Researchers have proposed that an anal cancer screening program similar to cervical cancer screening, using anal cytology followed by referral of patients with abnormal results to high-resolution anoscopy and subsequent treatment of biopsy-proved AIN, may prevent the development of anal cancer. The reported sensitivity and specificity of anal cytology relative to findings at biopsy (sensitivity, 69%-93%; specificity, 32%-59%, respectively) are similar to findings in studies comparing cervical cytology and cervical biopsy for the prevention of cervical cancer.
Although the Centers for Disease Control and Prevention does not recommend anal cytology screening, other organizations such as the New York State Department of Health do recommend annual anal cytology for MSM and any HIV-positive patients with a history of anogenital condylomas. Among patients with HIV- or HPV-related lesions, histologic signs of dysplasia are apparent in more than one-fifth of those who undergo testing. Among HIV-positive MSM, the positive predictive value of abnormal anal cytology to predict anal dysplasia is approximately 95%.15
The goal of anal cytology is to identify patients with cellular changes in the epithelial cells that line the anal canal; any patients with atypia are then referred to undergo high-resolution anoscopy. No specific preparation is necessary before anal cytology, though patients should be instructed to refrain from receptive anal sex and enemas for 24 hours before testing. If a digital rectal examination is performed in conjunction with anal cytology, the cytologic sample must be obtained before lubrication is introduced into the anal canal. The standard technique used in obtaining anal cytologic specimens involves inserting a water-moistened Dacron swab into the anal canal to above the squamocolumnar transition zone, approximately 2 cm (1 inch) from the anal verge. While mild external pressure is applied to the anal wall, the swab is gently manipulated in a craniocaudal and circular motion within the canal. After several rotations, the swab should be withdrawn and immediately immersed in methanol-based preservative-transport solution.