Detailed guidance on blood withdrawal in laboratory animals is given by Morton et al, 19931. The recommendations relating to good practice and refinement given in this report are still highly relevant.
Before collecting any samples, review your laboratory protocol for labelling, transport and storage of the material. Ensure you have sufficient sample tubes or containers, that they are appropriately labelled, and that you have sufficient appropriately sized syringes and needles if these are required. If you need to freeze your samples, or store them on ice, make sure the equipment and supplies required are readily available. It is often helpful to have an assistant, both to restrain the animal and to make sure the samples are correctly handled.
The volume of blood to be collected must be carefully assessed in relation to the animal’s total blood volume. Volumes in excess of 15% as a single sample may be associated with immediate adverse effects, and >20% is likely to cause hypovolaemic shock. It is generally considered that withdrawal of 10% or less as a single sample causes only minor physiological disturbances. Sampling can usually be repeated every 3-4 weeks. If repeated samples are needed at more frequent intervals, then the volume of blood should be reduced when possible to avoid producing adverse effects.
The stress associated with blood sampling may alter a number of physiological parameters, and this may be avoided by use of indwelling catheters, allowing sampling with minimal restraint. Animals (including rodents) can also be trained to accept blood sampling, using positive reinforcement training methods, resulting in a reduction in stress-related changes in blood constituents.
Whichever site is selected for venepuncture, it should be cleaned and if required, hair removed. This will help maintain asepsis and make locating the vein and accurate needle or catheter placement easier.
As with any other procedure, it is always advisable to check the relevant Project licence plan of work and protocol, your Personal licence and training records, and the specific study protocol. Check the cage or pen label of the animals to be sampled, and the identity of each individual animal if multiple animals in a cage are to undergo the procedure.
After completing the procedure, record that it has been undertaken on the cage label and in your laboratory notebook. If blood has been collected, ensure that effective haemostasis has been achieved before returning the animal to its cage.