LEU is the abbreviation for Leukocytes, which are the body’s white blood cells and a main component of the immune system. Their presence in the urine indicates that the body is activating its defenses against a potential threat. A positive LEU result commonly signals that the urinary tract is experiencing inflammation or is actively fighting an infection. This finding alerts a healthcare provider to the possibility of an underlying issue that requires further investigation.
Defining Leukocytes and Urinalysis
Leukocytes are immune cells produced in the bone marrow, designed to seek out and neutralize foreign invaders, such as bacteria, viruses, or fungi. They circulate throughout the body and are concentrated at sites of inflammation or infection to destroy pathogens and repair tissue. Under normal, healthy conditions, only a very small number of these cells, typically 0 to 5 white blood cells per high-powered field, pass into the urine.
The detection of these cells is a standard part of a urinalysis, a test performed to screen for various health conditions. Initial screening often uses a chemical dipstick test which looks for leukocyte esterase, an enzyme found within the white blood cells. A color change on the dipstick indicates a positive result, suggesting that a significant number of leukocytes are present in the sample. This chemical test is usually followed by a microscopic examination, where a lab technician visually counts the actual number of white blood cells to confirm the finding.
Common Reasons for Leukocytes in Urine
The most frequent reason for elevated leukocytes in the urine, a condition known as leukocyturia or pyuria, is a Urinary Tract Infection (UTI). A UTI occurs when bacteria, such as Escherichia coli, enter the urethra and multiply in the bladder or other parts of the urinary system. The immune system responds immediately by dispatching white blood cells to the site of infection to combat the invading bacteria.
If the infection progresses and moves up the urinary tract, it can lead to pyelonephritis, which is a more serious infection of the kidneys. Kidney infections generally cause a high concentration of leukocytes in the urine, often accompanied by symptoms such as fever, chills, and pain in the flank or back. Inflammation of the bladder lining, called cystitis, also causes a localized immune response that increases the number of white blood cells excreted.
Leukocyturia can also be caused by conditions other than standard bacterial UTIs:
- Sexually transmitted infections (STIs) like chlamydia or gonorrhea.
- Irritations from kidney stones, which cause physical trauma and inflammation as they pass, leading to a rise in leukocytes.
- Certain non-infectious inflammatory conditions, such as interstitial cystitis.
- The use of particular medications, which can also prompt this immune response.
Interpreting Results and Necessary Follow-Up
The LEU result is rarely interpreted in isolation; it is most informative when viewed alongside other markers on the urinalysis report. The primary correlating marker is Nitrite, which is produced when certain types of bacteria break down nitrate naturally present in the urine. A positive result for both Leukocytes and Nitrite is a strong indicator of an active bacterial infection.
Conversely, a positive LEU result with a negative Nitrite test suggests the presence of sterile pyuria, meaning the immune system is activated but a common bacterial cause is not detected. This finding points toward other potential causes, such as viral infections, tuberculosis, or non-infectious inflammation. In some cases, poor collection technique can introduce contamination from the genital area, leading to a false positive leukocyte reading.
Because a positive LEU result signifies an active process, confirmatory testing is often the next step. A urine culture is performed to identify the specific type of bacteria or other microorganism responsible for the infection and determine its sensitivity to different antibiotics. This step is necessary to ensure the correct treatment is prescribed and to avoid unnecessary antibiotic use. A healthcare provider must evaluate the full context of the test results, including the patient’s symptoms and medical history, to accurately diagnose the underlying cause.