High-grade cervical abnormalities and screening intervals in New South Wales, Australia

Objectives This study aims to determine the association of two versus three year screening intervals with the likelihood of defection of a high-grade cervical abnormality and cervical cancer. Methods Data were obtained from the New South Wales (NSW) Papanicolaou (Pap) Test Register (PTR) and NSW Central Cancer Registry (CCR). Subjects were human papillomavirus (HPV) unvaccinated women aged 20-69 years who had a minimum of two Pap tests with a negative result at their first recorded Pap test (n = 1,213,295). Logistic regression was used to determine the association between screening interval and the likelihood of: (1) a cytological prediction of high-grade abnormality, defined as cervical intraepithelial neoplasia (CIN) 2 or greater; (2) a histologically confirmed high-grade abnormality; (3) a cytological prediction of cervical cancer and (4) a confirmed diagnosis of cervical cancer, controlling for potential confounders of age and socioeconomic status (SES) of area of residence. Results For each year increase in the screening interval, the odds of a histologically confirmed high-grade abnormality increased significantly in women aged 20-29 years (odds ratio [OR] 1.24, 95% confidence interval [Cl] 1.20-1.28) and in women aged 30-49 years (OR 1.11, 95% Cl 1.06-1.16), but not in women aged 50-69 years (OR 1.08, 95% Cl 0.89-1.32). Similar results were observed for cytologically detected high-grade abnormalities. The screening interval was significantly and positively associated with a cytological prediction of cervical cancer (OR 1.40, 95% Cl 1.28-1.54) and a confirmed cervical cancer diagnosis (OR 1.66, 95% Cl 1.33-2.07) in women aged 20-69 years. We estimate that if the screening interval were increased from two to three years, and the number of women participating in triennial screening participation was the same as for biennial participation in NSW, then 267 (95% Cl 186-347) extra cases of high-grade abnormalities would be detected annually by cytology and 225 extra cases (95% Cl 160291) confirmed by histology, mostly confined to women aged 20-49 years. Equivalently, 2.3 (95% Cl 1.8-2.8) and 1.9 (95% Cl 1.5-2.4) extra cases of high-grade cytology and histology, respectively, would be expected per 1000 women with initially negative cytology if the screening interval were extended from two to three years. Conclusion Increasing the cervical screening interval from two to three years would be expected to significantly increase the odds of detection of a high-grade abnormality for NSW women aged 2049 years and cervical cancer for NSW women aged 20-69 years. Accordingly, our study provides evidence in support of retaining the recommended cervical screening interval at two years for HPV unvaccinated, well women.