Urine casts: phase contrast

Seven cast types, identifying features, and common look-alikes

Casts form in renal tubules in a uromodulin protein matrix. Identify the matrix first; loose cell clumps can mimic casts.¹

Phase contrast: makes faint structures visible through differences in refractive index. Bright edge halos are optical effects, not extra cast material.^1,2

Photo	Cast and identifying feature	Association and look-alike¹
	Hyaline · 400×Pale matrix with parallel sides; phase contrast makes the faint outline more visible.	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 held 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 overlap; compare nuclei, not size alone.
	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 show Maltese crosses in polarized light.	Lipiduria, often with heavy proteinuria.Look-alike: Starch also forms crosses; confirm droplets within a cast.
	Waxy · 100×Highly refractile, sharply outlined matrix; 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 low power; identify contents at higher power. Delay and dilute alkaline urine can destroy casts; centrifugation can break or lose them. Broad describes width, not contents. Interpret with other urine findings using the laboratory's reporting method.¹

Photos: Bert Grijsen, Microscopic Urine Examination (2026). CC BY-SA 4.0. Cropped; colors unchanged. Magnifications are source values, not print scale.³