Cast in urine is a condition wherein small cylindrical sediments are found in the urine. The condition is also sometimes referred to as ‘urinary casts’. These are cylinder-shaped sediments which are produced by the kidney. These structures are mostly composed of Tamm-Horsfall mucoprotein. Mucoprotein is produced by cells of renal tube and sometimes by the albumin when proteinuria is underlying. The cells that produce these mucoproteins are called epithelial cells. These cells also form lining of distal convoluted tubules and collecting duct system. It is not completely understood what causes precipitation of this mucoprotein causing the condition. It is assumed that pH and concentration of urine may cause such issue. These casts may also occur if the cells are absent in the tubular lumen. During formation of casts if cells are present then they may stick to the get surrounded by network of fibrillar protein.
Types of casts in Urine
Casts in urine can be of different types. There are two categories of casts which can be possibly found in urine which are Acellular casts and cellular casts. Each category has a range of different Casts types which are discussed below:
Acellular casts
Hyaline casts
Hyaline casts is considered as the most common type of casts. In fact these are solidified form of ‘Tamm Horsfall mucoprotein’ which is released by individual nephrons’ tubular epithelial cells. Hyaline casts in urine can be formed because of urine concentration, acidic environment and low urine flow. This is also possible in case of normal person if he is dehydrated or performs vigorous exercise. These casts appear in cylindrical shape and are often clear. They have a low refractive index which makes them sometimes undetectable under brightfield microscopy. Also they can be missed in aged specimen wherein dissolution may have occurred. Phase contrast microscopy test can be used in such a case of easier examination and identification of hyaline sediments.
Granular casts
Granular cast is the second most common type of casts found in urine. This cast forms either due to cellular cast breakdown, immunoglobulin light chains or inclusion of plasma protein aggregates such as albumin. With the size of cellular inclusions it can be determined whether they are harsh or coarse. However, the difference has no importance in diagnosis. These casts are present in cigar-shape and have higher refractive index as compared to hyaline casts. They are common indication of chronic kidney issues. Nevertheless, even strenuous exercise can cause occurrence of such granules in the urine. Muddy brown casts which are detected in case of acute tubular necrosis is an example of granular casts.
Other types of acellular casts include Crystal casts, waxy casts, fatty casts and pigment casts. Crystal casts may include oxalates, sulfonamides or urates which may get enmeshed in ketanaline cast. Waxy casts are considered as end-product of evolution of casts which are associated with serious stage of renal disease or even kidney failure. Fatty casts are produced due to breakdown of epithelial cells that are rich in lipid content. These are yellowish-tan colored hyaline casts that includes fat globule. Pigments casts are often formed due to grouping of metabolic breakdown substances or due to pigments of drugs. These pigments are endogenous products such as hemoglobin, myoglobin, bilirubin, etc
Cellular casts
Red Blood Cell casts
Red blood cells appearing in casts in urine are always due to a medical condition. It may strongly indicate damage to glomerulus. Such damages may occur in case of glomerulonephritis. Subacute bacterial endocarditis or kidney infarction may also contribute to cause the condition. These casts are often cylindrical with ragged corners and appear yellowish-tan in color. Nephritic syndromes or injury to the urinary tract may also cause red blood casts to appear in urine.
White blood cell casts
White blood cell casts are present in urine due to inflammation or infection. These casts are commonly associated with pyelonephritis which is infection of kidney. Inflammatory conditions such as nephrotic disorders, acute interstitial nephritis or even post-streptococcal glomerulonephritis of acute nature can also lead to WBC casts in urine. These casts may be difficult to differentiate from conventional epithelial cells and may need certain staining.
Bacterial casts
Bacterial casts appears with white blood cells as well as WBC casts in conditions such as pyelonephritis. These are loose bacteria casts. This is a rare condition as neutrophils have infection fighting properties.
Epithelial cell casts
Tubule lining of desquamated epithelia cells when sticks together may cause epithelial cell casts in urine. They pattern of adhesion of these cells can be random or in sheet. These are distinguished by large, circular nuclei and decreased degree of cytoplasm.
Casts in urine can be diagnosed through urinalysis. Complete urinalysis comprises of chemical, microscopic and physical evaluation of the urine. To do this the affected individual may have to provide urine specimen collected in a container. Based on urinalysis the doctor may provide instructions to the patient and may onset a treatment if needed.
