The Bethesda System. A proposal for reporting abnormal cervical smears based on the reproducibility of cytopathologic diagnoses.

In the Bethesda System, noninvasive squamous abnormalities are classified as atypical squamous cells of undetermined significance (ASQUS), low-grade squamous intraepithelial lesions, and high-grade squamous intraepithelial lesions. The Bethesda System eliminates two diagnostic distinctions that are made in the dysplasia/carcinoma in situ and cervical intraepithelial neoplasia (CIN) classifications, CIN1 vs koilocytotic atypia and CIN2 vs CIN3, and maintains three others, negative vs ASQUS, ASQUS vs koilocytotic atypia, and CIN1 vs CIN2. To determine whether the diagnostic distinctions preserved in the Bethesda System are made more consistently than those eliminated, we analyzed the interobserver reproducibility of two cytopathologists in classifying 257 smears. The findings indicate that the distinctions retained in the Bethesda System are more reproducible than those eliminated. Specifically, cases classified as koilocytotic atypia were distinguished from CIN1 no more reproducibly than predicted by chance, whereas CIN2 and CIN3 were distinguished as consistently as any other pair of diagnoses examined. In 13 cases in which there was interobserver discordance, one reviewer classified the smear as ASQUS and the other reviewer diagnosed CIN2 or CIN3. The findings in this study suggest that smears showing koilocytotic atypia and/or CIN1 may be reported as low-grade squamous intraepithelial lesions without further specification. In contrast, smears showing high-grade squamous intraepithelial lesions may be further classified as CIN2 or CIN3 in accordance with the Bethesda guidelines. Since the diagnosis of ASQUS is applied to smears showing a wide spectrum of changes, management of patients with the diagnosis of ASQUS will be facilitated by providing an explanatory note and/or recommendations when appropriate.