In this study the diagnostic reliability of a fully digital slide based system, comparing it with the routine conventional optical microscope procedure was evaluated. Our results are in line with previously published studies in the field, where authors reported 94-98% accuracy of digital diagnoses [15–18]. Besides analyzing the results according to the origin of the samples and the types of errors we measured the effects of the pathologists' interpretative skills and experience on the diagnostic results.
In 27/306 - 8.82% - the consensus diagnoses were coherent with the digital diagnoses and overwrote the original OM-based diagnoses (reassessed case). We defined a list of samples according to their origin where DM could be used securely, based on comparing the incoherency-ratio of the specific samples to the overall ratio of the reassessed cases. The incoherency-ratio was below 8.82% - therefore we state that DM could be used equivalently to OM in our Institute in this set of circumstance - in cases with samples from liver, lymph node, kidney, colon, and breast. In this series the results nicely correlate with the incidence of the type-IV errors and confirm our statement. Interestingly hematology cases of lymph nodes fell into this category. As the quality of IHC digital slides were evaluated very good, the explanation of this observation could be the explicit importance of the IHC-profiles in haematopathology. This series of samples are specific for our institute in this set of circumstances. A similar method could be useful for pathology departments in the future when introducing DM in the routine practice in order to maintain patient safety.
Our further investigations estimated the type of errors resulting misinterpretation. Despite the evolution of the scanner systems that resulted in significant acceleration in scanning speed and better digital image quality the DS itself plays an important role in the success of the diagnostic process . The mean quality of DS was 4.43/5. Excluding the slides from the misdiagnosed cases this rate is higher, 4.48/5, taking into account only the slides of the incoherent cases the result is 4.04/5, for the Giemsa stained slides in misdiagnosed cases it is 3.86/5 which is the worst result in any of the measured slide set along with the 3.70/5 result of the special stains. (Figure 1) However we have not recorded any complaints because of missing the 3rd dimension z-coordinate, solutions to provide the pathologist with fine focusing ability on the DS are on the way and may enhance the acceptance of DS .
As no errors was recorded due to misinterpretation of an IHC-DS, our results suggests that the scanner systems in our constellation are sufficient to produce suitable DS from IHC-samples, as others reported similar results and explain the success and spreading of DS-based automated IHC evaluation techniques [21–23]. The most common reason for rating slide quality poor, was that large areas of the slides are out of focus. As this default is detectable by the examiner it never resulted in type II or type IV error. Interestingly the special stains (such as the PAS, Grocott, Prussian-blue, orcein etc.) showed bad result and the reason for this was poor color fidelity in the majority of the cases.
According to our results one of the most important factor of the diagnostic accuracy using DS, is the pathologist's experience in a specific field. There is an increase of diagnostic accuracy signing out only field-specific cases by the pathologists. There was significant negative correlation between diagnostic confidence and individual pathologist's experience. These results indirectly suggests that the impact of the pathologist's age is a major factor for dislike and mistrust DS, as usually more experienced the pathologists the older they are.