Differential diagnosis in nephropathology: an immunofluorescence-driven approach

Evaluation of a renal biopsy can be intimidating, because observational data from histologic stains, direct immunofluorescence (IF), and electron microscopy must be integrated with clinical and laboratory data to arrive at the correct diagnosis. Numerous diagnostic categories usually merit consideration. The typical strategy to diagnose renal disease is heavily weighted toward analysis of the histologic pattern of glomerular injury. This focus on histology is understandable; histologic evaluation was the first analytic probe available and has driven the formulation of classification schemes. Evaluation of IF before review of the light microscopy facilitates diagnostic evaluation, because the possibilities are immediately reduced. This simplifies the crucial final step-clinical and histologic correlation. In this review, I discuss the information content of IF and provide an algorithmic approach to the major renal diseases based on an IF-driven dissection of the differential diagnosis.