Urinalysis Lab Questions

[Arlyne Doepner]

Aurine sample should be obtained for testing before antibiotic therapy is initiated in clinically unstable children who do not have a clear source of infection. In other children, age and clinical findings can be used to determine the need for testing. The physician's overall clinical impression for UTI often misses the diagnosis.

Urine testing is indicated for all acutely ill infants (both febrile and afebrile) who are younger than three months.4,12 For febrile children two to 24 months of age, the 2011 American Academy of Pediatrics (AAP) guideline recommended basing testing decisions on risk factors and absence of alternative sources of infection. However, this guideline was retired in 2021 because of improper use of race as a risk factor and potential for missed diagnoses in Black and non-White children.10,16,17.The UTICalc, a tool developed by the University of Pittsburgh ( ), uses similar risk factors (excluding race) to estimate the risk of UTI in febrile children two to 23 months of age. Testing is recommended when the risk is 2% or greater.

Two observational studies in the United Kingdom raise concern for UTI in unwell but afebrile children. In one study of 597 children younger than five years, absence of fever did not sufficiently rule out UTI.12 A particularly high rate of UTIs was noted in infants younger than three months (12.5%); thus, the authors recommend that all acutely ill children in this age group be tested regardless of symptoms. A second observational study of 2,740 children younger than five years found that the following clinical findings were associated with an increased risk of UTI: pain or crying with urination, malodorous urine, history of UTI, absence of cough, severe illness, lack of ear abnormalities, and abdominal tenderness on examination.14 Lack of fever was not useful for ruling out UTI. This study was limited by underrepresentation of children younger than two years, who comprised only 6.5% of the study population.

A study evaluating the diagnostic accuracy of UTI symptoms found that the decision to perform urine testing in verbal children older than 24 months should be based on sex, circumcision status, and symptoms.15 In girls and uncircumcised boys with urinary frequency, dysuria, abdominal pain or tenderness, back pain, or new-onset incontinence, the probability of UTI is 18% to 30%, and urine testing should be performed. If these symptoms are not present, the probability of UTI is low, and testing is not indicated. The baseline probability of UTI in circumcised boys is less than 1%, and testing is indicated only when at least three of these symptoms are present.

Urine microscopy and dipstick testing for leukocyte esterase, nitrites, or blood are useful to rule out UTI. A positive result supports empiric antibiotic treatment, but a urine culture should be obtained to confirm the diagnosis.

To diagnose UTI in a symptomatic child, urine testing must show pyuria and the culture must show significant bacterial growth. Urine specimens should be collected using techniques that minimize contamination, such as suprapubic aspiration, bladder catheterization, or midstream clean catch. Perineal bagging is not acceptable when the risk of UTI is high and empiric therapy will be initiated.

The diagnosis of UTI requires findings of both pyuria (i.e., positive leukocyte esterase on dipstick urinalysis or white blood cells on urine microscopy) and significant bacterial growth on urine culture. The recommended techniques for urine collection and the minimum uropathogen count required for diagnosis vary by guideline (Table 1).2,10,11 The AAP recommends urine collection by suprapubic aspiration or bladder catheterization in febrile infants, and it requires at least 50,000 colony-forming units of uropathogen per mL of urine.10,11 The European Society of Pediatric Urology (ESPU) criteria also require pyuria and bacterial growth, but midstream clean catch is acceptable in toilet-trained children, and the uropathogen criteria are lower than the AAP's.2

Urine specimens obtained via perineal bagging have an unacceptably high false-positive culture rate, which the AAP estimates ranges from 88% to 99%.10,11 For this reason, bagged specimens are useful only when dipstick urinalysis, microscopy, and culture results are all negative. Thus, these specimens are useful for ruling out UTI, but not for diagnosis.

Prompt antibiotic treatment is important to reduce the risk of renal scarring in children with UTIs. Initial antibiotic selection is based on local sensitivity patterns and the risk of resistant bacteria. Once available, culture results should be used to adjust the initial antibiotic selection. Pyelonephritis (i.e., febrile UTI) does not necessitate intravenous antibiotics; the route of administration should be based on the severity of illness, presence of renal abnormalities, response to therapy, and the child's age and ability to take oral medications. When intravenous antibiotics are used, a shorter course with transition to an oral agent is as effective as a longer intravenous regimen. Children with cystitis (i.e., afebrile UTI) should receive antibiotics for two to four days, whereas those with pyelonephritis should receive a seven- to 14-day course.

