pediatrics
Urinary Tract Infection (UTI) in Children
Diagnosis of UTI in Children
Urine analysis and culture Often urinary tract imaging (See also the American Academy of Pediatrics'2011and2016practice guidelines for the diagnosis and management of the initial UTI in febrile infants and children 2 to 24 months.) A reliable diagnosis of urinary tract infection requires the presence of pyuria on urinalysis and positive bacterial culture in properly collected urine, before an antimicrobial is given. A diagnosis of probable UTI may be made by the presence of pyuria on urinalysis, while culture results are pending. Most clinicians obtain urine by transurethral catheterization in infants and young children, reserving suprapubic aspiration of the bladder for boys with moderate to severe phimosis. Both procedures require technical expertise, but catheterization is less invasive, slightly safer, and has sensitivity of 95% and specificity of 99% compared with suprapubic aspiration. Bagged specimens are unreliable and should not be used for diagnosis. Urine cultureresults are interpreted based on colony counts. If urine is obtained by catheterization or suprapubic aspiration,≥5×104colonies/mL commonly defines UTI. Clean-catch, midstream-voided specimens are significant when colony counts of a single pathogen (ie, not the total count of mixed flora) are≥105colonies/mL. However, at times symptomatic children may have UTI despite lower colony counts on urine cultures. Urine should be examined by urinalysis and cultured as soon as possible or stored at 4°C if a delay of>10 minutes is expected. Occasionally, UTI may be present despite colony counts lower than the described guidelines, possibly because of prior antibiotic therapy, very dilute urine (specific gravity<1.003), or obstruction to the flow of grossly infected urine. Sterile cultures generally rule out UTI unless the child is receiving antibiotics or the urine is contaminated with antibacterial skin-cleaning agents. Microscopic examinationof urine is very useful but not definitive. Pyuria (>5 white blood cells (WBCs)/high-power field in spun urine sediment) is about 96% sensitive for UTI and 91% specific. Raising the threshold of pyuria to > 10 WBCs/high-power field in spun urine sediment decreases the sensitivity to 81% but is more specific (97%). A WBC count (using a hemocytometer)>10/mcL (0.01 × 109/L) inunspunurine has greater sensitivity (90%) but is not used by many laboratories. Presence of bacteria on urinalysis of spun or unspun fresh urine is about 80 to 90% sensitive but only 66% specific; Gram stain of the urine to detect the presence of bacteria is about 80% sensitive and 80% specific. Dipstick testson urine to detect gram-negative bacteria (nitrite test) or WBC (leukocyte esterase test) are typically done together; if both are positive, the diagnostic sensitivity for UTI is about 93 to 97% and the specificity is about 72 to 93%. Sensitivity is lower for each individual test, especially for the nitrite test (about 50% sensitivity), because it may take several hours for bacterial metabolism to produce nitrites, and frequent voiding by children may preclude nitrite detection. The specificity of the nitrite test is quite high (about 98%); a positive result on a freshly voided specimen is highly predictive of UTI. Sensitivity of the leukocyte esterase test is 83 to 96% and specificity is 78 to 90%. In a recent multicenter analysis of infants with fever, the aggregate urinalysis findings of pyuria, positive leukocyte esterase, or presence of nitrites was 90 to 95% sensitive and 91% specific for UTI; in the study population, this yielded a positive predictive value of 40% and a negative predictive value of 100% ( Urine tests reference ). Differentiating an upper UTI from a lower UTI can be difficult. High fever, costovertebral angle tenderness, and gross pyuria with casts indicate pyelonephritis; an elevated C-reactive protein level also tends to be associated with pyelonephritis. However, many children without these symptoms and signs have an upper UTI. Tests to distinguish upper infection from lower infection are not indicated in most clinical settings because treatment is not altered. 1.Tzimenatos L, Mahajan P, Dayan PS, et al: Accuracy of the urinalysis for urinary tract infections in febrile infants 60 days and younger.Pediatrics141(2):e20173068, 2018. doi: 10.1542/peds.2017-3068 A complete blood count and tests for inflammation (eg, erythrocyte sedimentation rate, C-reactive protein) may help diagnose infection in children with borderline urine findings. Some authorities measure serum bloodureanitrogen and creatinine during a first UTI. Blood cultures are appropriate for infants with UTIs and for children>1 to 2 years who appear toxic. Many major renal or urologic anomalies now are diagnosed in utero by routine prenatal ultrasonography, but a normal result does not completely exclude the possibility of anatomic anomalies. Thus, renal and bladder ultrasound imaging is typically done in children < 3 years of age after their first febrile urinary tract infection. Some clinicians do imaging on children up to 7 years of age or older. Renal and bladder ultrasonographyhelps exclude obstruction and hydronephrosis in children with febrile UTIs and is typically done within a week of diagnosing UTI in infants. Ultrasonography is done within 48 hours if infants do not respond quickly to antimicrobials or if their illness is unusually severe. Beyond infancy, ultrasonography may be done in the few weeks after the UTI diagnosis. Voiding cystourethrography(VCUG) andradionuclide cystography(RNC) are better than ultrasonography for detecting vesicoureteral reflux and anatomic abnormalities and previously were recommended for most children after a first urinary tract infection. However, VCUG and RNC both involve use of radiation and are more uncomfortable than ultrasonography. Also, the role VUR plays in the development of chronic renal disease is undergoing reevaluation, making the immediate diagnosis of VUR less urgent. Thus, VCUG is no longer routinely recommended after the first UTI in children, especially if ultrasonography is normal and if children respond quickly to antibiotic therapy. VCUG is reserved for children with the following: Ultrasonographic abnormalities (eg, scarring, significant hydronephrosis, evidence of obstructive uropathy or suggestion of VUR) Complex UTI (ie, persistent high fever, organism other thanE. coli) Recurrent febrile UTIs If VCUG is to be done, it is done at the earliest convenient time after clinical response, typically toward the end of therapy, when bladder reactivity has resolved and urine sterility has been regained. If imaging is not scheduled until after therapy is due to be completed, children should continue antibiotics at prophylactic doses until VUR is excluded. Radionuclide scanning is now used mainly to detect evidence of renal scarring. It is done using technetium-99m-labeled dimercaptosuccinic acid (DMSA), which images the renal parenchyma. DMSA scanning is not a routine test, but it may be done if children have risk factors such as abnormal ultrasound results, high fever, and organisms other thanE. coli. 