Even though your sister and your daughter had the exact same pap smear showing atypical squamous cells of undetermined significance with a positive HPV, the implications and the management are very different based on their ages. We do not routinely test for the HPV virus under the age of 30 because it is a common and transient viral infection. It most often goes away with time, and if not associated with a significant abnormality on pap smear, is of little significance.
Under the age of 30 we do “reflex” testing for HPV, which means that if the pap smear comes back showing any abnormality (in this case atypical cells of undetermined significance), the laboratory will then do a reflex test to detect the presence or absence of the high risk types of the HPV virus.
There is a special subgroup of women between the ages of 21 and 24, where less aggressive measures are taken for minor abnormalities in pap smears (either atypical cells or even a pap that is consistent with low grade dysplasia). In this age group, because of the often transient nature of HPV and because of the low risk of cervical cancer in this age group, along with the risks associated with over treating young women of childbearing age, close follow up with a pap smear in a year is all that is recommended.
If the changes on next years' pap smear are still consistent with only atypical cells or low grade changes, continued close follow up with pap smears alone under the age of 24 is still preferred and recommended. Over the age of 24, colposcopy would be warranted with atypical cells on pap with a positive HPV.