Urine Sediment of the Month: The Visible Sediment

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After centrifugation of the urine specimen, the macroscopic appearance of the sedimentation can offer certain clues about the nature of the urinary sediment.

Color is by far the most important characteristic to define different sedimentations, but other features such as diffusibility, translucency and adhesiveness have been used. In this post I will consider only the following categories, which can be distinguished rather reliably:

1.  Dark or bright Red (bloody)
2.  Brick-red or Reddish-brown
3.  White
4.  Cloudy

1.  Dark or bright Red (bloody)

Blood in the sediment is usually easily recognized by its dark or bright red color (Fig. 1). Generally, erythrocytes are found at the bottom in mixed sediments.

Fig. 1: Typical sediments in hematuria.

2.  Brick-red or Reddish-brown

A brick colored sediment, the so called sedimentum lateritium (Fig. 2) is typical for high amounts of amorphous urates. Even in much more brownish sediments of urates a reddish-orange hue is readily apparent. Resuspension reveals a grainy structure (Fig. 3).

Fig. 2: A so-called sedimentum lateritium (brick-colored) due to high amounts of
amorphous urates. (Right: Phase contrast, original magnification x100)
Fig. 3: Grainy appearance of amorphous urates upon resuspension.

3.  White

Amorphous phosphates, leucocytes and vaginal fluor can all give rise to predominantly white sediments. Whereas leucocyturia produces a creamy appearance and yellowish tinge (Fig. 4), amorphous phosphates present with bright white coloration (Fig. 5). Vaginal contamination is oftentimes more grayish (Fig. 6).

Fig. 4: A case of pyuria with its typical creamy, yellowish-white sediment. (Right:
Phase contrast, original magnification x400)
Fig. 5: Massive amounts of amorphous phosphates. (Right: Phase contrast,
original magnification x100)
Fig. 6: Grayish-white sediment of vaginal floor.

4.  Cloudy

Mucus can form rather loose, more or less free-floating clouds at the bottom of the tube. (Fig. 7).

Fig. 7: A mucus cloud.

Macroscopic sediment inspection is not rocket science and its clinical relevance is limited. I use it as a quick global assessment of the sediment, to grasp the degree of hematuria and pyuria, and in the differentiation of amorphous phosphates and urates.

Further Reading
Rieder H. Macroscopic characters of sediments. Pages 5-7 in Rieder H, Atlas of urinary sediments. London 1899.

Post by: Florian Buchkremer

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