Casts are clusters of urinary sediment elements (red blood cells, white blood cells, fat bodies, etc.) wrapped in a protein matrix. Cast formation necessarily occurs in the kidney tubules, and the contents of the casts indicate the nature of normal or abnormal occurrences found in the kidney itself.
Granular casts are casts that contain either proteins, tubular cells or leukocytes that have broken down. The presence of granular casts in the urine does not indicate the type of kidney disease present.