Digital vs traditional: Are diagnostic accuracy rates similar for glass slides vs whole slide images in a non-gynaecological external quality assurance setting?

Introduction: The Royal College of Pathologists of Australasia Quality Assurance Programs introduced virtual microscopy cases into its cytopathology non-gynaecological programme after a short pilot phase, to address the challenges of providing a purely glass slide-based external quality assurance programme to multiple participants both locally and internationally. The use of whole slide image (WSI) cases has facilitated a more robust programme in relation to standardised material and statistical analysis, with access to a wider variety of specimen types and diagnostic entities.

Method: Diagnostic accuracy rates on 56 WSI were assessed against the reference diagnosis. A portion (12) of these WSI slides had been used in glass slide format in previous external quality assurance surveys, and the results of these were compared to the responses received as glass slide cases.

Results: Overall diagnostic accuracy for the 56 WSI cases was acceptable in comparison to the reference diagnosis. When these 12 cases were analysed individually, for seven of the 12 cases, virtual format was found to be not inferior to glass slides for diagnostic accuracy. For one case, accuracy using WSI for diagnosis was superior to glass format.

Conclusion: Diagnostic accuracy, using WSI for cases in our external quality assurance programme is acceptable. As the use of digital microscopy in a large scale external quality assurance programme offers extensive advantages over a glass slide-based format, our results encourage future comparison of diagnostic accuracy for virtual compared to glass slide format at a point in time where pathologists are becoming increasingly familiar with virtual microscopy in everyday practice.