Validity of the Vaginal Gram Stain for the Diagnosis of Bacterial Vaginosis

OBJECTIVE: To determine the sensitivity and specificity of vaginal Gram stain as interpreted by the Nugent criteria for the diagnosis of bacterial vaginosis, and to consider the use of Gram stain as the criterion standard for the diagnosis of bacterial vaginosis. METHODS: A multicenter study was conducted of women attending gynecology or sexually transmitted disease clinics. Clinical data consisting of vaginal pH, "whiff test," clue cells, and appearance of the vaginal discharge (Amsel criteria) were compared with the vaginal fluid Gram stain (Nugent criteria) for the diagnosis of bacterial vaginosis. RESULTS: The sensitivity and specificity of the Gram stain compared with the Amsel criteria were 89 and 83%, respectively. There was significant variation in the specificity values by geographic site. If the Gram stain was considered the criterion standard for the diagnosis of bacterial vaginosis, the sensitivity and specificity of the Amsel criteria were 70 and 94%, respectively. CONCLUSION: The vaginal Gram stain (Nugent criteria) is a sensitive method for the diagnosis of bacterial vaginosis. The 83% specificity suggests that the currently used Amsel criteria may lead to the underdiagnosis of bacterial vaginosis.