Cast formation in the renal tubules


With renal tubular injury, epithelial cells slough into the lumen of the renal tubules and are caught up within a mucoprotein matrix made from Tamm-Horsfall protein (hyaline cast). This forms a cellular cast. With time, the epithelial cells degenerate and can no longer be recognized as cells within the hyaline matrix, thus forming coarsely granular, then finely granular, casts. Waxy casts are the final step in the formation of casts and usually indicate chronic tubular disease.