PLT07 Decreased HPV Detection in Unsatisfactory Cervicovaginal Cytology: Quality and Safety Implications for Primary HPV Screening?

ASCCP guidelines state that unsatisfactory cytology with negative or not available HPV testing should undergo repeat screening in 2-4 months as a negative HPV result could reflect an inadequate sample. We examined the rate of HPV detection in unsatisfactory cytology in the setting of frequent co-testing to explore the theoretical impact of inadequate collections in an HPV primary screening program.

Pap smear cytology that underwent glacial acetic acid reprocessing (GAA) for initial blood-related inadequacy was analyzed over a one-year period. HPV testing was performed using the Roche cobas® assay. 

We observed a significantly lower HPV positivity rate in truly unsatisfactory paps (meaning those that were not adequate after GAA). We hypothesize that this is due to pre-analytic factors (low epithelial cell cellularity). Interestingly, given that some HPV assays such as cobas® use a ß-globin internal control, it is possible that bloody inadequate paps return an HPV negative result rather than a more appropriate inconclusive/invalid result due to RNA present in blood elements (while anucleate, red blood cells are know to contain abundant mRNA transcripts). An epithelial cell specific internal control could potentially overcome these putative false negatives, a feature that would be particularly beneficial for maximizing the safety and reliability of an HPV primary screening program. Finally, our results suggest that a laboratories ability to use unsatisfactory rates as a pre-analytic quality indicator may be compromised when cytology is performed only on HPV positive samples. 

709 of 781 initially unsatisfactory paps treated with GAA converted to adequate (91%, Figure 1). 479 of these (68%) had an accompanying HPV testing, with an HPV positivity rate of 16.1% (77/479) (Figure 2). This was not significantly different than the lab-wide positivity rate (15.7%). However, for the 56 of the 72 paps that remained unsatisfactory and had an accompanying HPV testing (77%), there was a significantly lower HPV positivity rate of 1.8% (1/56) (p = 0.004). 

Quality Assurance + Patient Safety