They are a yellowish-brown color and are generally cylindrical with sometimes ragged edges; their fragility makes inspection of a fresh sample necessary. They are usually associated with nephritic syndromes or urinary tract injury. White blood cell casts
Indicative of inflammation or infection, the presence of white blood cells within or upon casts strongly suggests pyelonephritis, a direct infection of the kidney. They may also be seen in inflammatory states, such as acute allergic interstitial nephritis, nephrotic syndrome, or post-streptococcal acute glomerulonephritis. White cells sometimes can be difficult to discern from epithelial cells and may require special staining. Differentiation from simple clumps of white cells can be made by the presence of hyaline matrix. Bacterial casts
Given their appearance in pyelonephritis, these should be seen in association with loose bacteria, white blood cells, and white blood cell casts. Their discovery is likely rare, due to the infection-fighting efficiency of neutrophils and the possibility of misidentification as a fine granular cast. Epithelial cell casts
This cast is formed by inclusion or adhesion of desquamated epithelial cells of the tubule lining. Cells can adhere in random order or in sheets and are distinguished by large, round nuclei and a lower amount of cytoplasm. These can be seen in acute tubular necrosis and toxic ingestion, such as from mercury, diethylene glycol, or salicylate. In each case, clumps or sheets of cells may slough off simultaneously, depending on the focality of injury. Cytomegalovirus and viral hepatitis are organisms that can cause epithelial cell death as well. Eosinophilic cast
This type of cast contains eosinophils.
They are more rigid, demonstrating sharp edges, fractures, and broken-off ends.Waxy casts are broad casts, which is a more general term to describe the wider cast product of a dilated duct. It is seen in chronic kidney failure. In nephrotic syndrome many additional types of cast exist including broad and waxy casts if the condition is chronic (this is referred to as a telescopic urine with the presence of many casts). Fatty casts
Formed by the breakdown of lipid-rich epithelial cells, these are hyaline casts with fat globule inclusions, yellowish-tan in color. If cholesterol or cholesterol esters are present, they are associated with the "Maltese cross" sign under polarized light. They are pathognomonic for high urinary protein nephrotic syndrome. Pigment casts
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. Drug pigments, such as phenazopyridine, may also cause cast discoloration. Crystal casts
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. Cellular casts
Red blood cell casts
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 Goodpastures syndrome. They can also be associated with renal infarction and subacute bacterial endocarditis.