ASCUS stands for “atypical squamous cells of undetermined significance”. It is a designation given to pap smears when the cells are not frankly abnormal but they are not perfectly normal either. It is a borderline designation. ASCUS pap smears are usually normal but there is a small chance of an abnormality in the cervix. When pap smear comes back ASCUS a secondary test is done to look for high risk forms of HPV. An ASCUS pap smear with a negative high risk HPV screen is treated like a normal pap smear, it is just as likely to represent an abnormal cervix as a normal pap. If the HPV is positive with an ASCUS pap, a colposcopy is usually done.
When a pathologist reads a pap smear they are presented with a bunch of random cells on a slide. Their job is to decide if these cells come from a normal cervix or if they come from an abnormal cervix. They also try to give some idea how abnormal things appear. In some cases, it is not completely clear whether the cells are more consistent with an abnormality or not. In these cases the ASCUS designation is given. Because certain high risk strains of HPV are associated with cervical dysplasia, the presence of high risk HPV is used to further look into an ASCUS pap smear. If those strains are present along with an ASCUS pap, that is enough reason to look further and do a colposcopy.
The ASCUS designation of pap smear is the least abnormal of any pap apart from a pap smear read as normal. Women with ASCUS pap smears usually do not have any problem with the cervix. In the case where there is a cervical abnormality, it is usually very early and often does not need treatment.