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Casts in urine

Updated on November 19, 2013

Casts in urine refer to tiny, tube-like, cylindrical matter that are made of red blood cells, white blood cells, or kidney cells. They develop in kidney parts known as tubules. Casts are bound together by a protein that is secreted by the kidneys. The different matter occurring in casts in urine can help identify the presence/absence of anomalies in the body.

Some of the different types of casts in urine include hyaline casts, fatty casts, red blood cell casts, granular casts, waxy casts, renal tubular epithelial casts, and white blood cell casts, etc.

Causes of different types of casts in urine

Listed below are some types of casts in urine and its respective causes:

  • Hyaline casts in urine: It is the most prevalent kind of casts in urine. They are crystallized Tamm-Horsfall mucoprotein released by the tubular epithelial cells of each nephron. Concentrated urine, decreased flow of urine, or an acidic setting can trigger the development of hyaline casts. It can also affect healthy people after strenuous exercising or dehydration. Hyaline casts in urine are clear and come with a low refractive index, and can thus be missed during a normal brightfield microscopy. Phase contrast microscopy can however reveal its presence.The other varied casts in urine develop due to attachments of additional elements to a hyaline base structure.

  • Renal tubular epithelial cell casts in urine: Their occurrence indicates mild or extensive tubule cells damage. Epithelial cells casts in urine are found in cases of viral diseases like CMV nephritis, or renal tubular necrosis, and/or ingestion of toxins like diethylene glycol, mercury, or salicylate.Depending on the focus point of injuries, sheets or stacks of cells may simultaneously fall off in each of these health anomalies.Epithelial cell casts develop via adhesion or inclusion of desquamated epithelial cells occurring in the tubule walls. The cells can attach in sheets or in a random manner and can be identified through circular, large nuclei, and decreased quantities of cytoplasm.

  • Granular casts in urine: They can be a symptom of an existing kidney disorder. Granular casts are however generic and can occur in individuals with varied kidney diseases.They can be caused due to the inclusion of plasma proteins or immunoglobulin light chains aggregates, or the breakdown of cellular casts. They have a higher refractive index as opposed to hyaline casts, are typically shaped like cigars, and can be coarse or fine. Even though granular casts in urine are associated with chronic renal disease, it can also result from vigorous exercise.

  • Red blood cell casts in urine: They are a symptom of kidney tubule bleeding. Red blood cell casts can be observed in varied pathologies that affect the glomerulus, such as lupus nephritis, IgA nephropathy, Wegener's granulomatosis and Goodpasture syndrome.They can also have linkages with sub-acute bacterial endocarditis, nephritic syndromes, renal infarctions, and/or urinary tract injuries. The casts are yellowish-brown and are usually tubular along with the occasional ragged borders. It is important to always examine a fresh urine sample for detection of red blood cell casts due to their fragile nature.

  • Fatty casts in urine: They are observed in individuals with urinary lipids, which is typically a nephrotic syndrome complication. Fatty casts form due to breakdown of lipid-abundant epithelial cells which are hyaline casts with a yellowish tan and having fat globule attachments. Additionally, the occurrence of cholesterol or cholesterol esters link fatty casts to ‘Maltese cross’ under polarized light.

  • White blood cell casts in urine: The presence of white blood cells upon or inside the urinary casts can be a symptom of infections or inflammation. White blood cell casts in urine are indicative of pyelonephritis, nephrotic syndrome, acute allergic interstitial nephritis, post-streptococcal acute glomerulonephritis, or parenchymal infection.Special straining methods are needed to differentiate them from epithelial cells.

  • Waxy casts in urine: They are believed to be last in the line of urinary cast evolution. Their occurrence is associated with excessively low flow of urine, different severe kidney diseases, and chronic kidney failure. Waxy casts are considerably larger in size as compared to hyaline casts. This is because of urinary stasis and the growth of waxy casts in dilated and diseased ducts. Waxy casts in urine may also be excessively inflexible, come with a higher refractive index, and elicit fractures, ragged edges, and torn ends.

  • Pigment casts in urine: They develop due to attachment of drug pigments or metabolic breakdown byproducts. Pigment casts in urine can include those released endogenously like myoglobin in rhabdomyolysis, hemoglobin in hemolytic anemia, and bilirubin in liver disease. The name is derived from the discoloration feature elicited by these casts.

Diagnosis of casts in urine is carried out by collecting a midstream/clean-catch sample of urine. A morning urine sample is preferred.

Treatment of casts in urine

  • Treatment of casts in urine is aimed at finding out the underlying cause of the different types of casts, and then treating the pre-existing disease as well as alleviation from the associated symptoms.

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