15 Mar 2025
Deborah James
Job Title
Image: Maxim / Adobe Stock
Blood transfusions are becoming more common in first opinion practice after their introduction in the 1990s (Newfield, 2018) because of their lifesaving properties, but they come with their own risks of transfusion reactions.
This article will look at blood transfusion procedures – why and when we do them, how we conduct them, how we blood type and choose a blood donor, and, finally, the risks of transfusion reactions.
The key point to remember is that we only want to replace the blood product or component that the patient has lost. The reason for this is we can tailor our transfusions to be able to treat individual patients for their specific requirements, leading to a reduction in how much is administered during the transfusion and, ultimately, reducing the risk of any transfusion reaction occurring.
So, what are the different types of products available to us?
Whole blood contains all the blood components: red blood cells (RBC), white blood cells, platelets, plasma proteins and clotting factors. Fresh whole blood must be transfused within 24 hours of collection, and stored whole blood can be stored in a fridge for up to 28 days from the time of collection.
Fresh whole blood is the best source if we want platelets or clotting factors; however, it is important to note that after six to eight hours, the platelet levels decrease and are totally lost at 72 hours (Godinho-Cunha et al, 2011). These are suitable for our haemorrhage patients.
Packed RBCs contain RBCs, white blood cells, non-viable platelets and remnant plasma; they have a packed cell volume (PCV) of approximately 60% to 70%; and a shelf life of 35 to 42 days – however, a recent study conducted by Ferreira et al (2018) has shown this is potentially shorter due to haemolysis after around 28 to 31 days. These are suitable for our anaemic patients.
Fresh frozen plasma is plasma that has been separated from the whole blood product and has been stored at -18°C within six to eight hours of collection, and contains plasma proteins and clotting factors, with a shelf life of a year (Lane and Sinnott-Stutzman, 2020).
If it has not been used within this year, then it becomes frozen or stored plasma and has a shelf life of an additional four years. This product is suitable for those with coagulopathies such as von Willebrand disease.
Frozen plasma or stored plasma is plasma that has gone past its one-year shelf life, as described; has been stored incorrectly; or plasma that was not separated in the initial six to eight-hour window. It contains immunoglobulins and plasma proteins, as well as most clotting factors, but is not suitable for von Willebrand patients. Instead, this product is versatile and can be used for the majority of bleeding disorders (Lawrence-Mills et al, 2024).
Cryoprecipitate contains high levels of clotting factors and can be used in our von Willebrand patients (Jones, 2022).
Platelet concentrate can be frozen or fresh, but it does require constant agitation and has a shelf life of one week (seven days). It can be used in thrombocytopenia patients and contains platelets and plasma, as well as non-viable leukocytes (Jones, 2022).
Human serum albumin is a one-time only treatment option for our patients and is only indicated in critically ill patients with hypoalbuminaemia. We do not use plasma in these patients, as we would need six times the volume of human serum albumin due to being a poor source of albumin (Horowitz et al, 2015).
So, how do we decide who should receive a blood transfusion? The classic definition of a “transfusion trigger” is the PCV or haemoglobin level indicates it, but as with most things, it’s not quite this straightforward (Poli, 2024).
Some key questions should be asked and aspects assessed to come to a well-rounded solution, such as:
The normal blood volume is approximately 85ml/kg to 90ml/kg for dogs and 60ml/kg to 65ml/kg for cats, and we ideally want to administer the transfusion over four hours due to the risk of bacterial contamination once the product has been broached (Jones, 2022). In patients with cardiac disease, it can be given up to six hours.
Asepsis and careful handling is vital. Defrosting or warming your product should be done to a maximum temperature of 37°C; it is safer to transfuse cold blood than excessively warm blood, so allow the blood to reach room temperature (Jones, 2022). Sterile gloves should be worn when handling the product, preparing the product and attaching it to the giving set or syringes.
Ensure that no calcium-containing medications or fluids (for example, Hartmann’s) is given in the same line as the blood, as it can cause calcium lumps to form (Jones, 2022).
It is also recommended not to feed the patient during the transfusion to enable the administrator to assess what a reaction is.
Blood should be administered at 0.25ml/kg/hr to 0.5ml/kg/hr for the first 30 minutes, then, if no reaction is observed, it can be increased to 1ml/kg/hr for a further 30 minutes; providing no reaction occurs, the rate can be increased to deliver the entire transfusion over four to six hours (Jones, 2022).
Firstly, what is blood typing? Blood groups are defined by which antigens are on the surface of the RBCs; we want to identify these, as this is where our haemolytic transfusion reactions will occur if an antibody is working against a blood group antigen (Oliveira, 2012).
Dogs have 12 RBC antigens that we know of, which are known as dog erythrocyte antigens (DEAs). These can present themselves in various different combinations; testing for them is not practical, so we test for DEA 1, which is likely to cause the most severe transfusion reaction (Jones, 2022).
Dogs will develop antibodies approximately one to two weeks after their primary transfusion, meaning that any future transfusions using the same type blood will elicit an acute haemolytic reaction, destroying all transfused RBCs within 12 hours of administration (Oliveira, 2012).
