Urinary casts

Alternative names:

casts in the urine; epithelial casts; fatty casts; granular casts; hyaline cast; renal tubular casts; waxy casts

What the risks are:

There are no risks.

Special considerations:

Casts are reported as part of the normal microscopic examination of urinary sediment (that is, the material that gets centrifuged to the bottom of the tube). Casts are formed as translucent, colorless gels from protein in the tubules of nephrons. In normal urine there is a very small amount of protein, less than 150 mg/day. Urine albumin and small globulins derived from plasma comprise two-thirds of the protein in urine. The other one-third is comprised of Tamm-Horsfall protein, a glycoprotein that is secreted by renal tubular cells. It is thought that Tamm-Horsfall protein forms the matrix of all casts (although other proteins can subsequently contribute). Under certain conditions, this protein forms a meshwork of fibrils that can trap cells, cell fragments, or granular material. Cast formation increases with lower pH and where there is stasis (decreased flow of urinary filtrate) or obstruction of the nephron by cells or cell debris. Casts begin to disintegrate in dilute and alkaline urine or in the presence of bacteria, which probably contribute to a decreasing acidity. The size and shape of casts depends on the site of formation. Large casts are seen in dilated tubules or with stasis in collecting ducts. Thin casts occur in tubules compressed by swollen interstitial tissue or because of disintegration.

Note: mg/day = milligrams per day