A new system has been overtaking the microscope as a tool for diagnosing pathogens. Whole-slide digital imaging may soon be adopted as the primary method for diagnosic surgical pathology, possibly replacing conventional light microscopy as the standard of care. But questions remain as to how it should pass through the regulatory process.

The FDA Hematology and Pathology Devices Panel of the Medical Devices Advisory Committee met in October 2009 with experts in the field to discuss the technology and whether to require a premarket approval (PMA) process or a 510(k) clearance, and the debate is ongoing. At issue, according to transcripts of the hearing, was whether “digital whole-slide imaging [WSI] can be used safely to capture histomorphologic and cytologic features of hematoxylin and eosin (H&E) glass slides for subsequent digital review by pathologists to render pathologic diagnoses of routine surgical specimens.”

During the presentation, Tremel Faison, a scientific reviewer for FDA, argued that microscopes are Class I and exempt from premarket notification, with the exception of using the them in combination with a different technology, such as an IVD for use in diagnosis, monitoring, or screening on neoplastic disease. If WSI is used for primary diagnosis of surgical pathology specimens, it “carries the risk of serious public health consequences if erroneous results are rendered using these systems.” Faison concluded that digital whole-slide pathology must be subject to premarket submission requirements.

According to Faison, FDA’s concerns are that WSI could be used in place of light microscopy for all surgical pathology specimens, and if it is, FDA wants to know whether the quality of WSI is such that it could replace the traditional method without compromising diagnoses. She says FDA plans to ensure safety and effectiveness by requiring standardization and by requesting postmarket studies, if deemed necessary.

In regards to how FDA should assess WSI, the College of American Pathologists released a statement for the meeting. It recommended that the agency use intrapathologist variability to validate the safety and efficacy of WSI. That is, FDA should “focus on measuring whether the diagnosis arrived at using whole-slide digital imaging systems is the same as the diagnosis arrived at by the same pathologist using conventional microscopy.”

Other speakers at the conference focused on the enormous benefit the technology could have on pathology, and said that FDA should not make the matter a cut-and-dried situation. “It enables glass slides to be dealt with like digital files,” said Michael Becich, chair and professor of biomedical informatics and pathology at the University of Pittsburgh School of Medicine, during the presentation. Becich related the switch to what happened in radiology with the adoption of picture archiving and communications systems. “For a number of years, there was teleradiology. It was off to the side and in a little corner on separate machinery, and then what happened in radiology practices, teleradiology disappeared because it all became digital.”

Becich also refuted the notion that WSI would replace glass slides. “The glass slide is still there,” he said. “In a whole-slide imaging environment, I think we should promote the concept that the pathologist remains in control and can go back to the glass slide and can do all the things they do today.”

According to Becich, both methods use objective tools. “We’re not really talking about changing the way that we acquire images from glass. We’re just changing the way we distribute them.”