Urinalysis and Other Body Fluids, quick reference 5 of 10
05 / 10 · Urinalysis and Other Body Fluids
Urine casts: phase contrast
Some photographs show different casts. Compare the identifying features and the effect of the illumination.
Seven cast types, identifying features, and common look-alikes
Casts form in renal tubules in a uromodulin protein matrix. Identify the matrix first, because loose cell clumps can mimic casts.1
Phase contrast makes faint structures visible through differences in refractive index. Bright edge halos are optical effects and do not belong to the cast.1,2
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| Photo | Cast and identifying feature | Association and look-alike1 |
|---|---|---|
| Hyaline · 400× Pale matrix with parallel sides. Phase contrast makes the faint outline easier to see. | Concentrated urine, exercise, or renal disease. A few may occur without disease. Look-alike: Mucus tapers and varies in width. | |
| Red cell · 400× Red cells within a continuous matrix. | Bleeding within the nephron, especially from a glomerular source. Look-alike: Free red cell clumps have no enclosing cast matrix. | |
| White cell · 400× White cells in a matrix. Look for granular cytoplasm and lobed nuclei. | Renal inflammation, including pyelonephritis and interstitial nephritis. Look-alike: Tubular cells or white cell clumps can resemble a cast. | |
| Tubular epithelial · 400× Tubular cells with single round nuclei and visible cytoplasm within a matrix. | Tubular injury. Degeneration can obscure the cell type. Look-alike: White cell and tubular cell casts can look alike. Compare the nuclei, because size alone cannot separate them. | |
| Granular · 400× Coarse or fine granules fill the matrix as cells and proteins break down. | Numerous muddy brown casts support tubular injury. A few granular casts are less specific. Look-alike: Debris or crystal clumps lack a continuous cast outline. | |
| Fatty · 400× Refractile lipid droplets within a matrix. Some droplets show Maltese crosses in polarized light. | Lipiduria, often with heavy proteinuria. Look-alike: Starch granules also form crosses. Confirm that the droplets lie within a cast. | |
| Waxy · 100× Highly refractile, sharply outlined matrix with cracks, notches, and blunt ends. | Prolonged tubular stasis, often with advanced renal impairment. Look-alike: Fibers have irregular edges and lack a cast matrix. |
Scan at low power, then identify contents at higher power. Examine fresh urine, because delay and dilute alkaline urine can destroy casts.1