Urinary cast

Urinary Cast

Urinary cast (/ˈjʊərɪnəri kæst/; from the Latin urina, meaning "urine", and the Old Norse kasta, meaning "to throw") are cylindrical structures produced by the kidney and present in the urine in certain disease states. They form in the distal convoluted tubule and/or the collecting duct and take the shape of the lumen of the tubule (tubular lumen).

Urinary casts are the result of protein precipitation, which can occur due to low flow rates, high salt concentration, and a low pH, conditions that commonly occur in the distal convoluted tubule. They are usually associated with various types of nephropathy (kidney diseases), including glomerulonephritis and acute tubular necrosis.

Types of Urinary Casts

There are several types of urinary casts, each associated with different conditions:

Hyaline casts are composed of a mucoprotein (Tamm-Horsfall protein) secreted by tubule cells. They are often seen in normal urine.
Red blood cell casts are indicative of glomerulonephritis, with leakage of RBCs from glomeruli, or severe tubular damage.
White blood cell casts are indicative of inflammation of the kidney, because WBCs are associated with inflammation.
Granular casts are a sign of tubular damage. They are likely the most common type of cast seen in urinary sediment.
Waxy casts are indicative of chronic renal disease. They are the final stage of degeneration of cellular casts, and can be associated with chronic kidney disease.

Clinical Significance

The presence of urinary casts is often a sign of kidney disease. The type of cast found can provide clues to the type of kidney disease present and may guide further diagnostic testing. For example, red blood cell casts are associated with glomerulonephritis, while white blood cell casts may indicate acute pyelonephritis or interstitial nephritis.