Renal biopsy findings in chronic phosphate nephropathy. (a) Case of chronic phosphate nephropathy with abundant intraluminal and intracellular calcifications in distal tubules accompanied by tubular atrophy and fibrosis (hematoxylin and eosin) and (b) a positive histochemical reaction with the von Kossa stain confirms that the tubular concretions are composed of calcium phosphate.