Page 357 - The Veterinary Laboratory and Field Manual 3rd Edition

chapter 7

Clinical chemistry

Susan C. Cork, Willy Schauwers and Roy Halliwell

7.1 Introduction urea nitrogen levels, urine protein, urine or
blood glucose, pH and so on). More specialized
The discipline of clinical chemistry includes the tests for toxicology and for endocrine assays are
biochemical analysis of serum and/or plasma, often only done in specialized referral centres. If
urine and other body fluids (for example, cere- you are likely to send samples to these reference
brospinal fluid, transudates and so on). In this centres you will need to be familiar with spe-
chapter, we will outline some of the common cific postal regulations for transporting clinical/
tests used for disease diagnosis with brief ref- pathological specimens in the standard post (see
erence to toxicological tests and endocrine Chapters 1 and 8).
studies. Most district veterinary laboratories are
only able to perform basic biochemical tests on
serum/plasma, and body fluids and urinalysis. In 7.2 Blood sample collection and
larger laboratories, automated blood biochemis- handling
try systems may be available that can be used to
perform a range of biochemical profiles on whole Most biochemical assays performed require
blood or serum plasma from common domes- serum from clotted blood (that is, collect
tic species, but these systems can be expensive samples using a red topped vacutainer) but
to run. Commercial diagnostic laboratories and for some tests, plasma from heparinized blood
some private veterinary clinics commonly use (that is, a green topped vacutainer) or blood col-
automated blood chemistry systems but cost lected in calcium oxalate (that is, a grey topped
recovery requires a minimal turnover of samples. vacutainer) is preferable, that is, for glucose
These will not be considered in detail here. The assessment. Blood collected in EDTA tubes
samples required for biochemical tests depend (purple topped) is generally used for haematol-
on what tests are to be performed. ogy (see Chapter 5). Plasma may be collected
District laboratories are not usually equipped from EDTA samples but these are not the first
for comprehensive quantitative clinical pathol- choice for biochemistry tests because the antico-
ogy although semi-quantitative and simple agulant may interfere with the test. In general,
qualitative tests may be possible Fouchet’s test 2 ml of serum or plasma is the minimum volume
to detect bilirubin in urine or the ‘dip-stick’ kit required (that is, from > 5 ml blood collected).
tests which rely on simple chemical reactions This volume allows re-testing if necessary and
which change the colours of reagent(s) in the also makes it possible to perform additional tests
strips (that is, as seen in reagent strips for blood where indicated. Where possible, the submit-

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