Follow-up of Papanicolaou smears diagnosed as atypical squamous cells of undetermined significance.

In the first year since the institution of the Bethesda system at UCDMC, 549/7,388 (7.43%) Papanicolaou (Pap) smears were diagnosed as having an epithelial abnormality. One hundred ninety-three of the 549 (35.1%) of the abnormal smears received an ASCUS diagnosis, representing 2.61% of the total volume. Follow-up was obtained on 124/193 (64.2%) and consisted of colposcopy with biopsy in 38.3%, one repeat Pap smear in 51.2%, and two or more repeat Pap smears in 10.5%. Follow-up revealed a squamous intraepithelial lesion (SIL) in 29.1%, ASCUS in 12.9%, and no evidence of an epithelial lesion in 58.0%. Review of the original ASCUS Pap smear from the group with no epithelial lesion on follow-up showed increased inflammation plus metaplasia and/or reactive changes in 69.5% and ASCUS in 19.5%. This study demonstrates that a significant percentage of ASCUS Pap smears represent SIL. However, many Pap smears with reactive, inflammatory changes are misclassified as ASCUS and would be best diagnosed under "Reactive/Reparative Changes" in the Bethesda system. Careful attention to criteria for ASCUS and inflammatory and reactive atypia is recommended to avoid misclassification and to make this category more meaningful to the clinician.