Leukocytes, commonly known as white blood cells (WBCs), are components of the immune system designed to detect and neutralize threats like bacteria or viruses. When a urinalysis detects these cells, it signals that the body’s immune response is active somewhere along the urinary tract. A finding of 75 leukocytes per high-power field (hpf) represents a significant elevation, strongly indicating the presence of inflammation or an ongoing infection. This high concentration means the body is actively mobilizing its defenses to fight a pathogen within the kidneys, ureters, bladder, or urethra.
What Leukocytes Are and Normal Levels
Leukocytes are the body’s cellular defense force, primarily produced in the bone marrow, and their function is to protect the body from foreign invaders. In a healthy individual, the urinary tract is considered sterile, meaning that urine should contain very few, if any, of these immune cells. A routine microscopic examination of urine sediment under a high-power field typically shows a normal count of zero to five white blood cells per hpf.
The term used to describe an elevated concentration of white blood cells in the urine is pyuria, which translates to pus in the urine. Pyuria is generally defined as a count exceeding 10 WBCs per hpf. The reported count of 75 leukocytes per hpf is substantially higher than the normal threshold, confirming a significant inflammatory response. This high number suggests a substantial immunological reaction is occurring, which requires medical investigation to pinpoint the exact source of irritation.
The Most Common Causes of a High Count
The most frequent cause for a leukocyte count of 75/hpf is a bacterial infection within the urinary system, specifically a Urinary Tract Infection (UTI). In a lower UTI, bacteria like Escherichia coli (E. coli) colonize the urethra or bladder (cystitis), prompting a localized influx of leukocytes to combat the proliferation of pathogens. The presence of both leukocytes and nitrites in the urine often suggests a bacterial UTI, as nitrites are metabolic by-products of certain bacteria.
A more concerning cause for this high count is pyelonephritis, which is a kidney infection that can develop if a lower UTI travels upward. This upper tract infection is more severe, triggering a pronounced immune response that releases a larger number of leukocytes into the urine. Other infectious agents, such as those responsible for sexually transmitted infections (STIs) like Chlamydia trachomatis and Neisseria gonorrhoeae, can also cause significant pyuria. These pathogens, however, may not always show up on a standard bacterial culture, leading to a condition known as sterile pyuria.
Non-infectious causes can also lead to a leukocyte count of 75/hpf, often by creating physical irritation or inflammation within the urinary structures. Kidney stones, for instance, can cause trauma and inflammation as they pass or become lodged, leading to a high white blood cell count. Certain systemic conditions, such as autoimmune disorders like lupus, or drug-induced inflammation of the kidney tissue, known as interstitial nephritis, can also cause pyuria. In women, a high count can sometimes result from external contamination of the urine sample by vaginal inflammation or discharge, which is why a clean-catch midstream sample is always recommended.
Confirming the Diagnosis and Treatment
A finding of 75 leukocytes/hpf requires prompt diagnostic steps to determine the underlying cause and guide appropriate treatment. The initial urinalysis is typically followed by a urine culture. This test isolates and identifies the specific type of bacteria or fungus present in the urine sample, which is essential if an infection is suspected.
The culture also determines the antibiotic sensitivity of any identified bacteria, ensuring the prescribed medication will be effective against the pathogen. If the culture is negative despite the high leukocyte count (sterile pyuria), further testing may be warranted to look for less common pathogens like those causing STIs or tuberculosis. Imaging studies, such as an ultrasound or CT scan, may be used to visualize the urinary tract if kidney stones or structural issues are suspected.
Treatment is entirely dependent on the confirmed diagnosis. For a confirmed bacterial UTI, a course of antibiotics is the standard treatment to eradicate the infection. If the cause is non-infectious, such as kidney stones, treatment may involve pain management, increased fluid intake, or procedures to remove the stones. Ignoring a significantly elevated leukocyte count is ill-advised, as it can indicate an infection that may progress to serious conditions like sepsis or chronic kidney damage if left untreated.