Objective: To compare anal cytology prepared via conventional methods and the ThinPrep processor.
Study design: Cells from the anal canal were collected using a moistened swab. One hundred thirty-six samples were collected from 133 gay or bisexual men; 102 were human immunodeficiency virus seropositive. A conventional smear was prepared and fixed in 95% ethanol. The residual cells on the swab were collected for thin-layer preparation using the Cytyc processor.
Results: The diagnoses made from the conventional smears and thin layers agreed in 113 of 136 cases. An additional 19 cases were classified within one diagnostic category of each other. Two cases of low grade squamous epithelial lesion (SIL) diagnosed on the ThinPrep were judged negative on the conventional smear. Similarly, two cases of low grade SIL diagnosed on the conventional smear were judged negative on the thin-layer preparations. Rectal columnar cells were present on 127 of the ThinPrep samples but on only 113 of the conventional smears.
Conclusion: ThinPrep and conventional smears of the anal canal yielded similar diagnoses. Rectal columnar cells were more frequently encountered on the thin layers; their presence is an indication that the rectal transformation zone may have been adequately sampled. In addition, the ThinPrep technique reduces fecal and bacterial contamination and air-drying artifact, which frequently hinder cytologic evaluation of the anal canal.