Urine Sediment of the Month: Findings in Cirrhosis, Cholestasis, and Hyperbilirubinuria

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Microscopic examination of the urinary sediment in the context of hyperbilirubinemia and increased urinary bilirubin excretion requires special attention to the unique chromatic characteristics acquired by the specimens. As serum bilirubin increases, a yellow-tinged urine becomes increasingly noticeable. This is notorious in patients with serum total bilirubin approximately greater than  20 – 30 mg/dL.

Cirrhosis, obstructive or drug-induced cholestasis, and alcoholic hepatitis represent the most important categories of patients with this feature. When patients with those entities present with acute kidney injury (AKI), careful inspection of the urinary sediment is required to assess for evidence of acute tubular injury or other parenchymal cause of AKI. Urine sediment can help make a diagnosis of hepatorenal syndrome type 1 or entertain others such as cholemic nephrosis.

Figure 1. Magnified high-power view of bilirubin-stained hyaline casts under bright field microscopy (A,B) and bilirubin-stained finely granular casts under bright field (C) or phase contrast (D) microscopy.
Figure 2. Bilirubin-stained casts indicative of acute tubular injury under bright field microscopy: (A) abundant coarse and muddy brown granular casts at low-power field clustered at the edge of the coverslip. (B) coarse granular cast at magnified high-power field (m-HPF). (C) muddy brown granular cast at m-HPF. (D) waxy cast at m-HPF.

Because of staining by bilirubin, hyaline casts may become more apparent (Figure 1) and granular and waxy casts may have various degrees of color intensity (Figures 1, 2). Use of Sternheimer-Malbin (SM) stain is usually not necessary in this context, but when it is used, the mixture of bilirubin and the violet color of SM stain creates a distinct orange/maroon color.

Figure 3. Bilirubin-stained renal tubular epithelial cell casts (RTECC) under bright field microscopy. (A) abundant RTECC at low-power field. (B,C) RTECC at magnified high-power field (m-HPF). (D) Sternheimer-Malbin-stained RTECC at m-HPF.

In patients with markedly elevated total bilirubin, renal tubular epithelial cells are a common finding (Figure 3), whereas leucine and bilirubin crystals can be identified only occasionally (Figure 4).

Figure 4. High-power view of urinary crystals observed in severe hyperbilirubinemia: Leucine crystals (A) isolated under bright field microscopy, (B) within hyaline casts under phase contrast microscopy and (C) under polarized light. (D) bilirubin crystals under bright field microscopy (specimen from a patient with a serum bilirubin of 62 mg/dL).

By Juan Carlos Velez @VelezNephHepato

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