Thought to represent the end product of cast evolution, waxy casts suggest the very low urine flow associated with severe, longstanding kidney disease such as kidney failure. The "muddy brown cast" seen in acute tubular necrosis is a type of granular cast. While most often indicative of chronic renal disease, these casts, as with hyaline casts, can also be seen for a short time following strenuous exercise. Their appearance is generally more cigar-shaped and of a higher refractive index than hyaline casts. Depending on the size of inclusions, they can be classified as fine or coarse, though the distinction has no diagnostic significance. The second-most common type of cast, granular casts can result either from the breakdown of cellular casts or the inclusion of aggregates of plasma proteins (e.g., albumin) or immunoglobulin light chains. Given the ubiquitous presence of Tamm–Horsfall protein, other cast types are formed via the inclusion or adhesion of other elements to the hyaline base. Hyaline casts are cylindrical and clear, with a low refractive index, so they can easily be missed on cursory review under brightfield microscopy, or in an aged sample where dissolution has occurred whereas, though, phase contrast microscopy leads to easier identification. Low urine flow, concentrated urine, or an acidic environment can contribute to the formation of hyaline casts, and as such, they may be seen in normal individuals in dehydration or vigorous exercise. The most common type of cast, hyaline casts are solidified Tamm–Horsfall mucoprotein secreted from the tubular epithelial cells of individual nephrons. Pyelonephritis or other type of tubulointerstitial inflammationĪcellular casts Hyaline casts. ![]()
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