Internally reviewed Because Tamm-Horsfall protein is a globulin, the reagent strip analysis of the urine does not detect this protein. As the urine in the tubules becomes concentrated, as urine stasis occurs or when the pH is very low, the protein forms fibrils that attach to the lumen cells. The fibrils intertwine to eventually form the cast itself which is washed out into the urine as flow increases. While the fibrils intertwine, they may entrap other chemicals or elements that are present in the urine.
Casts vary in length and thickness, but the diameter is uniform throughout the length of each cast.
The sides are parallel and the ends are rounded in the unbroken structures. The cylindrical shape of casts is shown by their rolling effect when the urine under the cover slip moves. The refractive index of casts, especially hyaline casts, is similar to that of the urine itself. For this reason they are frequently difficult to see and very subdued light is required. Hyaline are the least significant of the casts and a few can be found in the urine of normal individuals after physical exertion, emotional stress or febrile diseases.