Clinical Utility of Measuring White Blood Cells on Vaginal Wet Mount and Endocervical Gram Stain for the Prediction of Chlamydial and Gonococcal Infections

Background: White blood cells on endocervical Gram stain and vaginal wet mount are frequently used to predict chlamydial and gonococcal infections. Previous studies provide conflicting evidence for the clinical utility of these tests.

Goal: To evaluate the clinical utility of measuring white blood cells on vaginal wet mount and endocervical Gram stain for the prediction of chlamydial infection and gonorrhea.

Study Design: Women undergoing pelvic examinations at 10 county health department family planning and sexually transmitted disease clinics were tested for chlamydial infection by ligase chain reaction assay (n = 4550) and for gonorrhea by culture (n = 4402). Vaginal wet mount and endocervical Gram stains were performed in county laboratories at the time of examination.

Results: The prevalences of chlamydial infection and gonorrhea were 8.8% and 3.2%, respectively. For detection of chlamydial or gonococcal infection, the likelihood ratio was 2.85 (95% CI, 2.10-3.87) for > 30 white blood cells on vaginal wet mount and 2.91 (95% CI, 2.07-4.09) for > 30 white blood cells on endocervical Gram stain. Similar results were seen for individual diagnoses either of chlamydial infection or of gonorrhea.

Conclusion: Vaginal wet mount and endocervical Gram stain white blood cells are useful for the presumptive diagnosis of chlamydial infection or gonorrhea only in settings with a relatively high prevalence of infection or when other predictors can increase the likelihood of infection.