Haematology
Haematology refers to the evaluation of blood cells. Haematological testing is a common and useful diagnostic procedure. A variety of tests may be performed.
A "complete blood count" (CBC) refers to a panel of haematological tests that are commonly used as a health check, before anaesthesia or a "wellness screen".
CBC tests (this list is not exhaustive):
- Red blood cell counts (differential and absolute values) and indices
- White blood cell counts (neutrophils, basophils, eosinophils, lymphocytes, monocytes)
- Haemoglobin concentration
- Packed cell volume (PCV)
- Blood smear evaluation
- Reticulocyte count
- Total protein
- Platelet count
- Bone marrow evaluation (in patients whose CBC displays abnormalities indicative of bone marrow dysfunction)
Reference ranges
These normal values or reference ranges report expected results for normal animals. Note that these values are affected by many factors. The following list is not exhaustive:
- Testing method
- Animal species
- Animal age
- Animal gender
- Animal breed/type
- Reproductive status
- Type of equipment used
Sample reference ranges from the Merck veterinary manual are available here. Note that where possible you should always use the specific range range from the laboratory or manufacturer of the equipment that you are using, as they vary.
Plasma, serum and whole blood
Remember that whole blood consists of cells suspended in a liquid (plasma). Once exposed to air after collection normal whole blood will clot rapidly. If a test is to be performed on whole blood then it must be mixed with an anticoagulant chemical immediately after collection from the animal. This will stop it clotting and enable successful testing. Mix the blood with the anticoagulant by gently rocking the container. Vigorous shaking should be avoided as it can damage the cells and result in haemolysis (red blood cell rupture with the leakage of chemicals from the RBCs into the plasma).
Plasma is the liquid proportion of the blood. If it is required for testing it is obtained by centrifuging an anticoagulated blood sample to separate it from the cells.
Serum refers to plasma minus its fibrinogen, which has been removed during the process of clotting. In this case the blood is collected into a plain tube (no anticoagulant) and allowed to clot. The free fluid that remains around the clot is the serum.
Anticoagulants
A variety of anticoagulants are available and the choice depends on the test to be performed. Always check when collecting samples to ensure you have what you need and don't need to go back and sample the animal for a second time.
Blood tubes are available that contain anticoagulant in the correct proportion to the size of the tube. For this reason always check that the container is filled to the indicated mark on the label. Tubes have an expiry date, check this before use to ensure it is in-date and will therefore work correctly. Once the tube is full, check the lid is secure, label it with the patient details and date/time, rotate it gently to mix throughly and place in the fridge for storage unless being tested within the hour.