Nasr SH et al. (2007) Thin basement membrane nephropathy cannot be diagnosed reliably in deparaffinized, formalin-fixed tissue. Nephrol Dial Transplant 22: 1228–1232

Glutaraldehyde-fixed, plastic-embedded tissue is preferred for electron microscopy (EM)-based diagnostic renal pathology. If no glomeruli are present on glutaraldehyde-fixed sections, tissue originally fixed in formalin and embedded in paraffin for light microscopy can be deparaffinized and embedded in plastic resin for EM. A recent report shows, however, that reprocessing tissue in this way can cause artifactual thinning of the glomerular basement membrane (GBM) that prevents accurate diagnosis of thin basement membrane nephropathy (TBMN).

Formalin-fixed, paraffin-embedded tissue blocks from 21 renal biopsies (8 TBMN, 6 minimal-change disease, 2 histologically normal, and 5 diabetic nephropathy) were reprocessed, and examined using EM. Glutaraldehyde-fixed, plastic-embedded tissue from all 21 biopsies had previously been examined by EM. For each biopsy, 80 measurements of the GBM were made on glutaraldehyde-fixed tissue, and 80 on deparaffinized formalin-fixed tissue.

Reprocessing of formalin-fixed tissue resulted in considerable GBM thinning in all 21 cases. The mean decreases in GBM thickness with formalin-fixed tissue compared with glutaraldehyde-fixed tissue were 23% (P = 0.004) for TBMN biopsies, 40% (P = 0.004) for normal and minimal-change disease biopsies, and 34% (P = 0.031) for diabetic nephropathy biopsies. On deparaffinized formalin-fixed tissue, four of the six minimal-change disease cases had a mean GBM thickness below the laboratory's threshold for TBMN diagnosis (<250 nm for males and <220 nm for females), and would have been incorrectly diagnosed as TBMN. No clear criteria could be identified for accurate TBMN diagnosis in formalin-fixed tissue.