Urinary casts are held together by the Tamm-Horsfall mucoprotein which is secreted by renal tubule cells, and sometimes also by albumin in conditions of proteinuria. Cast formation is pronounced in environments favoring protein denaturation and precipitation. Tamm-Horsfall protein is particularly susceptible to precipitation in these conditions.
Types of urinary casts include: 1) hyaline casts, which are cylindrical and clear, with a low refractive index and can be seen in normal individuals in dehydration states or after vigorous exercises; 2) granular casts, which result either from the breakdown of cellular casts or the inclusion of aggregates of plasma proteins and they are a sign of chronic renal disease; 3) fatty casts, which are formed by the breakdown of lipid-rich epithelial cells and may be present in various renal disorders, such as the high urinary protein nephrotic syndrome; 4) waxy casts, which are associated with severe, longstanding kidney disease such as renal failure; 5) epithelial casts, which are formed by adhesion of desquamated epithelial cells of the tubule lining and can be seen in acute tubular necrosis and toxic ingestion, such as from mercury, diethylene glycol, or salicylate; 6) red blood cell casts.
Types of Urinary Casts