Hyaline Casts

Hyaline Casts

Hyaline casts are formed in the absence of cells in the tubular lumen. They consist of Tamm-Horsfall protein and have a smooth texture and a refractive index very close to that of the surrounding fluid. They are very difficult to see in wet preparations of urine and must be distinguished from mucus strands. Generally\, hyaline casts have parallel sides with clear margins and blunted ends, whereas mucus strands are irregular in size with irregular margins. Reduced lighting is essential to see hyaline casts in urine sediment preparations. They are easier to see if you lower the substage condenser and if other particles (fat, debris) are caught up within them (see image on the left below). Hyaline casts are far easier to visualize using phase contrast microscopy (see image on the right below), but this is not available on standard microscopes.


Hyaline casts (outlined by black arrows) in a wet preparation of urine sediment as visualized with the condenser racked down.	Hyaline casts (indicated by the black arrow) as seen under phase contrast microscopy. The edges of the cast are easier to see with this technique.

Hyaline casts can be present in low numbers (0-1/LPF) in concentrated urine of otherwise normal patients and are not always associated with renal disease.

Greater numbers of hyaline casts may be seen in association with proteinuria of renal (e.g., glomerular disease) or extra-renal (e.g., overflow proteinuria as in myeloma) origin. In such cases it has been proposed that the presence of excessive serum protein in the tubular lumen promotes precipitation of the Tamm-Horsefall mucoprotein.