Projected Impact of HPV and LBC Primary Testing on Rates of Referral for Colposcopy in a Canadian Cervical Cancer Screening Program

Objective: To estimate the impact of implementing primary human papilloma virus liquid-based cytology (LBC) screening on four-year rates of referral for colposcopy in the British Columbia screening program. Methods: We used data on referral for colposcopy from an RCT (HPV FOCAL) comparing HPV testing every four years with LBC testing every two years. We also used data from population screening with conventional cytology among women aged 25 to 69. The predicted effect of adoption of either trial protocol on rates of referral for colposcopy was estimated using trial age specific result and screening result-specific rates weighted by their screening program distribution. The cumulative age-specific rates of referral for colposcopy over four years were calculated. Results: Use of HPV testing initially increased rates of referral for colposcopy in the trial, but over four years the cumulative rates of referral were similar to those for LBC except in women aged 25 to 29, in whom a substantial excess persisted. Four-year rates of referral for colposcopy declined with age in women screened with HPV testing, LBC, and conventional cytology. Extrapolating the trial results to the distribution in the provincial screening program, implementation of either HPV or LBC throughout the provincial population would approximately double the current rates of referral for colposcopy. Conclusion: Compared with LBC screening, primary screening for HPV increased rates of referral for colposcopy only among women aged 25 to 29. In contrast to current practice, referral for colposcopy was largely driven by the trial protocol recommendations for the management of abnormal results and not by which screening test was used.