What is cast that shows up in a urinalysis?

Answer 1

Cast' describes the shape of aggregated particulates in urine rather than a particular substance, thus a modifier is necessary to describe the actual composition of the cast. 'Cast' simply describes a cylindrically shaped aggregation of some particulate that forms in the distal convoluted tubule or distal nephron via precipitation of a mucoprotein secreted by tubule cells (Tamm-Horsfall protein) or, in proteinuria and to a lesser extent, albumin. Cast formation is pronounced in environments favoring protein denaturation and precipitation (low flow, concentrated salts, low pH). Unfortunately, Tamm-Horsfall protein is particularly susceptible to precipitation in these conditions. When present on microscopic evaluation during urinalysis, urinary casts hold significance as diagnostic and prognostic indicators of kidney disease. As reflected in their cylindrical form, casts are generated in the small tubules and collecting ducts of the kidney, and generally maintain their shape and composition as they pass the lower conveyances of the urinary system. Although the commonest forms are benign, other forms are indicative of a pathologic state. All rely on the inclusion or adhesion of various elements on a mucoprotein base - the hyaline cast.