Hyaline casts consist of only the Tamm-Horsfall protein matrix. A few hyaline casts (0-2/low power field) are considered normal. They may be visible in the urine sediment, if the individual has been exercising heavily, has a fever; or is undergoing diuretic therapy.
Pathologically, hyaline casts may be seen with congestive heart failure, and may be seen together with other types of casts in a variety of renal diseases.
Hyaline casts are generally translucent and homogeneous, but may contain a few granules within the matrix. Hyaline casts have a refractive index similar to urine, and are easily missed. Visualization of these casts is enhanced by using subdued light or by using phase-contrast microscopy.
Formation of hyaline casts between the juncture of the ascending loop of Henle and the distal convoluted tubule may result in a cylindroid (tail) appearance at one end.