Leukocyte esterase

Leukocyte Esterase

Leukocyte esterase is an enzyme found in most white blood cells (leukocytes). It is commonly used as a marker in urinalysis to detect the presence of white blood cells in the urine, which can indicate a urinary tract infection (UTI) or other inflammatory conditions.

Biochemistry

Leukocyte esterase is an enzyme that catalyzes the hydrolysis of esters. It is produced by neutrophils, a type of white blood cell that plays a crucial role in the body's immune response. When neutrophils are present in the urine, they release leukocyte esterase, which can be detected using specific chemical tests.

Clinical Significance

The presence of leukocyte esterase in urine is a common indicator of inflammation or infection in the urinary tract. A positive leukocyte esterase test suggests pyuria, which is the presence of white blood cells in the urine. This can be associated with conditions such as:

• Urinary tract infection (UTI)
• Pyelonephritis
• Cystitis
• Interstitial nephritis

The leukocyte esterase test is often used in conjunction with other tests, such as the nitrite test, to diagnose UTIs. A positive result for both leukocyte esterase and nitrites is highly suggestive of a bacterial infection.

Testing Method

Leukocyte esterase is typically detected using a dipstick test during a routine urinalysis. The dipstick contains a reagent that changes color in the presence of leukocyte esterase. The intensity of the color change is proportional to the amount of enzyme present, allowing for a semi-quantitative assessment.

Procedure

1. A urine sample is collected from the patient. 2. A dipstick is immersed in the urine sample. 3. The dipstick is removed and excess urine is blotted off. 4. After a specified time, the color change on the dipstick is compared to a color chart to determine the presence and concentration of leukocyte esterase.

Interpretation of Results

• Negative: No color change, indicating the absence of leukocyte esterase.
• Trace: Slight color change, indicating a small amount of leukocyte esterase.
• Positive: Significant color change, indicating the presence of leukocyte esterase and suggesting pyuria.

A positive leukocyte esterase test should be interpreted in the context of the patient's symptoms and other laboratory findings. Further diagnostic testing, such as urine culture, may be necessary to confirm the presence of an infection and identify the causative organism.

Limitations

While the leukocyte esterase test is a useful screening tool, it has limitations. False positives can occur due to contamination of the urine sample or the presence of other substances that interfere with the test. False negatives may occur if the urine is very dilute or if the patient has a low white blood cell count.

Also see

• Urinalysis
• White blood cell
• Neutrophil
• Urinary tract infection
• Pyuria