A wet mount test (wet prep) is a rapid diagnostic procedure used in a clinical setting to examine a sample of vaginal discharge under a microscope. This test is a frontline tool for investigating symptoms like itching, burning, unusual odor, or abnormal discharge. Its primary purpose is to identify the cause of vaginitis, which is inflammation of the vagina and vulva. Elevated white blood cells (leukocytes) in the sample strongly indicate an inflammatory or infectious process in the lower genital tract. This finding guides the clinician toward further investigation but does not pinpoint a specific cause.
Understanding White Blood Cells and the Wet Mount Test
White blood cells are the immune system’s first responders, migrating to any site of tissue injury or microbial invasion. When a pathogen or irritant disrupts the vaginal environment, these leukocytes travel to the area to neutralize the threat, causing a localized inflammatory response. A small number of white blood cells is a normal physiological finding, especially during menstruation or ovulation. However, a count exceeding the normal threshold signals a problem and prompts a closer look at potential causes.
Clinicians quantify this presence by counting the number of leukocytes per high-power field (WBCs/hpf) under magnification. Generally, a count greater than 10 WBCs per hpf is considered elevated, suggesting significant inflammation or infection. Some clinicians also use a ratio of white blood cells to epithelial cells, where a ratio greater than 1:1 suggests inflammation. The wet mount test establishes inflammation, which helps differentiate between infectious and non-infectious causes.
Infectious Causes Often Identified Directly by Wet Mount
Several common infections causing inflammation and elevated white blood cells can be diagnosed or strongly suspected directly from the wet mount. The parasitic infection Trichomoniasis is a frequent cause of a high leukocyte count, often exceeding 10 WBCs per hpf. The motile, pear-shaped Trichomonas vaginalis parasites are often visible, characterized by their jerky movement, providing a definitive diagnosis alongside inflammatory markers.
Vaginal candidiasis (yeast infection) also causes an inflammatory response, leading to a mild to moderate increase in leukocytes. The hallmark finding is the microscopic identification of Candida species, typically appearing as hyphae (branching filaments) or budding yeast spores.
Bacterial Vaginosis (BV) is an imbalance in the vaginal flora rather than a true inflammatory infection, and typically does not cause a significant elevation in white blood cells. Although the wet mount is a primary diagnostic tool for BV, the key visual clue is the presence of “clue cells”—vaginal epithelial cells covered in adherent coccobacilli. If a high white blood cell count is observed alongside clue cells, it suggests a co-existing condition, such as cervicitis or another infection, since BV itself is often non-inflammatory.
Secondary and Systemic Infections Requiring Further Testing
Elevated white blood cells on a wet mount can also indirectly indicate infections originating in the cervix or upper reproductive tract, which require specialized testing. Infections like Chlamydia and Gonorrhea primarily target the cervix, causing cervicitis (inflammation of the cervical tissue). The white blood cells seen in the vaginal discharge often migrate down from the inflamed cervix.
Although an elevated WBC count (sometimes exceeding 30 cells per hpf) is associated with a higher likelihood of these sexually transmitted infections, the wet mount alone is not sensitive or specific enough for a definitive diagnosis. Specialized laboratory techniques, such as Nucleic Acid Amplification Tests (NAAT), are required to accurately detect the DNA of Chlamydia trachomatis and Neisseria gonorrhoeae. The presence of leukocytes serves as an alert that further, targeted testing is necessary to rule out these serious pathogens.
A significant elevation of white blood cells can also point toward Pelvic Inflammatory Disease (PID), an infection that has ascended into the uterus, fallopian tubes, or ovaries. Inflammation found on the wet mount, especially in women with risk factors or pelvic pain, supports the need for a PID diagnosis. Non-infectious causes, such as chemical vaginitis from irritants like douches, soaps, or spermicides, can also cause a mild increase in leukocytes.
How Clinicians Determine the Cause and Treatment
The high white blood cell count found on a wet mount is rarely interpreted in isolation; it is integrated into a larger diagnostic picture. Clinicians use differential diagnosis, combining the WBC finding with other in-office examination results to narrow down potential causes. A simple pH test is performed: an elevated pH (usually above 4.5) is characteristic of Trichomoniasis and Bacterial Vaginosis, while a normal acidic pH suggests a yeast infection.
The “whiff test” is also performed, where discharge is mixed with a potassium hydroxide (KOH) solution to check for a strong, fishy odor. This odor points toward amine compounds produced by anaerobic bacteria associated with BV and sometimes Trichomoniasis. By combining the WBC count, pH level, whiff test results, and the presence of organisms like Trichomonas or yeast, a provider can quickly establish a presumptive diagnosis. Treatment typically involves antibiotics for bacterial or parasitic infections, or antifungals for yeast overgrowth. For suspected upper tract infections, such as those indicated by persistent cervicitis, samples are sent for accurate NAAT testing before prescribing systemic therapy.