A 2014 Cochrane review found that oral antibiotics alone are as effective as a regimen of intravenous followed by oral antibiotics in children with pyelonephritis.21 It also found that shorter courses (two to four days) of intravenous antibiotics followed by transition to an oral regimen are as effective as longer courses of an intravenous agent. There were not enough data to apply these findings to infants younger than one month or to children with grades III to V vesicoureteral reflux. The ESPU recommends intravenous therapy for infants younger than two months because of increased rates of bacteremia and severe pyelonephritis.2 A 2019 study found no difference in the rates of recurrent UTI or hospital readmittance in infants younger than 60 days who received short (up to seven days) vs. longer courses of intravenous antibiotics for UTI and bacteremia.22 Thus, shorter courses of intravenous antibiotics followed by oral therapy can be considered for infants younger than 60 days.

A 2003 Cochrane review (with reaffirmation in 2010) found that two- to four-day courses of antibiotics are as effective as seven- to 14-day courses in children with cystitis.27 Although there are no data to support a specific duration of therapy in children with pyelonephritis, the AAP recommends seven to 14 days.10,11

Kidney and bladder ultrasonography is indicated for children with atypical UTIs to identify acute complications. Children with pyelonephritis who are 24 months or younger should undergo ultrasonography within six months of the acute infection. Ultrasonography should be performed in children older than 24 months who have recurrent UTIs. Voiding cystourethrography is also indicated for children with recurrent UTIs and for those with abnormal ultrasound findings. Dimercaptosuccinic acid (DMSA) imaging is not part of standard screening in the United States.

Voiding cystourethrography exposes children to radiation, and its value for detecting vesicoureteral reflux in patients with uncomplicated UTIs is questionable.10,11 Therefore, this imaging modality is reserved for children whose ultrasound findings suggest vesicoureteral reflux or obstructive uropathy, and for those with recurrent UTIs.10,11,23 Although British guidelines incorporate DMSA imaging to detect renal parenchymal defects, the AAP recommends against this modality except for research purposes.10,23

Antibiotic prophylaxis has been used to prevent recurrent UTIs and renal scarring. However, its benefit is unclear, and it promotes antimicrobial resistance. Patients most likely to benefit from antibiotic prophylaxis include children with a high risk of recurrent UTIs and those most likely to have adverse effects from recurrent UTIs. Nitrofurantoin is the preferred antibiotic for prophylaxis unless adverse effects limit its use. Bowel and bladder dysfunction (lower urinary tract symptoms concurrent with constipation) is associated with UTIs, and treatment of this condition can reduce UTI recurrence. Evidence does not support the use of probiotics or cranberries for UTI prophylaxis.

Evidence is mixed on the role of antibiotic prophylaxis to prevent recurrent UTIs. A Cochrane review and a systematic review suggest that long-term use of prophylactic antibiotics may reduce UTI recurrence; however, the benefit is small at best.6,7 The Randomized Intervention for Children with Vesicoureteral Reflux (RIVUR) trial showed that antibiotic prophylaxis reduced recurrent UTIs in children with grades I to IV reflux.8 However, a Cochrane review showed little to no effect on rates of recurrent UTIs.9

There is also conflicting evidence that antibiotic prophylaxis reduces renal scarring in children with recurrent UTIs. A Cochrane review found that antibiotic prophylaxis has little to no effect on the risk of new or progressive renal damage.9 The RIVUR trial also found no difference in renal scarring when antibiotic prophylaxis was used8; however, a systematic review and subanalysis of the RIVUR trial showed that antibiotic prophylaxis prevented scarring.7,28

Rates of recurrent UTIs can be as high as 51% in children with bowel and bladder dysfunction.29,30 Guidelines from the AAP and the ESPU emphasize the significance of bowel and bladder dysfunction as a risk factor for UTIs and the importance of treating this condition to prevent recurrent UTIs.2,11

Northern California Pediatric Hospital Medicine Consortium. Consensus guidelines for management of pediatric urinary tract infection (UTI). Updated April 2018. Accessed April 21, 2020. -tract-infection-full-guideline.pdf

Wang HH, Kurtz M, Logvinenko T, et al. Why does prevention of recurrent urinary tract infection not result in less renal scarring? A deeper dive into the RIVUR Trial. J Urol. 2019;202(2):400-405.

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