General screening for subclinical and some clinical entities in elite equine athletes is often undertaken using a battery or package of tests that are chosen
by the laboratory or by the individual clinician. Low-grade abnormalities or significant clinical entities can then be further investigated, by study of specific organ systems e.g. liver, kidney, GIT etc. This approach has much to recommend it, but it is important
to remember that the statistical probability of having one or more values outside a reference range increases can increase with the number of tests carried out, regardless of the presence of disease or other compromise. Reference ranges for frequently used biochemical tests such as total protein and globulin can be based on selection of horses with normal WBC and plasma fibrinogen values.
Sample collection: Blood samples must be collected into the appropriate containers. Collection into evacuated containers has become the norm. Potassium EDTA is the anticoagulant for haematology. Lithium heparin is not suitable for this purpose, because it does not permit differential white cell counting. Samples for blood biochemistry testing can be collected into heparinised or plain tubes for either plasma or serum biochemistry respectively. Coagulation studies and the modified Clauss method of measurement the acute phase protein fibrinogen can only be carried out using sodium citrate containers.
Sample technique: Samples should be collected in an aseptic manner, so as to avoid inducing sepsis, local general, into an otherwise healthy horse. Collection should be sympathetic, otherwise you run the risk of creating the potentially misleading artefacts that result from adrenal induced neutrophilia and splenic contraction.
Timing of sampling: The timing of elective sampling should reflect the questions that are being asked. There is little point in taking post exercise samples or sampling within two or three hours of exercise, if the issue is whether muscle enzymes are within the normal resting range. Samples for elective testing are best collected pre-exercise, early in the morning or alternatively, late in the afternoon when exercise has been completed in the morning.
Sample handling: Misleading artefacts can also arise from poor sampling handling in the period between collection and evaluation in the laboratory. The use of an insulated lightproof container, a laboratory blood sample rack and in hot climates, an ordinary household cold pack, can yield rich dividends in terms of the accuracy and value of the information generated from the sampling. Labelling should be legible and thought should be given to timing of transfer for analysis.
The below clinical pathology reference tables are a general guide. Each horse is an individual and will have its own norms.These reference tables are based on Thoroughbred foals and two or three year old horses in training. All were in good health
and condition on clinical examination. Click on each test to learn more or go directly to the biochemistry blood page.