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Clinical chemistry 351

7.8 Mineral and trace element assays sample of a known concentration. Assays for tis-
sue trace element or mineral levels are usually
For the interpretation of mineral and trace ele- more specialized and would be done on samples
ment assays it is important to also consider the of liver and other tissues collected at necropsy
general health status of the animals tested, for or from a biopsy collected by a consulting
example, a cow with liver disease may release veterinarian.
a lot of stored copper into the blood stream It should be noted that for trace elements
resulting in artificially elevated levels of copper that are co-factors, or chemical mediators, in
in the serum. There is usually a combination of essential biochemical processes, the chemical
factors that contribute to dietary deficiencies measured in the blood may be a specific enzyme
(for example, poor nutrient intake, concurrent or substance as opposed to the element itself, for
disease, debility) but the adequacy of the diet is example, vitamin B for cobalt (Co) and gluta-
12

often the first thing to consider. In cases where thione peroxidase for selenium (Se).
several animals develop specific nutrient defi-
ciencies it is especially important to assess the
diet. This may involve analysis of commercial 7.9 Urinalysis
feed (for example, for energy, protein, minerals
and trace elements) or assessment of the veg- Urinalysis is the examination of urine and can
etation and soil in the area the livestock graze. provide information about the general health of
Due to potential interactions between nutrients an animal as well as the urinary tract. The uri-
and also variation in the uptake of trace element nary tract consists of the kidneys (which make
and other dietary components it can take time to urine while filtering the blood) the ureters (the
determine the cause of a deficiency. For example, tubes joining the kidneys to the bladder), the
if pasture or soil is high in one trace element bladder (the bag which holds the urine) and
(for example, molybdenum, Mo) it may interfere the urethra (the tube which joins the bladder
with the uptake of others (for example, copper, to the outside). In most cases a fresh midstream
Cu). Low values of Ca/P may indicate inadequate specimen of urine is suitable but for some tests
feed but may also be associated with parturition it is necessary to collect a sample aseptically by
and heavy lactation stress (for example, milk catheterization or cystocentesis (that is, collect-
fever), for these reasons any samples sent for ing by syringe directly from the bladder during
trace element assessment should be submitted anaesthesia for microbiological examination). It
along with a full clinical history. Because serum is important to get a ‘representative’ specimen of
levels of Ca and P are highly inter-linked physi- urine that reflects the state of the urine as it is in
ologically, sera should be tested for both Ca and the bladder, that is, without any contamination
P concurrently and the results assessed together. from the vagina or urethra, skin, environment or
There are a range of commercial assays container. Although the risk of sample contami-
available for serum mineral and trace element nation can be reduced by inserting a catheter into
assessment, most are based on colorimetry and the bladder, but this can be dangerous for the
are fairly easy to perform. Commercial kit tests animal because bacteria may enter the bladder on
(for example, QuantiChrom , Magnesium the catheter and infect the urinary tract. Smears
TM
and Copper Assay Kits, BioVision Calcium can be prepared (on a glass slide) from any sedi-
Colorimetric Assay Kit) come with detailed ment present in the sample, these are stained
instructions and usually provide example cal- and examined under the microscope for the
culations based on comparison with a standard presence of any cellular material. On standing,

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