Urinalysis and Other Body Fluids, quick reference 6 of 10
06 / 10 · Urinalysis and Other Body Fluids
Urine casts: brightfield
Some photographs show different casts. Compare the identifying features and the effect of the illumination.
Seven cast patterns, 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
Brightfield: transparent casts have little contrast. Reduced illumination helps reveal their outline, and phase contrast can clarify cell detail.1,2
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| Photo | Cast and identifying feature | Association and look-alike1 |
|---|---|---|
| Hyaline · 400× Pale matrix with parallel sides. Faint edges can disappear in strong illumination. | 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× Granular white cells in a matrix. Nuclear lobes may be difficult to resolve. | Renal inflammation, including pyelonephritis and interstitial nephritis. Look-alike: Tubular cells or white cell clumps can resemble a cast. | |
| Epithelial / white cell · 400× The source labels this as an epithelial/white-cell cast. Indistinct nuclei limit cell typing. | Tubular injury or renal inflammation. The cast alone cannot establish the cause. 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 · 400× 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