What is the significance of a positive White Blood Cell (WBC) esterase test and a negative urine culture in a 5-year-old female?

From the Guidelines

In a 5-year-old female with positive WBC esterase but negative urine culture, this likely represents asymptomatic pyuria which generally does not require antibiotic treatment. The presence of white blood cell esterase indicates inflammation in the urinary tract, but without bacterial growth on culture, this is not a confirmed urinary tract infection 1. If the child has no symptoms (fever, pain with urination, frequency, urgency), observation is appropriate. Ensure adequate hydration and encourage regular, complete voiding.

Key Considerations

• The leukocyte esterase test has higher sensitivity but lower specificity for urinary tract infection compared to the nitrite test 1.
• A meta-analysis found that the presence of either nitrite or leukocyte esterase on a urine dipstick has a sensitivity of 88% and a false positive rate of 7% for urinary tract infection 1.
• The American Academy of Pediatrics recommends that if the urinalysis results are negative, it is reasonable to monitor the clinical course without initiating antimicrobial therapy, recognizing that negative urinalysis results do not rule out a UTI with certainty 1.

Management

• If symptoms are present, consider a repeat urinalysis and culture before starting antibiotics.
• Common causes of sterile pyuria include partially treated UTI, viral infection, kidney stones, or contamination during collection.
• If this finding persists on multiple tests or if the child develops symptoms, further evaluation may be warranted, including imaging studies like renal ultrasound to rule out anatomical abnormalities.
• In recurrent cases, consultation with pediatric nephrology or urology might be necessary to investigate underlying conditions that could predispose to urinary tract inflammation.

From the Research

Urine Test Results

• A 5-year-old female with a negative urine culture and positive WBC esterase result may indicate the presence of a urinary tract infection (UTI) that is not detected by the culture 2.
• The presence of leukocyte esterase in the urine is a marker of inflammation and can be an indicator of a UTI, even if the culture is negative 3, 4.
• A study found that a positive leukocyte esterase test had a likelihood ratio of 2.5 for predicting E. coli versus non-E. coli infections 2.

Interpretation of Results

• The results of the urine test should be interpreted in the context of the patient's symptoms and medical history 3.
• A negative urine culture does not necessarily rule out a UTI, as some infections may not be detected by culture 2, 4.
• The use of automated urinalysis and urine test strip readers can provide more accurate and reliable results than manual microscopy 3, 5.

Clinical Implications

• The presence of WBC esterase in the urine, even with a negative culture, may indicate the need for further evaluation and treatment of a UTI 2.
• The choice of antibiotic treatment may depend on the predicted causative agent of the UTI, with E. coli infections being more common in patients with positive UA results 2.
• Clinicians should be aware of the limitations of urine testing and consider other diagnostic tools and clinical factors when evaluating patients with suspected UTIs 3, 4.