What is the significance of white blood cells on a wet prep?

Significance of White Blood Cells on a Wet Prep

The presence of white blood cells (WBCs) on a vaginal wet preparation is a significant finding that indicates inflammation and suggests possible infection, particularly bacterial vaginosis, trichomoniasis, or pelvic inflammatory disease.

Diagnostic Significance

White blood cells on a wet prep serve as an important diagnostic marker for several conditions:

Pelvic Inflammatory Disease (PID)

• The presence of WBCs on saline microscopy of vaginal secretions is one of the additional criteria supporting a diagnosis of PID 1
• If cervical discharge appears normal and no white blood cells are found on wet prep, the diagnosis of PID is unlikely 1

Sexually Transmitted Infections (STIs)

• Elevated WBC counts (≥11 WBCs/HPF) are associated with increased odds of having gonorrhea, chlamydia, or trichomoniasis 2
• However, WBC counts alone have limited diagnostic utility, with sensitivity ranging from 48.2% to 53.9% and specificity from 67.2% to 68.8% 2
• Moderate to many WBCs on wet prep increase the probability of concurrent gonorrhea or chlamydia infection (odds ratio 1.58-2.47) 3

Bacterial Vaginosis and Vaginal Infections

• WBCs are evaluated as part of the wet mount preparation to diagnose vaginal infections 1
• The absence of WBCs with normal vaginal flora (abundant lactobacilli) is considered a normal finding 4

Interpretation Considerations

Several factors affect the interpretation of WBCs on wet prep:

Normal Variation

• Vaginal leucocytosis can occur once during each normal menstrual cycle in healthy asymptomatic women 5
• This normal physiological variation must be considered when evaluating wet smears for genital tract infections

Quantification and Thresholds

• Higher quantities of WBCs ("moderate" or "many") correlate better with STIs than lower counts 3
• For detection of chlamydial or gonococcal infection, >30 WBCs on vaginal wet mount has a likelihood ratio of 2.85 6

Diagnostic Context

• WBCs should be interpreted alongside other findings:
  • Vaginal pH (>4.5 suggests BV or trichomoniasis; ≤4.5 suggests candidiasis) 7
  • Presence of clue cells (bacterial-covered epithelial cells) for BV 1
  • Presence of trichomonads or yeast 1

Clinical Application

When performing a wet prep examination:

1. Collect vaginal secretions using a cotton swab
2. Place in 0.5 mL saline or transport swab 1
3. Examine within 2 hours for optimal results 1
4. Look for:
   • WBCs (quantify as none, few, moderate, many)
   • Clue cells
   • Moving trichomonads
   • Hyphae or budding yeast 1

Pitfalls and Caveats

• False positives: Normal physiological variation can cause increased WBCs during certain phases of the menstrual cycle 5
• Limited specificity: WBCs alone have modest specificity for STIs 2, 3
• Time sensitivity: Wet mount should be read as soon as the pelvic examination is completed to increase the likelihood of detecting trichomonads 1
• Clinical correlation: Always interpret WBCs in the context of other clinical findings and symptoms 1

In summary, while the presence of WBCs on wet prep is a valuable diagnostic indicator of inflammation and possible infection, it must be interpreted within the broader clinical context and alongside other laboratory findings to guide appropriate treatment decisions.