[Haematology] Microscopic Examination of Urinary Sediment - ARTIFACTS AND CONTAMINANTS

ARTIFACTS AND CONTAMINANTS, Graff's Textbook of Urinalysis and Body Fluids, Microscopic Examination of Urinary Sediment

Read more: 

1. [Haematology] Microscopic Examination of Urinary Sediment - Cells

2. [Haematology] Microscopic Examination of Urinary Sediment - Crystals
3. [Haematology] Microscopic Examination of Urinary Sediment - CASTS

4. [Haematology] Microscopic Examination of Urinary Sediment - MISCELLANEOUS STRUCTURES

ARTIFACTS AND CONTAMINANTS

A variety of foreign objects can find their way into the urine specimen during collection, transportation, while being tested, or while on the microscope slide. It is important that the technologist be able to recognize these objects as being extraneous structures. 

STARCH CRYSTALS

Starch crystals are frequently found in the urine. They are round or oval, are highly refractive, and vary in size. The most common type of starch which can be present in the urine is cornstarch, possibly because some brands of powder contain cornstarch. Cornstarch crystals are almost hexagonal in shape, and they contain an irregular indentation in the center (Fig. 5-60). Under polarized light these starch crystals will appear as “Maltese crosses” (Fig. 5-61). Anisotropic fat and starch are the only structures that will form these crosses under polarized light. Lycopodium is similar in appearance to cornstarch and is used as a dusting powder.

CLOTH FIBERS

Cloth fibers are undoubtedly the most frequently occurring type of artifact found in the urine. They may come from clothing, diapers, toilet paper, lens paper, or they may be pieces of lint from the air. Fibers which are long and flat are easily recognizable (Fig. 5-62). However, fibers those are short and are approximately the same size as casts can be mistaken for casts.

This error can be avoided by exposing the technologist to the various types of fibers, because there are certain characteristics of the different fibers that can be easily recognized. One way to do this is to take a disposable diaper, cut out a small square, wet the section with water, squeeze it out into a test tube, and examine the sediment (Fig. 5-63). Artifacts of this sort can be seen in sediment that is

Figure 5-60. Starch crystal (500x).

Figure 5-61. Polarized starch crystals. Note the “Mal- tese-cross” formation (400x).

Figure 5-62. Cloth fibers (160x).

Figure 5-63. Fibers. Debris from a diaper. 

This squeezed-out specimen rendered microscopic examination useless. 

Note the various types of fibers present (200x).

obtained by squeezing the urine out of a diaper (a method that should not be practiced). Disposable diapers contain many of the varieties of fibers that appear as contaminants in infant urine specimens.

When observing the different fibers, a few characteristics can be readily noticeable. First of all, they usually have dark edges; casts do not have dark edges. Second, most of the fibers are flat; casts are cylindrical. The fiber in Figure 5-64is frequently encountered in the urine sediment but may be recognized by the thick, nodular edges and the nodular indentations on both ends of the fiber. This fiber is thicker on the edges than in the middle and is usually flat. Refer to the Atlas in Chapter 6 for more pictures of the various fibers.

Figure 5-64. Fiber. This fiber is a common contaminant (400x).

OIL DROPLETS

Oil droplets in the urine are the result of contamination from lubricants. They are spherical and can vary in size (Fig. 5-65)

Figure 5-65. Oil droplet. Field also contains WBCs and squamous epithelial cells (400x)

 

REFERENCES 
Lillian A. Mundt and Kristy Shanahan, Graff's Textbook of Urinalysis and Body Fluids, Second Edition 2011