How is urine collected and analyzed in pediatric urinary tract infection (UTI)?

Updated: Mar 19, 2019
  • Author: Donna J Fisher, MD; Chief Editor: Russell W Steele, MD  more...
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Answer

The criterion standard for obtaining urine specimens for culture in pediatric patients is suprapubic aspiration. [32] However, catheterization is the most commonly used technique in infants and younger children. Midstream clean-catch urine specimens are adequate for older children who can provide them. The presence of at least 50,000 CFU/mL of a uropathogen is the AAP definition for a UTI. [3]

Culture of a urine specimen from a sterile bag attached to the perineal area has a false-positive rate so high that this method of urine collection is not suitable for diagnosing UTI. However, a culture of a urine specimen from a sterile bag that shows no growth is strong evidence that UTI is absent. [3]

Along with a positive urine culture, urinalysis showing pyuria and/or bacteriuria is part of the criterion standard for the diagnosis of UTIs. [3] Positive dipstick readings for nitrite, leukocyte esterase, or blood may also suggest a UTI. Dipstick tests have sensitivities of approximately 85-90%. Microscopic examination of spun urine can evaluate for the presence of white blood cells (WBCs), red blood cells (RBCs), bacteria, casts, and skin contamination (eg, epithelial cells).

On a suprapubic aspirate, the presence of 5 or more WBCs per high-power field suggests an infection. The presence of 10 or more WBC/μL is also consistent with infection. [33, 34] Gram stain of unspun urine may reveal organisms. A hemacytometer measures cells per volume and has been found to be more sensitive and specific than standard microscopic examination. [33, 34] The combination of hemacytometer cell count and Gram stain has been shown in studies to have a sensitivity approaching 95%.

Approximately 10-20% of pediatric patients with UTIs have normal urinalysis results. Multiple organisms may be present in patients with structural abnormalities.

A study by Tzimenatos et al that included an analysis of data from 4147 febrile infants ≤60 days old reported that for the 289 infants with a UTI and colony counts ≥50 000 CFUs/mL, a positive urinalysis regardless of bacteremia showed sensitivities of 0.94; 1.00 with bacteremia; and 0.94 without bacteremia. Specificity in all groups was 0.91. [63]

Methods of urine collection and examination, as well as salient findings, are shown in Tables 1 and 2, below.

Table 1. Urinalysis for Presumptive Diagnosis of Urinary Tract Infection* (Open Table in a new window)

Method

Findings

Bright-field or phase-contrast microscopy of centrifuged urinary sediment

Bacteria

Gram stain of uncentrifuged or centrifuged urinary sediment

Bacteria

Nitrite and leukocyte esterase test

Positive = UTI likely

Nitrite test

Positive = UTI probable

Leukocyte esterase test

Positive = UTI probable

*Negative microscopic findings for bacteria do not rule out a UTI, nor do negative results of dipstick testing for nitrite and leukocyte esterase. False-negative nitrite readings are especially common in children.

Table 2. Quantitative Urine Culture for the Diagnosis of Urinary Tract Infection* (Open Table in a new window)

Method

Finding

Suprapubic aspiration

If a UTI is present, bacteria are likely to be proliferating in bladder urine with growth of any organism except 2000-3000 CFU/mL coagulase-negative staphylococci.

Catheterization in a girl or midstream, clean-void collection in a circumcised boy

Febrile infants and children with UTI usually have >50,000 CFU/mL of a single urinary pathogen; however, UTI may be present with 10,000-50,000 CFU/mL of a single organism.*

Midstream, clean-void collection in a girl or uncircumcised boy

UTI is indicated when >100,000 CFU/mL of a single urinary pathogen is present in a symptomatic patient. Pyuria usually present. A UTI may be present with 10,000-50,000 CFU/mL of a single bacterium.*

Any method in a girl or boy

If the patient is asymptomatic, bacterial growth is usually >100,000 CFU/mL of the same organism on different days. If pyuria is absent, this result probably indicates colonization rather than infection.

*Patients with urinary frequency (ie, decreased bladder incubation time) are those most likely to have bacteria proliferating in the urinary bladder in the presence of low colony counts.


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