Often, it seems as if the quest for “an answer” can cause us to see what is not there.  This is particularly problematic with respect to the quest to decipher the cause of fever.  Appropriately, we may consider the potential for a Urinary Tract Infection (UTI) as the source of the fever.  We have previously discussed how the duration of fever can influence the likelihood of finding a UTI as well as how finding a UTI can diminish the likelihood of there being meningitis.  The question, though is whether we are making the correct diagnosis. Let us take a minute to review the Diagnosis of UTI.

UTI: Basics

• UTI is the 2nd most common bacterial infection, following AOM.
• UTI is the most common serious bacterial infection in febrile infants/children.
  • 10% of all febrile children
  • 7% of febrile new-borns with high rates of concurrent bacteremia
  • Uncircumcised male infants < 3 months of age and females < 12 months have the highest prevalence of UTI
• UTI can become a big problem in children!
  • Pyelonephritis
  • Chronic UTIs
  • Renal scarring (still being debated) [Becknell, 2015]
  • Chronic renal insufficiency
  • Hypertension
  • Urosepsis

UTI: Presentation

• Unfortunately, the classic presentation (dysuria, frequency, and hesitancy) is not reliably found in children.
• Children often present with non-specific symptoms (just because they like to be difficult).
  • Infants may have vomiting, unexplained fever, failure to thrive, irritability, lethargy or jaundice.
  • Older children who can communicate better may complain of dysuria, but may also report non-specific abdominal pain and/or vomiting.
  • Older children may also present with hematuria or even incontinence / enuresis.

UTI: Making the Diagnosis

• As with any diagnosis, you first need to consider the probability of it existing in an individual patient.
• Weighing Risk Factors can be helpful in doing this. [Roberts, 2011]
  • Girls:
    • Characteristics:
      • White race
      • Age < 12 months
      • Fever for 2 or more days
      • Temperature of 39 C (102.2F) or higher
      • Absence of other source of infection
    • If 0 or 1 characteristic – probability of UTI is </= 1%
    • If 2 characteristics – probability of UTI is </= 2%
  • Boys:
    • Characteristics:
      • Non-Black race
      • Fever for 24 hours or greater
      • Temperature of 39C (102.2F) or higher
    • If Uncircumcised, probability of UTI is > 1%.
    • If Circumcised and 0-2 characteristics – probability of UTI is </= 1%
    • If Circumcised and 3 characteristics – probability of UTI is </= 2%

• AAP Practice Guideline states that a diagnosis of UTI requires BOTH: [Roberts, 2011]
  • Pyuria and/or Bacteriuria on urinalysis AND
  • >50,000 colony forming units/mL of a single uropathogen on urine culture.
    • Bagged urine samples CANNOT be used to make the diagnosis! [Roberts, 2011]
    • This means that without culture results, we can, at best, only make a presumptive diagnosis of UTI.
    • Additionally, this also means that a Urine Culture result with >50,000 CFUs/mL does not necessarily equate to a UTI either. If no pyuria, it is asymptomatic bacteriuria.

• Other test considerations:
  • Point of Care Urinalysis may have more rapid turn-around times, but it has lower sensitivities compared to a laboratory performed U/A. [Kazi, 2013]
  • Urinalysis is NOT a substitute for urine culture.
    • Nitrites:
      • Low sensitivity
        • Not all pathogens convert nitrate to nitrite. (False negative)
        • It takes at least 4 hours for conversion to happen. (False negative)
      • High specificity, though, as there are few False positives.
    • Leukocyte Esterase:
      • Some have found it to be very sensitive. [Schroeder, 2015]
      • Has 20% False negative rate. (High urine flow rate can prevent LE from accumulating).
      • Has numerous causes of False positives (ex, Strep infection, Kawasaki’s Disease).
  • Urine Microscopy
    • Pyuria alone does not constitute UTI.
    • Normal Urine WBC count < 5 /hpf
    • Presence of bacteria in unspun sample correlates with 10×5 CFUs/mL on culture.

Moral of the Morsel

• Be mindful not to satisfy your desire to have an “answer” by equating LE+ on U/A with a UTI.
• Acknowledge the fact that we can only make a presumptive diagnosis of UTI without the culture result.
  • If the patient is at higher risk for UTI:
    • It may be appropriate to treat with antibiotics empirically.
    • Discuss with the family the need to have the culture results reviewed to make the definitive diagnosis (and either continue therapy or stop it).
  • If the patient is at lower risk for UTI:
    • Discuss taking a watchful waiting approach. [Newman, 2013]
    • Having the culture results will help avoid unnecessarily and potentially harmful antibiotic exposure.

References