ThinPrep® whole-slide digital images vs conventional microscopy in NILM, ASC-US and LSIL cervical lesions: European Federation of Cytological Societies (EFCS) study

Introduction: High inter- and intraobserver variability is acknowledged in Negative for Intraepithelial Lesion or Malignancy (NILM), Atypical Squamous Cells of Undetermined Significance (ASC-US) and low-grade squamous intraepithelial lesion (LSIL) diagnostic categories in cervical cytology. As digital cytology (DC) has emerged, whole-slide images (WSI) have been compared to conventional light microscopy (LM) to evaluate its feasibility in routine practice. Methods: Six cytopathologists evaluated 20 liquid-based cervical samples diagnosed as ASC-US, LSIL or NILM with known hrHPV status, both by conventional LM and WSI, equalling 240 evaluations. Interobserver agreement was measured using Fleiss’s Kappa, Kendall´s coefficient and interclass correlation (ICC). Results: Most of the samples (93.75%) were assigned to the same original range of categories: NILM 5 (25%), ASC-US 10 (50%) and LSIL 5 (25%). WSI versus LM interobserver agreement varied with Fleiss’s Kappa (0.324 versus 0.319), Kendall’s W (0.670 versus 0.572) and ICC (0.585 versus 0.414). Interobserver agreement for the ASC-US category was higher in Kendall’s W (0.435 for WSI versus 0.329 for LM) and in ICC (0.394 versus 0.118). Fleiss’s kappa showed lower interobserver agreement for ASC-US in WSI than LM (0.000 versus 0.039). Conclusion: This study illustrated that despite overall better agreement in WSI, ASC-US results were less favourable in WSI than LM, according to Fleiss’s kappa test, but not other tests.