Abnormal renal tubule morphology Renal intratubular casts Urinary casts are formed in the distal convoluted tubule or the collecting duct by solidification of protein in the lumen of the kidney tubules. This term refers to casts located within the tubuli of the kidney. More precisely, casts are defined as a material that completely fills and expands the tubular lumen with simplification of surrounding tubular epithelium. Casts are classified as either nuclear debris/granular brown material, red blood cell, white blood cell, myeloma, or myoglobin cast. Tubular casts Casts can be subsequently eliminated via the urine and may be seen by microscopy of the urine sediment, which should be coded separately using an appropriate term from the Cylindruria subhierarchy (HP:0012615). Intratubular casts may have various compositions with different morphologic and staining characteristics. Both hyaline and granular casts may be observed in a number of renal diseases. Commonly observed casts are hyaline (eosinophilic, homogeneous proteinaceous) casts associated with increased glomerular permeability such as with chronic progressive nephropathy and granular (necrotic cellular debris) casts.