| Sample quality is of enormous importance in the successful
application of biochemistry and haematology. Good venipuncture technique
is therefore essential. The widespread practice of venipuncture from peripheral
veins, such as the cephalic and saphenous, is often detrimental since flow
from these veins into the needle can be slow and lead to sample artefacts
such as haemolysis and microclots. Sampling from the jugular vein is the
preferred method since this usually produces rapid, unobstructed flow of
blood into the syringe or vacutainer. The technique is simple and can be
used with ease in all but the most obstreperous pets. |
| JUGULAR SAMPLING
FROM CATS |
| * |
Use 21 or 20 g x 1/2-1 inch needles with 5 - 10 ml syringe
attached. Clip the hair over one jugular groove and aseptically prepare
the skin over the jugular vein. |
| * |
Position the cat towards the edge of the surgery table. Hold
the front legs down over the edge with your left hand, and with your right
hand tip the neck backwards and the nose upwards. The front legs and neck
up to the point of the mandible should then be in a vertical plane. The
blood sampler takes up a position in front of the cat and holds off one
jugular vein by compressing the jugular groove. The needle is then inserted
into the vein with the tip pointing upwards. As soon as the tip of the needle
enters the lumen of the vein gentle suction should be applied. |
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| JUGULAR SAMPLING FROM DOGS |
| * |
Use 18 -21 g x 1 inch needles with 5 - 20 ml syringe attached.
Prepare as for the cat. |
| * |
Most dogs will sit for this procedure. Large dogs should be
placed with their back to a wall or table. The holder usually stands astride
the dog with legs behind the dog's shoulders. The person taking the blood
sample squats in front of the dog. The dog's head is tipped back exposing
the jugular grooves and the sampler compresses the jugular vein just dorsal
to the thoracic inlet. In many cases the vein is located by feel more than
sight. The vein is raised and lowered and the jugular groove palpated with
the fingers of the opposite hand to locate the vein. The needle is inserted
with the tip upwards and blood is withdrawn by gentle suction. Small dogs
will usually sit near the edge of the surgery table so that a procedure
similar to that described above for cats can be adopted. |
| HANDLING OF BLOOD SAMPLES |
| * |
Once a sufficient quantity of blood has entered the syringe,
the needle is withdrawn and pressure placed on the vein to avoid haematoma
formation. Blood is transferred into anticoagulant tubes after detaching
the needle from the syringe. The blood is mixed with anticoagulant by gently
rolling the tubes between the palms of the hands. |
| * |
A frequent and unnecessary cause of sample haemolysis is withdrawing
a sample into a syringe and then pushing the needle directly through an
evacuated tube top. The fluid flow under pressure through the needle will
inevitably damage the red blood cells. If blood is to be transferred into
evacuated tubes from a syringe the bung should be removed to release the
vacuum, the needle removed from the syringe and the blood gently expelled
from the syringe. |
| * |
The tubes which are most frequently haemolysed on arrival
at the laboratory are those that contain oxalate fluoride. We suspect that
this is because the oxalate fluoride tube tends to be remembered at the
last minute and frequently is filled with the last remnant of blood in the
syringe which is expelled from the syringe under pressure. Oxalate fluoride
is also quite a potent red cell metabolic toxin and this tube should probably
be filled first with the freshest and least damaged red blood cells. |
| * |
Biochemical artefacts are a problem with postal samples sent
to commercial laboratories. These can be minimised by separating serum or
plasma from clotted or heparinised samples before sending the sample; this
requires a centrifuge. We are experienced at identifying sample artefacts
and in most cases a potential artefact which might affect the interpretation
of blood values will be identified on the laboratory report. |
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