Interobserver variability in subclassification of squamous intraepithelial lesions: Results of the College of American Pathologists Interlaboratory Comparison Program in Cervicovaginal Cytology

To determine whether, on a national cytology proficiency test, a competent cytologist can consistently distinguish grades of squamous intraepithelial lesions. Results for low- and high-grade squamous intraepithelial lesion referenced slides from the College of American Pathologists Interlaboratory Comparison Program in Cervicovaginal Cytology for 1996 and 1997 were analyzed including educational, nongraded vs graded validated slides. The discrepant rate between low- and high- grade lesions ranged from 9.8% to 15% for cytotechnologist, pathologist, laboratory, and all responses. There was a statistically significant difference in performance on graded, validated slides vs educational slides with better performance on validated slides. This significant interobserver variability in subclassification of squamous lesions should be considered in management guidelines for abnormal Papanicolaou test results and implementation of national cytology proficiency testing.