Is the Papanicolaou smear useful for diagnosing sexually transmitted diseases?

To examine the validity of cervical cytologic diagnosis of sexually transmitted diseases, we reviewed the literature and calculated the efficacy of the Papanicolaou smear as a diagnostic technique. The predictive value of a positive test varied widely, but was generally higher for Trichomonas vaginalis (0.81-1.00) than for other organisms. For Chlamydia trachomatis, the predictive value of a positive test ranged from 0.40-1.00. Cytologic diagnosis of sexually transmitted diseases has not been studied adequately, but the available literature suggests that its sensitivity is low. In general, the Papanicolaou smear should not be used to diagnose sexually transmitted diseases, and treatment should not be based on cytologic findings alone. At best, cytologic indications of sexually transmitted diseases should prompt a definitive laboratory test.