When a routine urinalysis reveals the presence of leukocytes, or white blood cells, in the urine, it signals that the body’s immune system has been activated within the urinary tract. This finding is a direct indicator of inflammation or irritation somewhere along the path from the kidneys to the urethra. Understanding this result is a necessary step toward identifying the underlying cause, which can range from a common infection to a less frequent systemic condition. The presence of these cells requires further investigation for accurate interpretation and appropriate medical attention.
Understanding White Blood Cells
Leukocytes are immune cells produced in the bone marrow, circulating throughout the body in the blood and lymphatic tissues. Their primary responsibility is to protect the body against foreign invaders, such as bacteria, viruses, and other entities that pose a threat to health. Upon detecting a problem, they exit the bloodstream through a process called emigration to reach the site of concern.
These cells are the mobile defense units of the immune system, designed to engulf and destroy harmful microorganisms and clear away cellular debris. A healthy urinary tract allows very few of these cells to pass into the urine, as they are typically reabsorbed or not present in significant numbers. When inflammation is present, a large-scale mobilization of these cells occurs, leading to their elevated presence in the urine.
Defining Leukocyturia
Leukocyturia is the clinical term used to describe an abnormally high number of leukocytes found in a urine sample. While a small number of white blood cells is considered normal due to the natural shedding of cells, the accepted threshold for a positive finding is typically above 5 white blood cells per high-power field (WBCs/HPF) in a microscopic examination. The detection of the enzyme leukocyte esterase on a urine dipstick test is a rapid chemical indicator that suggests leukocyturia is present.
A specific diagnostic challenge arises with a condition known as sterile pyuria, which is characterized by elevated leukocytes in the urine but a negative result on a standard urine culture. This finding indicates that the inflammation is not caused by common bacteria, but may instead point toward fastidious organisms like Chlamydia or Mycobacterium, or non-infectious causes. Identifying the presence of these cells is a strong sign of urinary tract irritation.
Common Reasons for Elevated Levels
The most frequent reason for an increased leukocyte count in urine is an infection, which triggers a direct inflammatory response in the urinary system. A Urinary Tract Infection (UTI) occurs when bacteria enter the urethra and multiply, often leading to cystitis (bladder infection). The body sends a flood of leukocytes, primarily neutrophils, to the infected area to fight the multiplying bacteria.
A more serious condition is pyelonephritis, a kidney infection that develops when a lower UTI spreads upward. The inflammation and subsequent leukocyte recruitment occur within the kidney tissue itself, leading to a much higher concentration of white blood cells in the urine. This process often involves systemic symptoms like fever and flank pain alongside urinary discomfort.
Non-infectious physical obstructions, such as kidney stones, can also result in significant leukocyturia. As a stone moves through the ureter or bladder, it causes mechanical irritation and tissue damage to the lining of the urinary tract. This irritation prompts an inflammatory response that draws leukocytes to the area, even without the presence of bacteria.
Other causes of sterile pyuria include sexually transmitted infections (STIs), such as gonorrhea and chlamydia, which cause inflammation in the urethra and genital tract. Inflammation of the prostate, known as prostatitis, or interstitial cystitis can also raise leukocyte levels without a typical bacterial infection. A poorly collected sample can lead to false positives if the urine becomes contaminated with white blood cells from the surrounding genital area, particularly in women.
Measuring Levels and Follow-Up Actions
The initial detection of leukocytes in urine is usually performed as part of a routine urinalysis using a chemical dipstick test for leukocyte esterase. A positive result prompts a microscopic examination of the urine sediment, which allows a healthcare provider to count the actual number of white blood cells per high-power field. This microscopic count provides a quantifiable measure of the severity of the inflammation.
Following a positive result, the necessary next step is often a urine culture, which is used to identify the specific type and quantity of bacteria present. If a bacterial infection is confirmed, treatment typically involves a course of targeted antibiotics to eliminate the pathogen. If the culture is negative, indicating sterile pyuria, further diagnostic tests are often necessary to pinpoint the non-bacterial cause.
These subsequent investigations may include specialized testing for atypical organisms like tuberculosis or STIs, or imaging studies such as an ultrasound or CT scan. Imaging is useful for detecting non-infectious causes, such as kidney stones or structural abnormalities that may be causing obstruction and inflammation. The specific treatment plan will be directed by the underlying cause, whether it involves antibiotics, anti-inflammatory medication, or procedures to remove a physical obstruction.