Beyond diagnosis: stage and grade in inflammatory renal disease

The renal biopsy can provide valuable prognostic information in addition to a diagnosis. Most important are markers of histological activity (grade) and chronicity (stage). There are many systems for assessing and classifying grade and stage in inflammatory renal disease; many suffer from difficulties in application and reproducibility and none has achieved universal acceptance. In this article, we discuss various methods for classifying three common renal diseases: lupus nephritis, microscopic (ANCA-associated) vasculitis and IgA nephropathy. Even if a formal system of classification is not used, some basic information relating to ‘grade and stage’ should be included in all renal biopsy reports, and these form the basis of our recommendations. Newer morphometric and molecular techniques offer a different, potentially more objective, approach to grading and staging, but their application to routine clinical practice is not without difficulties and, for the most part, these remain research tools.