A Comparative Evaluation of the Papanicolaou Test for the Diagnosis of Trichomoniasis

BACKGROUND: Trichomoniasis is the most prevalent nonviral sexually transmitted disease in humans worldwide. In addition to its pathologic implications, trichomoniasis is a risk factor for the transmission of the HIV and is associated with reproductive complications in females. Diagnosis of the disease is problematic due to inadequate accuracy of current diagnostic methods. Recently developed DNA-based techniques for detection of Trichomonas vaginalis seem to be promising alternatives. GOAL: The goal of this study was to evaluate the accuracy of the Papanicolaou test for the diagnosis of trichomoniasis by comparing polymerase chain reaction (PCR) with other current diagnostic methods. STUDY DESIGN: A total of 1008 cervicovaginal swab specimens from a randomized population attending a gynecological service were analyzed in this study. In addition to current diagnostic methods, two sets of specific primers were used for PCR detection of T vaginalis in the cervicovaginal DNA samples, with a PCR quality control. Different examiners conducted PCR and Papanicolaou analyses in a double-blind trial. RESULTS: The prevalence of trichomoniasis in this population was 6%. A considerable number of diagnostic results of the Papanicolaou test were false negative or false positive. Compared with PCR, specificity of the Papanicolaou test was 97.6%, whereas sensitivity was only 60.7%. The positive predictive value of the Papanicolaou smear was 61.7%. These results suggest that irregularly shaped parasites without clearly defined nuclei and flagella and bacteria-induced focal cytolysis limit the ability of the Papanicolaou test to detect T vaginalis. CONCLUSION: The Papanicolaou test, the most readily available cytologic method for screening sexually transmitted pathogens and cellular abnormalities in most developing countries, is inadequate for the diagnosis of trichomoniasis due to its inherent limitations. However, PCR is a highly sensitive and specific test for the diagnosis of trichomoniasis.