Fatty Casts

Fatty casts are urinary casts formed by the breakdown of lipid-rich epithelial cells, these are hyaline casts with fat globule inclusions, yellowish-tan in color. If cholesterol or cholesterol esters are present, fatty casts are associated with the “Maltese cross” sign under polarized light. They can be present in various disorders, including the high urinary protein nephrotic syndrome, diabetic or lupus nephropathy, or larger-scale necrosis or epithelial cell death.

Fatty casts are identified by the presence of refractile lipid droplets. The background matrix of the cast may be hyaline or granular in nature. Often, they are seen in urines in which free lipid droplets are present as well. Fatty casts are the most common type seen in cat urines. Interpretation of the significance of "fatty" casts should be based on the character of the cast matrix, rather than on the lipid content.

Fatty Casts