Incidence of atypical glandular cells of uncertain significance in cervical cytology following introduction of the Bethesda System

Objective. To establish the frequency of the atypical glandular cells of uncertain significance (AGCUS) category, and its subcategories, as defined by the Bethesda System (TBS). Methods. Our computerized records of cervical/vaginal cytology specimens submitted from January 1, 1993, through December 31, 1995, were retrospectively reviewed for specimens diagnosed as AGCUS. When appropriate, our subcategory of 'AGCUS favor premalignant/malignant lesion' was further qualified as 'favor endocervical adenocarcinoma in situ' or 'suspicious for endometrial carcinoma.' The number of specimens and patients diagnosed for each subcategory were grouped by calendar year. Differences in frequency between time periods were tested for statistical significance using χ2 analysis. Results. AGCUS was diagnosed in 1181 of 177,715 submitted specimens (0.66%). The frequency of subcategories was as follows: 'favor reactive' (65%), 'unable to further classify' (30%), 'favor premalignant/malignant' (2.9%), 'suspicious for endometrial carcinoma' (1.9%), and 'favor endocervical adenocarcinoma in situ' (0.4%). From 1993 to 1995 there was an increase in the rate of diagnosis of AGCUS (0.55 to 0.73%; P < 0.001) and a decrease in the percentage of specimens with AGCUS subclassified as 'favor premalignant/malignant' (6.2 to 0.5%; P < 0.001). Other subcategories showed no significant change in frequency over this time period. The rate of biopsy-proven preinvasive or invasive lesions in AGCUS patients also showed no significant change from year to year over this time period. Conclusion. The AGCUS diagnosis can be anticipated at a low but consistent rate from a cytology laboratory using TBS. Any comparison of laboratories should take into consideration the change in reporting frequencies that occurs as part of the 'learning curve' following introduction of TBS reporting. Uniform diagnostic criteria and additional reports with large numbers of cytologic specimens will be needed to establish the expected frequency of AGCUS and its subcategories.