Anal cytology screening – sampling anal tissue in order to detect cells that may exhibit pre-cancerous changes (dysplasia) – is practical, easily taught and when compared with biopsy is able to predict anal dysplasia in 97% of cases, a study by University of California Los Angeles has found.
The study, published in the International Journal of STD and AIDS, also showed that screening for anal dysplasia – changes in anal tissue that may predict cancer – revealed very high rates of anal dysplasia in HIV-positive men who have sex with men. Two-thirds of the men referred for screening (n=244) had abnormal anal cytology.
However, anal cytology is less able to predict accurately the degree of anal dysplasia. In 93 patients subsequently referred for high resolution anoscopy and biopsy, the extent of agreement between grading of anal dysplasia by cytology and biopsy was only 55%, suggesting that in cases where cytology results in a positive indication of dysplasia, further investigation will be necessary in order to determine the clinical stage of any changes. Anal cytology underestimated the degree of dysplasia.
Anal cytology was carried out by primary care physicians who received one training session in taking a swab from the anus, and cell samples were graded using the same terminology as for cervical cancer: atypical (ASC-US); atypical, cannot rule out high grade lesion (ASC-H), low grade intraepithelial lesions (LSIL) or high-grade squamous intraepithelial lesions (HSIL).
Cranston RD et al. The prevalence of abnormal anal cytology and the predictive value of abnormal anal cytology to diagnose anal dysplasia in a population of HIV-positive men who have sex with men. Int J STD & AIDS 18: 2007.