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 the abnormalities occurring in the kidney itself.
Waxy casts probably represent the last stage of granular cast degeneration. Waxy casts are non-specific and can be observed in a wide variety of acute and chronic kidney diseases. However, they indicate a certain degree of slowing in urine formation and, therefore, possibly more advanced kidney disease.