When a urine test mentions leukocytes, it indicates that white blood cells have been detected in the sample. Leukocytes are immune system cells that migrate to sites of inflammation or infection to fight off threats. Their presence in urine, known as pyuria, is a common finding during routine screenings or when investigating symptoms like painful urination. Testing for these cells is an initial step for healthcare providers to determine if an inflammatory process is occurring within the urinary tract.
What Leukocytes Are and Their Role in Urine
Leukocytes, commonly known as white blood cells, are the mobile defense units of the body’s immune system. These cells originate in the bone marrow and circulate throughout the body, constantly surveying for foreign invaders like bacteria, viruses, or fungi. The most prevalent type of leukocyte involved in fighting acute bacterial infections is the neutrophil, which actively engulfs and destroys pathogens.
When inflammation occurs along the urinary tract, these neutrophils are chemically signaled to leave the bloodstream. They migrate through the tissue walls and enter the urinary space to confront the source of the irritation. Normally, urine should contain very few white blood cells, typically fewer than five cells per high-power field when examined microscopically. A count significantly higher than this threshold indicates pyuria, demonstrating an active immune response is taking place.
How the Uristat Test Detects Leukocyte Esterase
The Uristat test and similar rapid dipstick methods do not directly count the white blood cells themselves. Instead, the test relies on detecting an enzyme called Leukocyte Esterase (LE), which is found almost exclusively inside the neutrophils. When these immune cells are present in the urine, they release LE, making the enzyme a reliable chemical marker for pyuria.
The test strip contains a small pad treated with chemicals that react specifically with the Leukocyte Esterase enzyme. This reaction triggers a subsequent chemical process, which results in a distinct color change on the pad. The intensity of this color change is proportional to the concentration of the enzyme in the urine sample.
Results from the LE test are semi-quantitative, meaning they provide an estimate rather than a precise count. The dipstick is read against a color chart, with results commonly reported as negative, trace, small (+), moderate (++), or large (+++). A positive result indicates the presence of white blood cells, suggesting inflammation, but it cannot differentiate between specific causes or quantify the exact number of cells present.
Primary Causes of Elevated Leukocytes in Urine
The most frequent reason for elevated leukocytes in the urine is a Urinary Tract Infection (UTI), typically caused by bacterial invasion of the urethra or bladder. The body launches an immediate defense, flooding the area with white blood cells to combat the multiplying bacteria. A positive leukocyte esterase result alongside a positive nitrite test strongly suggests a bacterial UTI.
A high leukocyte count can occur even without a common bacterial infection, a condition referred to as sterile pyuria. This can be caused by non-bacterial inflammation, such as interstitial cystitis, a chronic bladder condition. It can also be a sign of kidney infections, known as pyelonephritis, where the infection has ascended to the upper urinary tract.
Other causes include the movement of kidney stones, which causes irritation and inflammation within the urinary tract. Certain sexually transmitted infections, such as chlamydia or gonorrhea, can also cause inflammation of the urethra that results in pyuria. In women, contamination from vaginal discharge is a common non-pathological cause of a false positive result if a clean-catch sample technique was not used.
Follow-Up Diagnosis and Management
A positive leukocyte esterase result from a rapid test is considered a screening tool, not a definitive diagnosis, and requires further investigation. The next step is typically a microscopic urinalysis, where a lab technician examines a centrifuged urine sample under a microscope. This visual inspection confirms pyuria by counting the actual number of white blood cells, often reported as cells per high-power field.
If a significant number of leukocytes are confirmed, a urine culture and sensitivity test is usually performed to identify any specific bacteria present. The culture involves placing a small amount of the sample on a growth medium to see what microorganisms grow. Sensitivity testing then determines which antibiotics are most effective against the identified bacteria.
Management is directed at the underlying cause identified through these subsequent tests. For a confirmed bacterial infection, a course of targeted antibiotics will be prescribed to eliminate the pathogen. If the investigation reveals sterile pyuria, management shifts to treating non-infectious causes, such as addressing kidney stones or managing chronic inflammatory conditions.