Casts in Urine

The occurrence of tiny, cylindrical, tube-like structures in urine is known as casts in urine. Such matter consists of WBCs, RBCs, or kidney cells and form in sections of kidneys referred to as tubules. A protein produced by the kidneys help bind together the casts. Doctors will examine the varied substances present in casts in urine to diagnose the underlying causative conditions, if any.

Causes and Types of Casts in Urine

casts in urine

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The different kinds of casts that occur in urine are hyaline casts, red blood cell casts, fatty casts, granular casts, renal tubular epithelial casts, waxy casts, and white blood cell casts.They are caused due to:

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  • Hyaline casts: These casts in urine are crystals of Tamm-Horsfall mucoprotein that are secreted by each nephron’s epithelial cells. Hyaline casts are transparent with low refractive index. Hence, it is possible to miss their detection during a brightfield microscopy. However, they can be easily detected via a phase contrast microscopy.
    • Hyaline casts in urine can form due to triggers such as reduced urine outflow, increased urine concentration, or acidic environments.Healthy individuals may also experience hyaline casts in urine when dehydrated or post vigorous workouts.
    • Note: The addition of more elements to a base structure of hyaline casts in urine usually develop into the other different casts.
  • RBC casts: Red blood cells casts in urine are usually a sign of bleeding in kidney tubules as well as varied conditions affecting the glomerulus like IgA nephropathy, lupus nephritis, Goodpasture syndrome, and Wegener’s granulomatosis, etc. It is also known to be associated with urinary tract trauma or injuries and/or pathologies like nephritic syndromes, sub-acute bacterial endocarditis, and renal infarctions, etc.
    • RBC casts in urine are usually yellowish brown in color and tubular. Sometimes, the borders may be uneven. These casts are very delicate and hence all relevant tests are carried out on a fresh urine specimen.
  • WBC casts: In this, the white blood cells may occur within or on the casts in urine. In most cases, it usually signifies inflammation or infection. Some conditions associated with WBC casts in urine include nephrotic syndrome, pyelonephritis, acute allergic interstitial nephritis, parenchymal infection, and/or post-streptococcal acute glomerulonephritis, etc.Lab technicians make use of special straining options to isolate such casts from the epithelial cells.
  • Granular casts: These casts in urine may develop due to degradation of cellular casts or attachment of aggregates of immunoglobulin light chains or plasma proteins. Granular casts are normally generic and may be a sign of some underlying kidney disease.They can be fine or coarse and often tubular in shape. In comparison to hyaline casts, they feature a higher refractive index. In addition to different kinds of chronic renal diseases, granular casts can also occur due to strenuous workouts.
  • Renal tubular epithelial cell casts: These casts in urine are often a symptom of minor or serious damage of the tubule cells. They may occur due to ingestion of poisons such as mercury, diethylene glycol, or salicylate, or due to underlying viral illnesses like renal tubular necrosis or CMV nephritis.In each of these medical problems and as per the center point of causative trauma, stacks or sheets of epithelial cells may drop off simultaneously. The cells casts may form due to inclusion or attachment of the tubule walls’ desquamated epithelial cells. The epithelial cells tend to join randomly or in sheets and can be isolated via large, circular nuclei and reduced cytoplasm levels.
  • Fatty casts: These casts in urine occur due to disintegration of lipid-rich epithelial cells which are nothing but yellowish tanned hyaline casts with attachments of fat globules. Fatty casts typically affect patients with urinary lipids, which in turn is often a complication of nephrotic syndrome.
  • Pigment casts: These casts in urine occur due to drug pigments attachment or attachment of metabolic degradation of byproducts. They may consist of endogenously secreted pigments such as myoglobin in rhabdomyolysis; bilirubin in liver diseases; and hemoglobin in hemolytic anemia. The casts are usually discolored and hence the name.
  • Waxy casts: These casts in urine are regarded as the last stage of evolution of urinary casts. They may be symptomatic of varied serious kidney diseases, severely low urine output, and/or chronic kidney failure.Urinary stasis and development of the casts in diseased and dilated ducts causes them to be much bigger than hyaline casts. Waxy casts tend to be more rigid and less flexible; may be fractured; feature high refractive index; and may have torn tips and/or uneven borders.

Treatment of casts in urine

As discussed above, casts in urine are caused due to different kinds of diseases. Hence, doctors need to first diagnose the type of casts present in urine and the underlying ailment. Once it is detected, then treatment proceeds as per the standard therapeutic procedures. Medications, lifestyle changes, etc. may help cure not just the underlying illness, but will also help alleviate the additional symptoms that may accompany a case of casts in urine.


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