Fast Processing of Electron Microscopic Specimen Preserved Ultrastructure of Glomeruli and Electron Dense Deposits in Diagnostic Renal Biopsies: A Prospective and Retrospective Comparative Study.

Optimization of electron microscopy (EM) tissue processing protocols is essential to handle the global increase in the number of renal biopsies requiring EM for accurate diagnosis. The conventional EM processing method (CEM) is the standard method used by >95% of laboratories worldwide and it takes at least 48-52 hours for completion. In contrast, a fast-processing EM method (FEM) using microwave irradiation can be completed in 8 hours, allowing EM findings to be reported within 24 hours for most cases. There is widespread concern about the suboptimal quality of the FEM that may compromise its diagnostic roles; however, qualitative and quantitative data supporting the non-inferiority of FEM compared to CEM has not been reported. We performed both prospective and retrospective studies. The prospective analysis compares FEM and CEM images from the same biopsy samples. For each case, the tissue was divided into two pieces; one piece for FEM processing and the second for CEM processing. The retrospective study compares the EM images of renal cases with electron-dense deposits from our archives that were processed either by FEM or CEM. The prospective analysis included 4 cases: lupus membranous nephropathy, IgA nephropathy, immune-complex mediated glomerulonephritis, and acute tubular injury. Both FEM and CEM methods obtained high-resolution images with comparable quality. A quantitative morphometric analysis of the glomerular basement membrane (GBM) in the IgA nephropathy case showed similar GBM thickness when processed by the FEM and the CEM, suggesting that FEM did not affect GBM thickness. The retrospective study of 42 cases with electron-dense deposits showed that the ultrastructural features of electron-dense deposits were indistinguishable between the FEM and the CEM. This included microtubular substructures in immunotactoid glomerulonephritis, the "fingerprint" deposits in cryoglobulinemic glomerulonephritis, fibril deposits in the light-chain amyloidosis as well as fibrillary glomerulonephritis, with comparable morphometric measurements of the deposits. The FEM is efficient, consistent, reproducible, and delivers comparable high-quality sections and images for diagnostic assessment of renal biopsies, comparable to those attained by the CEM while decreasing turnaround time significantly, making it possible to provide faster and accurate diagnostic results.