Correlation between cervical cytologic results and Gram stain as diagnostic tests for bacterial vaginosis

Our purpose was to determine the reliability of the Papanicolaou smear in making the diagnosis of bacterial vaginosis with the vaginal Gram stain used as the diagnostic standard.

We conducted a prospective, blinded, cross-sectional study of 210 consecutive patients referred to the Colposcopy Clinic for evaluation of abnormal cervical cytologic results. Each patient had a standard Papanicolaou smear and Gram stain of vaginal discharge. The sensitivity, specificity, positive predictive value, and negative predictive value of the Papanicolaou smear were determined with the Gram stain used as the standard for diagnosis of bacterial vaginosis.

Of the 210 patients, 80 (38.1%) had Gram stains that were positive for bacterial vaginosis and 118 (56.2%) had negative Gram stains. Twelve (5.7%) had intermediate Gram stains that were also considered negative. Of the 80 patients with positive Gram stains, 44 had cervical smears consistent with bacterial vaginosis and 36 had negative smears. Of the 130 patients with negative Gram stains, two had a positive cervical smear. Therefore, compared to the Gram stain, cervical cytologic test results had a sensitivity of 55% and a specificity of 98%. The respective positive predictive and negative predictive values were 96% and 78%.

Compared to Gram stain of vaginal secretions, the cervical Papanicolaou smear has fair sensitivity (55%) and excellent positive predictive value (96%) in diagnosing bacterial vaginosis.