However, a Pap smear cannot be relied upon to detect all HPV infections because it is not designed specifically to detect HPV DNA . Despite its contribution to the decreased incidence of cervical cancer, cytology has shortcomings that cause both false negative and false positive results, leading to missed disease or to unnecessary patient anxiety and over-treatment. Cytology is complex, requiring intense visual review of cells. The technique is subjective and plagued by inter- and intraobserver variability. Incorrect or poor sampling can lead to false negative or inconclusive results.
Aggressive cancers can occur between screening intervals.
The Pap smear is only a snapshot of the present condition of the cervix. Two-thirds of preventable cervical cancers occur in women who have not had a Pap test in at least five years. The symptoms of HPV infection can appear weeks, months, or even years after initial infection, so it is possible to become infected without being aware of it. Women infected during their teenage years may show no signs of infection until their thirties or forties, or may not develop any symptoms at all. The risk of HPV infection is also thought to be influenced by other variables such as age, oral contraceptive use, and smoking.