Blood Collection
Blood collection is an important part of everyday veterinary practice. Many factors are taken into consideration when deciding where to withdraw the sample. This includes:
- Type of animal
- Size of animal
- Medical condition/site of injury
- Amount of blood to be collected
- Tests to be performed
- Experience of person taking sample
When taking a blood sample, the procedure should be performed in an aseptic manner. This includes:
- Clipping of site
- Preparation of site with surgical scrub solutions
- Washing hands
- Sterile needle and syringe
The sample should always be a ‘clean stick,’ otherwise haemolysis of the sample will occur, which may affect test results.
The aim when collecting blood is:
- To use a vein close to the surface of the body
- To be able to gently withdraw a suitable volume of blood (to minimise damage to blood cells)
- To cause minimal disturbance and discomfort to the animal
Preferred Sites for Blood Collection
In small animal practice the jugular vein is often the preferred site for collection. However, if performing tests requiring only a small amount of blood (e.g., glucose, PCV/TPP), peripheral veins may be used.
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Canine
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Vena jugularis, vena saphena and vena cephalica for central venous blood. Edge of ear (close to base) for peripheral blood smears
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Feline
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Same as dog but avoid saphenous and cephalic veins if at all possible
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Pocket pets
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Tail vein (e.g., rats, ferrets, guinea pigs, etc.)
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Avian
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Jugular vein, brachial artery (for large parrots), pedal artery (large water fowl)
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Equine
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Jugular vein
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Bovine
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Jugular vein, tail vein
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Collection site
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Suggested needle size*
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Cat and small dog cephalic or saphenous vein
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23–25G
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Cat and small dog jugular vein
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21–23G
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Medium to larger dog cephalic or saphenous vein
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21–23G
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Medium to larger dog jugular vein
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20–21G
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Horse jugular
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18G
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When transferring blood from the syringe to the tube, steps are taken to minimise damage to the cells:
- Remove needle from syringe so that blood is not transferred through a small bore.
- Remove top from tube. This applies equally to a vacuum collection tube as to a screw-top tube unless specifically stated by the manufacture. Plunging a blood-filled syringe + needle into a vacuum tube and allowing it to transfer into the vacuum tube increases the possibility of haemolysis.
- Gently expel the blood into the angled tube so it dribble down the side.
- Replace lid securely and (in an anticoagulant tube) gently agitate to evenly mix chemicals with blood. Do this by slowly inverting the tube every 2–3 seconds for 30 seconds.
Factors during the collection that can influence sample quality
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Factor
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How it may affect the sample
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Fear and stress of the animal
Experience and capability of person collecting the sample
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Adrenalin release affecting glucose and some white cell count results.
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Preparation of the collection site
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Contamination of sample will give false results where sample is to be cultured.
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Time of day when sample is collected
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Some hormone levels vary throughout the day.
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Feeding before sample collection
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Will give a transient hyperglycaemia and hyperlipidaemia.
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Using the correct tube for the required test
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Tubes are used for specific tests (e.g., blood in a potassium EDTA tube will give a false potassium level).
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Actual site of collection
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Arterial gasses cannot be estimated from a venous sample.
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Why it is important to conduct preanaesthetic blood tests?
A full patient examination performed by the Veterinarian may not be enough to detect an underlying issue and unfortunately illnesses or diseases can go unnoticed. Preanaesthetic blood tests can check the kidney and liver function, presence of low red blood cell (anaemia), infection or inflammatory disease (high white blood cell count), dehydration (high red blood cell count and high total protein levels).
It is important to know the names and what increased and decreased values could mean to a patient in your nursing care.
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Test
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High
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Low
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Alkaline phosphatase (ALPKP)
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Liver disease such as Cushing’s, active bone growth (seen in young pets)
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Creatinine (CREA)
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Kidney disease
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Overhydration
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Blood glucose (GLU)
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Diabetes, stress (seen in cats)
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Liver disease, infection or certain tumours.
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Aminotransferase (ALT)
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Liver cell injury/damage
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Total protein (TP)
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Dehydration, inflammatory condition
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Decreased liver function, blood loss, gastrointestinal loss and kidney loss
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Blood urea nitrogen (BUN)
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Kidney disease or dehydration
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Liver disease
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Packed cell volume (PCV)
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Dehydration, marrow cancer
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Anaemia
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References
1. The Animal Industries Resource Centre Course materials – Certificate IV in Veterinary Nursing.