Page 386 - The Veterinary Laboratory and Field Manual 3rd Edition

Clinical chemistry 355

Pus cells (white cells) may also be found in urine (urolithiasis) can be more severe in cases
urine sediment (pyuria), these are predomi- of bladder damage with associated infection
nantly polymorph leukocytes (neutrophils) (cystitis) and changes in urine pH.
which have migrated from the blood. They have Spermatozoa are often found in urine and
a nucleus with several segments. As pus cells are this is quite normal in male, or recently mated
broken down and destroyed in the urine, their or inseminated female animals. Trichomonas pro-
nuclei may disappear and only the cell mem- tozoa can be seen in urine contaminated with
branes remain. A few pus cells are often found in preputial or vaginal discharges from infected
free-caught urine samples from healthy animals. animals. If there are any motile protozoa in the
Because of this, it is usual to take a number urine, they are almost certainly Trichomonas sp.
below which it is said to be normal, and above Microorganisms are frequently seen in free-
which it is said to be abnormal. Ten pus cells caught urine. Bacteria found in samples taken by
per microlitre is a common figure to take. Less cystocentesis or catheterization are more likely
than 10 pus cells per microlitre are thought to to be significant. Like all very small things, bac-
be normal. More than 10 pus cells per microli- teria are only seen clearly in stained preparations
tre are thought to be abnormal and to indicate a examined microscopically using a high power or
urinary tract infection. This is only a guide, but oil immersion objective. Many urinary bacteria
it is a useful one. are motile. Bacteria often grow in urine if it is
Epithelial cells are large flat cells with a left to stand in a warm room and commonly
nucleus that can usually be seen quite easily. get into the sample from a dirty container or as
They come from the epithelium on the inside of contaminants from the skin. Finding bacteria in
the ureters, bladder and urethra. Epithelial cells old urine therefore means little. When signifi-
are usually single but sheets of several epithelial cant bacteria are seen in fresh urine there will
cells are sometimes seen. Sometimes epithelial usually also be pus cells and protein present to
cells are found in normal urine, but if present indicate inflammation. In some samples, there
along with large numbers of red blood cells and may be yeasts or the mycelia of fungi (these are
pus cells this is abnormal and indicates damage longer and thicker than a bacterium, and they
to the urinary tract. branch). Some objects in urine debris may not
When urine is formed in the kidney all the be significant but it is important to be familiar
chemicals in it are in solution. After it has with their appearance, for example, a small bub-
left the kidney, some of these chemicals may ble of air, bits of debris, pieces of cotton thread
form a urinary deposit. Sometimes they form and scratches on the slides are commonly seen
small solid granules without any special shape. (Figure 7.13).
Deposits of this kind are said to be amorphous
(without shape). These deposits are very com-
mon. Often, however, these chemicals, as they 7.10 Toxicology
become solid, take on the shape of crystals.
When seen from above some crystals are square Judit E Smits
with a cross on them like an envelope. These There are a wide range of natural and man-made
are oxalate crystals. Other kinds of crystal are compounds that are potentially toxic to animals.
shown in Figure 7.13. The shape of the crystals Numerous types of plants, toxins produced by
often tells us what they are made of, but crystals algae, and fungi that contaminate grain are
in the urine are seldom significant unless they among the naturally occurring elements that can
irritate the bladder lining. Crystal formation in affect livestock and domestic animals. Generally,

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