<P> 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 . </P> <P> 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 . </P> <P> 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 . They can also be associated with renal infarction and subacute bacterial endocarditis . 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 . </P> <P> 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 . </P>

Red blood cell casts in the urine always indicate
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