/or non-Escherichia coli infection.[1]
The UK National Institute for Health and Care Excellence recommends VCUG in infants younger than 6 months if they have an abnormal ultrasound, atypical UTI, or recurrent UTI.[4]
Result
if vesicoureteral reflux is present: contrast seen ascending out of the bladder into the upper urinary tract; if posterior urethral valves present: dilation and elongation of the posterior urethra; may reveal ureterocele, bladder polyp or diverticulae, or post-void residual volume
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