Hyaline casts are formed in the absence of cells in the renal tubular lumen. They have a smooth texture and a refractive index very close to that of the surrounding fluid. When present in lower numbers (0-1/LPF) in concentrated urine of otherwise normal patients, hyaline casts are not always indicative of clinically significant disease. Greater numbers of hyaline casts may be seen associated with proteinuria of renal (eg., glomerular disease) or extra-renal (eg., overflow proteinuria as in myeloma) origin.
Fatty casts are identified by the presence of refractile lipid droplets. The background matrix of the cast may be hyaline or granular. Often, they are seen in urines in which free lipid droplets are present as well. Interpretation of the significance of fatty casts should be based on the character of the cast matrix, rather than on the lipid.
Waxy casts have a smooth consistency but are more refractile and therefore easier to see compared to hyaline casts. They commonly have squared off ends, as if brittle and easily broken.
Waxy casts are found especially in chronic renal diseases, and are associated with chronic renal failure; they occur in diabetic nephropathy, malignant hypertension and glomerulonephritis