Bacterial Vaginosis (BV) is a common condition caused by an imbalance in the vaginal microbiome, where protective Lactobacilli are replaced by an overgrowth of other organisms. This shift frequently results in an unusual, thin, gray or white discharge with a distinct fishy odor. The presence of white blood cells in a urine sample, known as pyuria, suggests inflammation or infection in the genitourinary tract. Understanding the precise relationship between BV and pyuria is important for accurate diagnosis and effective treatment, preventing the misdiagnosis of a Urinary Tract Infection (UTI).
The Meaning of Leukocytes in Urine
Leukocytes are white blood cells, the primary component of the immune system, which fight off inflammation. When detected in urine, the condition is termed pyuria, signaling an active immune response within the genitourinary tract. Pyuria is generally defined by the presence of an elevated number of white blood cells per high-power field (hpf) under a microscope.
Pyuria is technically only a sign of inflammation, not definitive proof of a UTI. Leukocytes are often confirmed by a urine dipstick test that checks for leukocyte esterase, an enzyme found within these cells. A positive result warrants further microscopic examination. Results must be interpreted alongside a patient’s symptoms and other laboratory findings.
How Bacterial Vaginosis Can Influence Urine Tests
Bacterial Vaginosis does not infect the bladder or kidneys, but it can cause leukocytes in a urine test through contamination. The vagina and the external opening of the urethra are in close anatomical proximity. BV causes a significant increase in vaginal discharge, which contains white blood cells and cellular debris from inflammation.
During the standard “clean-catch” urine collection, this BV discharge can easily mix with the urine stream. The white blood cells from the discharge enter the collection cup, leading to a false-positive result for pyuria. This contamination is the most frequent reason a person with BV shows an elevated leukocyte count without having an actual UTI.
BV is also associated with an increased risk of developing a true UTI. The change in the vaginal environment, including the loss of protective Lactobacilli and the rise in pH, facilitates the colonization of uropathogens near the urethra. These uropathogens, such as Escherichia coli, can then ascend into the bladder to cause a genuine infection. Thus, BV can cause false pyuria through contamination while increasing the likelihood of a co-occurring true UTI.
Distinguishing Between Local Inflammation and True Urinary Tract Infection
Differentiating between pyuria caused by BV contamination and pyuria from a true UTI requires comparing symptoms and laboratory results. A true UTI typically presents with classic urinary symptoms such as painful urination, frequency, and urgency. In contrast, BV symptoms are primarily vaginal, including the characteristic fishy odor and thin, gray discharge.
A strict clean-catch technique is necessary to minimize cross-contamination and ensure sample quality. Laboratory testing, particularly urine culture and dipstick analysis, provides objective evidence. A true UTI is almost always characterized by significant bacteriuria—a high concentration of a single type of bacteria, such as E. coli, in the culture.
The dipstick offers a clue, as nitrites are highly suggestive of a true UTI. In simple BV contamination cases, the urine culture typically shows no significant bacterial growth or a mixed growth of non-uropathogenic bacteria. Pyuria without significant bacteriuria is termed “sterile pyuria,” pointing toward causes like vaginal contamination.
Treatment Pathways and Clinical Next Steps
The clinical next steps depend entirely on the confirmed diagnosis following laboratory tests and symptom evaluation. If the diagnosis is Bacterial Vaginosis alone, treatment focuses on restoring the vaginal flora balance using antibiotics such as metronidazole, prescribed as an oral tablet or a vaginal gel. Treating the BV resolves the vaginal inflammation and eliminates the source of contaminating white blood cells.
If the patient has both an active UTI and BV, both infections require specific and simultaneous treatment. The UTI is addressed with an appropriate antibiotic, such as nitrofurantoin or trimethoprim-sulfamethoxazole, tailored to the bacterium identified in the urine culture. Treating both conditions ensures a full recovery.
If the diagnosis remains unclear, or if contamination is suspected due to a polymicrobial culture or sterile pyuria, the provider may recommend a repeat urine test. This follow-up test must adhere strictly to the clean-catch protocol to obtain a reliable sample. Further evaluation, including a pelvic examination, may also be necessary to rule out other causes of inflammation contributing to leukocytes.