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.