Deciphering Leukocyte Esterase Test Outcomes

To decipher the outcomes of a leukocyte esterase test, here are the key points to consider:

Purpose and Method

The leukocyte esterase test is a screening tool used to detect the presence of white blood cells in the urine, which can indicate infection or inflammation in the urinary tract. The test is performed using a dipstick with a color-sensitive pad that changes color in the presence of leukocyte esterase, an enzyme produced by white blood cells234.

Interpreting Test Results

• Negative: No color change, indicating no detectable leukocyte esterase activity or white blood cells.
• Trace: A faint color change, suggesting minimal esterase activity, potentially from a mild or early-stage infection.
• Positive: A distinct color change, graded as:
  • Small ('+'): Low levels of leukocyte esterase.
  • Moderate ('++'): Moderate levels.
  • Large ('+++'): High levels4.

Color Indications

The color change on the dipstick corresponds to the level of leukocyte esterase present:

• Light brown or beige: Trace levels.
• Brown or shades of purple: Positive results, with deeper or darker colors indicating higher levels of leukocyte esterase24.

Normal Range

A normal range for leukocyte esterase in urine is typically under 5 white blood cells per high power field (WBC/HPF), reflected by a light color on the reagent pad indicating a negative result2.

Clinical Implications

• Positive Result: May indicate a urinary tract infection (UTI), kidney infection, or other inflammatory conditions. However, a positive result alone is not a definitive diagnosis, and further tests like urine culture may be necessary to confirm the presence and type of infection234.
• Negative Result: Suggests that an infection is unlikely, but does not completely rule out UTI, especially if symptoms persist. Additional tests may still be needed5.

Limitations and False Results

• False Positives: Can occur due to contamination with vaginal fluids, menstrual blood, hemoglobinuria, myoglobinuria, concentrated urine, strenuous exercise, and certain medications like imipenem and clavulanic acid14.
• False Negatives: Can occur due to elevated specific gravity (dehydration or kidney disease), elevated glucose or ketones in urine (uncontrolled diabetes, fasting, or low-carbohydrate diets), protein in urine (dehydration, intense exercise, or kidney disease), and the use of certain antibiotics like cephalexin, nitrofurantoin, and tetracycline4.

Factors Affecting Test Accuracy

• Medications: Certain antibiotics and other medications can influence the test results.
• Medical Conditions: Conditions like glomerulonephritis, elevated protein levels, and urinary tract infections can affect the accuracy.
• Sample Collection: Proper collection using a clean-catch method is crucial to avoid contamination and ensure accurate results234.

By understanding these aspects, healthcare providers can accurately interpret the results of the leukocyte esterase test and make informed decisions about further diagnostic steps and treatment.