Comparison of Gram and Kopeloff stains in the diagnosis of bacterial vaginosis in pregnancy

Bacterial vaginosis (BV) is commonly diagnosed by using the Nugent score, a semiquantitative scoring system to evaluate bacterial morphotypes on Gram stain of vaginal secretions. Some authors have suggested using the Kopeloff modification of the Gram stain. Asymptomatic BV in pregnancy has been associated with adverse outcomes. We performed both stains on simultaneously collected vaginal smears from 2652 women at 24–26 weeks of gestation. Gram staining gave significantly higher (more abnormal) Nugent scores than Kopeloff staining. Compared to the Kopeloff stain, the number of specimens graded as indeterminate or consistent with BV by Gram stain increased by 29% (469 versus 364, P < .001). Interrater reliability of the Nugent score (n = 413) for Kopeloff staining was significantly better than Gram staining (agreement = 74% versus 63%, intraclass correlation coefficient = 0.87 versus 0.79, P < .05, 95% confidence intervals 0.85–0.89 and 0.75–0.82, respectively).