Papanicolaou tests with mixed high-grade and low-grade squamous intraepithelial lesion features: Distinct performance in the College of American Pathologists Interlaboratory Comparison Program in Cervicovaginal Cytopathology

Context. - Previous studies have shown that in gynecologic cytology, cases of low-grade squamous intraepithelial lesion (LSIL) and high-grade squamous intraepithelial lesion (HSIL) perform differently on interpretive review. The performance of cases with mixed LSIL and HSIL features is unknown. Objective. - To compare the performance of gynecologic cytology cases of "pure" LSIL and HSIL with cases showing mixed LSIL and HSIL features. Design. - We compiled performance data from the College of American Pathologists Interlaboratory Comparison Program in Cervicovaginal Cytopathology from the years 2003 and 2004, and compared the performance of slides showing relatively pure LSIL and HSIL (≤10% misclassification as HSIL and LSIL, respectively) with slides showing mixed LSIL or HSIL features (cases misclassified as LSIL or HSIL >10% of the time). Results. - Interpretations from a total of 4508 cases (2452 HSIL and 2056 LSIL) were analyzed. Overall, the sensitivity of participants on slides with a reference diagnosis of HSIL was 97.3%, and of LSIL was 95.9%. Performance trends for pure versus mixed cases varied by slide type and reference diagnosis. For conventional slides, participant sensitivity on pure HSIL cases was greatest (98.0%) and on pure LSIL cases was least (95.2%), while participant performance on cases with mixed features was intermediate (97.0% for mixed HSIL and 96.7% for mined LSIL). In contrast, participant performance on ThinPrep slides showed the greatest sensitivity for mixed LSIL slides (97.9%), while performance on mixed HSIL slides showed the lowest sensitivity (95.7%); slides with pure features had intermediate sensitivity levels (96.3% for both HSIL and LSIL). Further evaluation demonstrated that conventional pure HSIL slides performed significantly better than mixed HSIL slides (P = .006), whereas mixed LSIL slides performed better than pure LSIL slides (P = .01). For ThinPrep slides, pure HSIL cases performed similarly to mixed HSIL cases (P = .43), while mixed LSIL cases performed better than pure LSIL cases (P = .04). Conclusion. - Slides with mixed LSIL and HSIL features have measurably distinct performance characteristics in comparison to slides with pure LSIL or HSIL features. Participant performance on conventional mixed cases is distinctly different from performance on ThinPrep mixed cases.