Urinary cast

Urinary casts are microscopic 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.

[1] As reflected in their cylindrical form, casts are generated in the small distal convoluted tubules and collecting ducts of the kidney, and generally maintain their shape and composition as they pass through the urinary system.

[4] Formed by the breakdown of lipid-rich epithelial cells, these are hyaline casts with fat globule inclusions, yellowish-tan in color.

[citation needed] Formed by the adhesion of metabolic breakdown products or drug pigments, these casts are so named due to their discoloration.

Pigments include those produced endogenously, such as hemoglobin in hemolytic anemia, myoglobin in rhabdomyolysis, and bilirubin in liver disease.

Though crystallized urinary solutes, such as oxalates, urates, or sulfonamides, may become enmeshed within a ketanaline cast during its formation, the clinical significance of this occurrence is not felt to be great.

The presence of red blood cells within the cast is always pathological and is strongly indicative of granulomatosis with polyangiitis, systemic lupus erythematosus, post-streptococcal glomerulonephritis, or Goodpasture's syndrome.

Cells can adhere in random order or in sheets and are distinguished by large, round nuclei and a lower amount of cytoplasm.