HPV positive women need triage. This usually includes an immediate triage test and repeat testing (commonly HPV) after some time in women negative to the first test. Objective was studying how the characteristics of the first test influence the second.
Data from the first survey of routine activity in Italy were used. In Italy HPV positive women have reflex cytology and are referred to colposcopy if it is ASC-US or more severe. If cytology is <ASC-US they repeat HPV after 1 year and are referred to colposcopy if still positive. Aggregated data (by local programme and 5-year age group) were collected on how many women were HPV positive, how many of them had abnormal cytology, were referred to colposcopy immediately or after 1 year and how many had a CIN2 or more severe histology detected during colposcopies performed because of abnormal cytology and because of persistent HPV positivity. The effect of the immediate referral rate to colposcopy (because of abnormal cytology) on the overall referral (either because of abnormal cytology or of persistent infection) was studied by regression. The same was done for the effect of local immediate referral rate and sensitivity of cytology (estimated as proportion of CIN2+ detected as a result of immediate colposcopy) on the overall local detection of CIN2+ .
Ten local programmes with complete data, having screened by HPV over 72,000 women were considered. The proportion of HPV+ women judged to have abnormal cytology varied strongly between local programmes, from 20% to 57%. Nevertheless such changes had very little effect on the overall referral to colposcopy and none on the overall detection of CIN2+. An increase of 10 absolute percent points (e.g. from 10% to 20%) in HPV positive women referred to immediate colposcopy resulted in only a 4.2% (95% CI 3.1 to 5.1) increase of the overall proportion of HPV positive women referred to colposcopy and in a 0.4% (-0.1 to 2.9) increase in the overall detection of CIN2+. An increase of 10 absolute percent points in the sensitivity of cytology resulted in a 1.1% increase (0.1-2.0) in the overall detection of CIN2+.
1-year HPV test repeat limits the effect of subjectivity in cytology interpretation. Most high-grade CIN missed by cytology are detected by HPV after one year. Sensitivity of the first triage test determines only the risk of invasive cancer before re-testing, given the re-testing interval. Increases in sensitivity of the first triage test can be exploited by increasing the interval before repeat HPV. This would allow a greater proportion of HPV infection to clear, thus reducing the overall referral to colposcopy.