casts and crystals in urine
Micrograph showing casts in a kidney biopsy using PAS stain. Hyaline casts are PAS-positive (dark pink/red, right of image). Myelomatous casts are PAS-negative (pale pink, left of image) Urinary casts are cylindrical structures produced by the kidney and present in the urine in certain disease states. They form in the distal convoluted tubule and collecting ducts of nephrons, then dislodge and pass into the urine, where they can be detected by microscopy.
These solutes can form crystals, solid forms of a particular substance, in the urine if: 1  The urine pH is increasingly acidic or basic; 2  The concentration of dissolved substances is increased; and. 3  The urine temperature promotes their formation.