Cats, meanwhile, have only four known RBC antigens. A is the most common and, in Siamese cats, 100% of the population is type A (Taylor et al, 2021); B is less common, but can be found in higher prevalence in pedigree breeds such as the British shorthair, Birman and Devon rex (Taylor et al, 2021); type AB is very uncommon.
The fourth type is known as the Mik antigen and has only been recently discovered, so its prevalence in the feline population is unknown and currently cannot be tested for in the UK.
Unlike our canine patients, cats do have naturally occurring antibodies. Type B cats cannot have type A blood – it will result in a fatal transfusion reaction. Type AB cats do not have antibodies against either type, and type A cats have very low levels of antibodies against the type B (Jones, 2022).
We have probably all encountered fading kittens at some point in our careers. After Knottenbelt et al (1999) studied this condition further, they found the root cause to be neonatal isoerythrolysis (NI). Our newborn kittens gain antibodies from the colostrum of the queen during their first few days of life, which can lead to intra-vascular or extra-vascular haemolysis in the kittens with an incompatible blood type to that of the queen (Oliveira, 2012).
This can be avoided by avoiding incompatible mating or, alternatively, not allowing the kitten to feed from its incompatible mother for the first 24 hours, and instead find a type A or AB queen to safely give the colostrum (Oliveira, 2012).
Cross-matching is, essentially where we allow a transfusion reaction to occur outside of the patient’s body to assess compatibility while not compromising patient safety.
Two cross-match tests exist, dependent on which type of blood product or component is being transfused: major cross-match is recommended for RBC products, and minor cross-match is recommended for plasma products (Barnett, 2012). Anticoagulated whole blood contains both of these components and, therefore, it is advised to perform both a major and a minor cross match when transfusing this (Barnett, 2012).
Major cross-matching assesses the compatibility between donor RBCs and the recipient plasma/serum, while minor cross-matching assesses the compatibility between the donor plasma/serum and the recipient RBCs (Barnett, 2012).
Xenotransfusions occur when canine whole blood or packed RBCs are transfused to feline patients, normally because of a greater availability of canine blood and in larger quantities, or the owners have financial constraints (Taylor et al, 2021).
It is mainly used in cats with anaemia as a way to stabilise the patient short term, to allow for further investigations or blood typing to take place (Taylor et al, 2021).
These transfusions can only occur once during the cat’s life – antibodies detect the new RBCs in four to seven days and destroy them (feline RBCs are present for 30 days before being destroyed), and any future xenotransfusions will lead to anaphylaxis and, most likely, a fatal outcome (Taylor et al, 2021).
Autologous transfusion or autotransfusion is the process where the patient’s own blood is used as a transfusion in cases such as a haemothorax and cross-matching, or typing is not required (Taylor et al, 2021).
So, what makes a good donor? In our canine patients, the key points to look for are:
In our feline donors, as detailed by Jones (2022):
It is important to note that while the pet blood bank does exist, it only caters for canine blood. Currently, no UK feline blood bank exists, and so the majority of our feline patients will receive fresh whole blood as a transfusion.
Blood transfusion reactions can be acute or delayed onset, and vary in presentation from minor to life threatening in some cases; the prevalence of these reactions has been recorded to be as high as 38% (Odunayo et al, 2021).
Treatments for these reactions can be challenging. While many evidence-based guidelines exist in human medicine, very little exists in the veterinary world, meaning treating these reactions can pose many problems (Odunayo et al, 2021).
Six differing types of transfusion reactions exist:
Transfusion reactions are more commonly seen in canine patients than in cats; 28% in dogs in comparison to 8.7% in cats (Yagi, 2016).
The most common clinical signs were pyrexia (53% of cases) and vomiting (18% of cases), and while signs such as tachycardia and tachypnoea could be associated with a transfusion reaction, our anaemic patients will likely already be tachycardic as a result of the reduced oxygen carrying capacity, so is not the most reliable parameter (Yagi, 2016).
Seizures, cardiac arrest, arrhythmias and hypotension are all signs of acute haemolytic reactions (Jones, 2022). Vomiting, hives and erythema are seen in non-haemolytic reactions.
It is really important that every practice conducting blood transfusions should have the ability to track donors to recipients, and vice versa (Rooney, 2022).
Transfusion logs should be clear and eligible, and should include the following details, as set out by Rooney (2022):
It is also important to record our donors. Patients can normally donate two months after their last donation, but this is a minimum requirement, so veterinary nurses need to be making the team aware if they believe the donor is not ideal.
Donation record keeping should include the following:
To conclude, veterinary nurses play an important role in blood transfusion from start to finish, and are vital in advocating for both the donor patient and the recipient patient.
Being involved in these cases and being allocated this level of responsibility in practice can be very rewarding both for your own training, as well as seeing a patient improve in front of your eyes.
Most patients will never need a blood transfusion, but for the minority that do, it can prove to be a life-saving measure.
