Difficult diagnoses in renal pathology: Evidence from EQA schemes

Abstract

The UK National External Quality Assessment Schemes in renal pathology and renal transplant pathology have accumulated evidence on the problems encountered by diagnostic histopathologists in routine practice. These can be subdivided into qualitative (getting the diagnosis right) and quantitative (achieving consistency in assessing the severity of a process). Some cases simply present difficult diagnostic problems. But in the qualitative group, problems often arise because descriptive terms (such as focal segmental glomerulosclerosis (FSGS) or interstitial nephritis) are accepted as a ‘diagnosis’ without further thought to explaining the underlying cause of the pattern. This often demands clinical, biochemical and serological information; the renal pathologist should be capable of discussing such evidence with nephrologists. There is sometimes a tendency to overdiagnose recently described or ‘fashionable’ diseases. In transplant pathology, early (and potentially catastrophic) antibody-mediated rejection is particularly easily missed, as is polyoma virus infection. In transplant pathology, the main quantitative problem is the evaluation of acute rejection and chronic allograft nephropathy, in which, despite the development of the Banff classification, interobserver variation remains high. Quantitation is an obvious problem in native renal biopsies in evaluating lupus nephritis, but an assessment of disease ‘grade and stage’ is likely to be important when reporting most biopsies.