Leukocyte esterase (LE) is an enzyme produced by white blood cells, primarily neutrophils. Its presence in urine typically indicates an immune response within the urinary tract, often signaling inflammation or infection.
What Leukocyte Esterase Indicates
Leukocyte esterase in urine indicates the presence of white blood cells, which are usually fighting an infection or inflammation. The most common reason for finding leukocyte esterase is a urinary tract infection (UTI). UTIs are widespread infections that can affect various parts of the urinary system.
While UTIs are a primary cause, other conditions can also lead to the detection of leukocyte esterase in urine. These include kidney stones, which can cause irritation and inflammation. Additionally, inflammation within the urinary tract that is not caused by a bacterial infection, such as interstitial cystitis or certain kidney diseases, can also result in a positive leukocyte esterase test. The presence of leukocyte esterase simply points to the activity of white blood cells rather than directly identifying the specific cause of that activity.
How the Test is Performed
Testing for leukocyte esterase in urine is a straightforward and non-invasive procedure, typically conducted as part of a routine urinalysis. The process begins with collecting a urine sample, often using a “clean-catch” method to minimize contamination. This involves cleaning the genital area before urinating and collecting a midstream urine sample into a sterile container.
Once the urine sample is collected, a dipstick is used for the test. This dipstick is a narrow plastic strip embedded with chemical pads that react to specific substances in the urine. When the dipstick is immersed in the urine, the pad designed to detect leukocyte esterase changes color if the enzyme is present. The intensity of the color change provides an indication of the amount of leukocyte esterase in the sample.
Interpreting Test Results
A positive result indicates the presence of leukocyte esterase. This often prompts further investigation to determine the underlying cause, such as an infection or inflammation. Conversely, a negative result means no significant amount of leukocyte esterase was detected in the urine.
However, the leukocyte esterase test is a screening tool, not a definitive diagnosis, and can sometimes yield inaccurate results. False positives can occur due to contamination of the urine sample with vaginal secretions or certain medications. For instance, heavy menstrual discharge or a Trichomonas infection can introduce white blood cells into the sample, leading to a positive result even without a urinary tract infection.
False negatives are also possible, where the test fails to detect leukocyte esterase despite its presence. This can happen if the urine is very diluted, if there are high levels of protein or vitamin C in the urine, or if certain types of bacteria are present that do not trigger a strong leukocyte esterase response. Additionally, some types of white blood cells, like lymphocytes, may not produce a positive reaction on the dipstick test. Therefore, a single leukocyte esterase result is usually considered in conjunction with other clinical findings and tests.
Next Steps After a Positive Result
Following a positive leukocyte esterase result, healthcare providers typically recommend further diagnostic steps to confirm the cause of white blood cells in the urine. A common next step is a microscopic examination of the urine, also known as urinalysis with microscopy. This allows for direct visualization of white blood cells, red blood cells, bacteria, and other elements in the urine, providing a more detailed picture of the urinary tract’s condition.
Often, a urine culture is also performed to identify any specific bacteria present and determine their susceptibility to different antibiotics. This test involves growing bacteria from the urine sample in a laboratory to pinpoint the exact type of microorganism causing an infection. If a bacterial infection, such as a urinary tract infection, is confirmed, treatment usually involves prescribing antibiotics. It is important to consult a healthcare professional for proper diagnosis and treatment.