The Papanikolaou (Pap) smear or cytology screening has long been used for cervical screening with reliable results. This can be used for screening of patients with or at risk of AIN.
However, its reliability in the use in AIN is controversial. Many papers report that cytological testing often under-reports AIN grade. Unlike the cervix, which is a fixed structure, taking a cytological sample of the anus can be technically difficult.
In fact the American Guidelines (ASCRS) for the treatment of Anal SCC do not recommend its use.
In European countries, the use of anal cytology is more widespread and although its limitations are accepted it is often used with High Resolution Anoscopy and Histology of concerning lesions to form a complete clinical picture.
In Anal SCC there is not sufficient evidence that cytology alone could be a suitable screening technique.
It is accepted practice that before considering the treatment of an area diagnosed with AIN that a biopsy should be taken for formal histopathology.