Pathologic Evaluation of Canine Renal Biopsies: Methods for Identifying Features that Differentiate Immune‐Mediated Glomerulonephritides from Other Categories of Glomerular Diseases

<jats:sec><jats:title>Background</jats:title><jats:p>Human renal biopsies are routinely evaluated with light microscopy (<jats:styled-content style="fixed-case">LM</jats:styled-content>) using a panel of histologic stains, transmission electron microscopy (<jats:styled-content style="fixed-case">TEM</jats:styled-content>), and immunofluorescence (<jats:styled-content style="fixed-case">IF</jats:styled-content>) microscopy to obtain a diagnosis. In contrast, the pathologic evaluation of glomerular disease in veterinary medicine has relied mostly on <jats:styled-content style="fixed-case">LM</jats:styled-content> and was of limited utility. To address this problem, recently established veterinary renal diagnostic centers have adopted methods used in human nephropathology for evaluation of renal biopsies. Three broad categories of disease, which have the greatest implications for clinical management of proteinuric dogs, have been established and include amyloidosis, immune complex‐mediated glomerulonephritis (<jats:styled-content style="fixed-case">ICGN</jats:styled-content>), and non‐<jats:styled-content style="fixed-case">ICGN</jats:styled-content>.</jats:p></jats:sec><jats:sec><jats:title>Objective</jats:title><jats:p>To demonstrate histopathologic, ultrastructural, and <jats:styled-content style="fixed-case">IF</jats:styled-content> findings in renal biopsy specimens that experienced veterinary nephropathologists utilize to make accurate and clinically useful diagnoses in dogs with proteinuric glomerular disease and to provide guidelines for the proper evaluation of renal biopsies.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>Renal biopsy specimens were routinely examined by <jats:styled-content style="fixed-case">LM</jats:styled-content>,<jats:styled-content style="fixed-case"> IF</jats:styled-content>, and <jats:styled-content style="fixed-case">TEM</jats:styled-content>. Samples were reviewed by members of the World Small Animal Veterinary Association Renal Standardization Study Group to identify lesions that were diagnostic for, or suggestive of, the presence of immune complexes (<jats:styled-content style="fixed-case">IC</jats:styled-content>) or amyloidosis in all modalities. Ten guidelines for renal biopsy evaluation were formulated.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>Each method of investigation contributed important findings that were integrated to make an accurate final morphological diagnosis. The guidelines were validated by an independent group of veterinary pathologists.</jats:p></jats:sec><jats:sec><jats:title>Conclusions and Clinical Importance</jats:title><jats:p>Routine evaluation of renal biopsies with <jats:styled-content style="fixed-case">LM</jats:styled-content>,<jats:styled-content style="fixed-case"> TEM</jats:styled-content>, and <jats:styled-content style="fixed-case">IF</jats:styled-content> is feasible and necessary for making accurate, morphologic diagnoses that can be used to guide clinical management of dogs with glomerular disease.</jats:p></jats:sec>