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Pathology Organizations Update Guideline on Validating Whole-Slide Imaging Digital Pathology Systems

NEW YORK ─ The College of American Pathologists, American Society for Clinical Pathology, and Association for Pathology Informatics this week released an updated guideline on validating whole-slide imaging systems for diagnostic use.

The guideline, published in the Archives of Pathology & Laboratory Medicine, updates previous guidance released in 2013 and provides three "strong recommendations" and nine "good practice statements" to assist laboratories with validating whole-slide imaging, or WSI, digital pathology systems.

The group's first strong recommendation calls for whole-slide imaging validation to include a sample set of at least 60 cases for one application or use case. Examples of use cases include hematoxylin-eosin-stained sections of fixed tissue, frozen sections, and hematology, and they should "reflect the spectrum and complexity of specimen types and diagnoses likely to be encountered during routine practice," the authors wrote.

A second recommendation stated that a validation study should demonstrate that a user can reach the same diagnostic conclusion using digital and glass slides. If diagnostic concordance is less than 95 percent "laboratories should investigate and attempt to remedy the cause." In the third strong recommendation, the group said that "a washout period of at least two weeks should occur between viewing digital and glass slides."

The authors also provided nine good practice statements that they defined as having a ‘"high level of certainty that the recommendation will do more good than harm (or the reverse), but where there is little direct evidence."

Among the good practice statements, the authors said that all pathology laboratories implementing whole-slide imaging technology for clinical diagnostic purposes should conduct their own validation studies. Further, "validation should be appropriate for and applicable to the intended clinical use and clinical setting of the application in which WSI will be used," and "validation of WSI systems should involve specimen preparation types relevant to the intended use," the authors said.

To create the guidelines, the College of American Pathologists convened an expert panel that assessed evidence published since the release of the 2013 guideline. The multidisciplinary expert panel included pathologists with experience in WSI, two histotechnologists, and a research methodologist.

The panel performed a systematic review of the literature that included frozen sections, anatomic pathology specimens, and hematopathology cases, but excluded cytology cases. The experts selected studies for the systematic review of evidence if they referred to whole-slide imaging, reflected clinical use or investigative research, and was a peer-reviewed, full-text article.

The specific aim of the updated guideline is "to ensure pathologists make accurate diagnoses to at least the same level as light microscopy, and to identify and control interfering artifacts or technological risks that WSI could introduce to patient safety," the authors said.