Urine Sediment of the Month: 4 Flavors of Nucleated Cells

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In the routine urinary sediment examination, you may come across 4 types of nucleated cells:

1. Squamous epithelial cells
2. Leukocytes
3. Transitional epithelial cells
4. Tubular epithelial cells

Let’s discuss how to differentiate between them.

Squamous epithelial cells are easily identified by their huge size and polygonal shape (Fig. 1 and 2). They signify contamination of the urine with vaginal or urethral content.

Figure 1. Squamous epithelial cells, low power view. (Phase contrast, original magnification x100).
Figure 2. Squamous epithelial cell, high power view. (Phase contrast, original magnification x400).

Leukocytes, a sign of kidney or urinary tract inflammation, are much smaller and show an overall granular texture (Fig. 3). Polymorphonuclear cells with typical lobulated nuclei are most common (Fig.4).

Figure 3. Leukocytes (blue arrow) are much smaller than squamous epithelial cells (black arrow). Superficial urothelial cells (yellow arrow) lie in between. (Phase contrast, bright field, original magnification x400).
Figure 4. Densely packed leukocytes in a patient with urinary tract infection. (Phase contrast, original magnification x400).

Transitional epithelial (or urothelial) cells come in various shapes. Superficial cells resemble fried eggs with large, round nuclei and relevant amounts of cytoplasm (Fig. 5). Cells from the deeper layers have much less cytoplasm and often tails or pointed cellular extensions (Fig. 6).

Figure 5. Superficial urothelial cells. (Phase contrast, bright field, original magnification x400).
Figure 6. Urothelial or transitional cells from the superficial or deep layers. (Phase contrast, original magnification x400).

Tubular epithelial cells are an important sign of tubular damage (for oval fat bodies see here). They also have round nuclei and sparse amounts of cytoplasm (Fig. 7 and 8).

Figure 7. Tubular epithelial cells in a patient with acute kidney injury. (Phase contrast, original magnification x400).
Figure 8. Tubular epithelial cells in a patient with AKI 3. (Bright field, original magnification x400).

There are two ways to ensure the tubular origin of these cells:

1. Find morphologically identical cells within casts (Fig. 9).
2. Find pigmented inclusions within the cells (Fig. 10 & 11).

Figure 9. Tubular epithelial cells, free and within a cast. Patient with AKI 3. (Phase contrast, bright field, original magnification x400).
Figure 10. Intracytoplasmic pigmented granules are a great clue to identify tubular epithelial cells. (Bright field, original magnification x400)
Figure 11. Intracytoplasmic pigmented granules are a great clue to identify tubular epithelial cells. (Bright field, original magnification x400)

Without these findings, it is often times impossible to reliably distinguish tubular epithelial cells from deep-layer transitional cells by morphology alone. Considering the sediment background can help: In a sediment with extensive muddy brown casts for example, small epithelial cells with round nuclei are usually of tubular origin. In a case with heavy leukocyturia and detectable superficial urothelial cells, they probably represent transitional cells.

All cellular elements in the urinary sediment are prone to degenerative changes caused by osmotic stresses and/or cellular death or dying. You should resist trying to force identification, not every cell can be reliably classified!

Post by: Florian Buchkremer

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