urinary cast

Pathology

• urinary casts are formed only in the distal convoluted tubule or the collecting duct
• translucent colorless gels formed from proteins in the tubules of nephrons
• very few casts are seen in the urine sediment of healthly individuals, except after heavy exercise (proteinuria of heavy exercise)
• increased numbers of casts generally indicate renal disease involving many nephrons
• the Tamm-Horsfall protein forms the matrix of all casts, forming a meshwork of fibrils that trap cells, cell fragments or granular material
• plasma proteins entering the tubules (generally albumin but also hemoglobin, myoglobin or immunoglobulin light chains) increase cast formation combining with Tamm-Horsfall protein to form less lucent casts & granular casts
• cast formation increases with diminished pH, increased ionic strength & with stasis of urine within the nephron
• casts begin to disintegrate in dilute or alkaline urine or in the presence of bacteria (possibly via alkalinization)

Indications

• evaluation of proteinuria

Clinical significance

• erythrocyte casts are seen with glomerular disease (glomerulonephritis)
• leukocyte casts indicate inflammation of the renal parenchyma (pyelonephritis or acute interstitial nephritis)
• granular casts (muddy brown casts) are seen with acute tubular necrosis
• broad casts are associated with chronic kidney disease

More general terms

• abnormal morphologic structure (malformation)

More specific terms

• broad cast
• broad, muddy brown cast
• epithelial cast
• erythrocyte cast (RBC cast)
• fatty cast
• granular cast
• hemoglobin cast
• hyaline cast
• leukocyte cast (WBC cast)
• mixed cellular cast
• myoglobin casts in urine
• pseudocast
• waxy cast

Component of

• urinalysis (UA)