Leukocyte cast
Synonyms: Pus casts
Casts are elongated structures formed in the renal tubules and composed mainly of uromodulin, also known as Tamm-Horsfall protein. This glycoprotein is secreted by cells in the ascending Lis of Henle and the distal tubule segment. The formation of casts is promoted by acidic pH and concentrated urine, conditions that allow the precipitation of uromodulin in a gel-like structure. During their formation, casts can enclose other components from the tubular fluid, such as cells, fat droplets or granular (granular) debris, creating different types of casts. In a sense, therefore, a cast can be considered a "biopsy" of the part of the tubule in which it is formed. Casts are visible microscopically, usually under bright-field microscopy, but their detection depends on their composition and transparency.
Leukocyte casts may contain varying amounts of white blood cells, ranging from few to fully loaded. When the cells are degraded, they may be difficult to distinguish from renal tubular epithelial cells. In such cases, they are referred to as cell casts. Leukocyte casts are characteristic of acute bacterial infection involving the kidney, such as pyelonephritis. However, they can also be observed in active, proliferative lupus nephritis, other glomerular diseases or acute interstitial nephritis.
