Understanding Veterinary Blood Transfusions

When thinking about fluid therapy in our patients, we have to consider the correct choice of fluid, for the condition that we are treating.

More often than not, this will be the choice of a crystalloid fluid such as Hartmanns or Saline, which will support the patient’s circulatory system and treat the patient whilst their health is compromised in some way. There are some circumstances where, although a crystalloid or colloid is better than nothing, the only real choice of fluid is whole blood or plasma.

Blood transfusions are becoming more and more common within the veterinary practice. Not only are staff becoming more skilled and experienced at performing a blood transfusion, but they also often have a list of potential donors they can call upon when needed. With several organisations available worldwide to supply practices with canine blood units, whole blood and plasma have never been so easy to obtain. The service is unavailable for feline blood units as the storage requirements differ from that of human and canine blood, and currently, these requirements cannot be met.

Furthermore, whilst minimal specialized equipment is still required to administer whole blood and plasma, transfusion IV set equipment and a certified blood transfusion pump such as Anifusion® are now much more readily available as well.

Why whole Blood?

A blood transfusion is needed to replace a lack of viable blood in the circulatory system. This could be following any kind of trauma that has caused the patient to haemorrhage, or surgery that has resulted in a high blood loss e.g., a splenectomy. Some disease processes result in a lack of blood cells or immature cells to be produced. In all of these circumstances, the patient will have hypovolaemia and the function of the circulatory system will be compromised, leaving the body unable to support a healthy or speedy recovery or even life, and requiring a blood transfusion.

Confirmation for the need for a blood transfusion is based upon clinical symptoms, observation, carrying out an HCT / PCV blood test and calculating loss of blood, by weighing swabs during surgery.

Calculating how much blood may be needed.

As a very general guide, 2ml per kg of body weight is needed to increase a patient’s PCV / HCT by 1%. So, it is important that when using a donor, you choose a suitably sized patient to cover the needs of the recipient. A maximum of 16mls per kg can be taken from Canine donors and a maximum of 10mls per kg, (with a total maximum of 50mls), can be taken from Feline donors. To calculate this more accurately the following formulas can be used:

Dogs: 80 x B/W in Kg x desired PCV increase / PCV of donor blood

Cats: 60 x B/W in Kg x desired PCV increase / PCV of donor blood.

Who can be a donor?

There are many other considerations when choosing a donor and these are listed below.

  • Dogs need to be above 25kg in body weight and cats need to be above 4kg in body weight.
  • Both dogs and cats need to be between 1 to 8 years of age.
  • Both dogs and cats need to be vaccinated but more than 2 weeks ago.
  • Worming needs to be current but more than 2 weeks ago.
  • Ideally, cats should be indoors only if possible.
  • General health needs to be good with a biochemistry and haematology blood screen is performed.
  • No more than 3 to 4 donations per year per donor dog.
  • No more than 4 to 5 times per year per donor Cat.
  • Sedation in dogs is best avoided, so a good temperament is needed.
  • Sedation in cats is recommended with a suitable protocol.

Once your selected Donor has met the criteria listed above, a blood sample should be taken from both the donor and patient to carry out blood typing and cross-matching, to confirm suitability.

Image of dog receiving a blood transfusion, whole donated blood is being given to the recipient patient via a blood transfusion giving set and an IV cannula.

Blood typing

Blood typing is extremely important, as it determines the presence or absence of species-specific inherited antigens, which can be found on the surface of the Red Blood Cells or RBC’s. If the antigen is present, the blood group is determined as Positive and if the Antigen is absent, then the blood group is determined as Negative. 98 % of the population are Negative.

Both dogs and cats can carry naturally occurring antibodies to these antigens. Therefore, if a recipient is given mismatched blood, these antibodies can target the antigens on the RBC’s and cause a haemolytic reaction with devasting consequences.

Dogs have very low levels of naturally occurring antibodies. In most cases, this would mean, that if a dog were to receive a mismatched donation of blood, the likelihood is that it will only result in sensitisation of the immune system to the antigen, and the development of antibodies will occur over 4-5 days.

However, should the patient receive a subsequent mismatched blood transfusion, the antibodies that have now been produced, will target any antigen that is present and haemolytic reactions will occur.

Cats have high levels of naturally occurring antibodies: therefore, blood typing should always be done.

There are commercially available blood typing kits, to determine which blood group your cat or dog belongs to.

Blood types in dogs

Canine blood typing kits are testing for the presence of DEA 1 antigen. It will determine if the patient is DEA 1 negative or positive.

  • DEA 1 negative dogs are viewed as being universal donors as they can be used successfully as donors for both DEA 1 Negative and Positive dogs.
  • DEA 1 Positive dogs can only be used with another Positive dog.

Blood typing in cats

Blood typing for cats uses the AB system.

Testing kits will determine if they are A, B, or AB

  • Patients can only be matched with a donor cat with the same blood type.
  • If no other donor is available, an A cat can be used in an emergency for an AB cat, but this is not typically recommended.


Cross-matching is performed to determine the suitability of blood between donor and patient, and this should be done, even if the blood typing has proved compatible. Commercially available test kits are available which will test to see if the blood samples will be matched or if there is an adverse reaction. Cross-matching can also be done by the provider of commercially available blood units, to ensure the correct blood is dispatched.

Cross-matching should always be done but most especially in the following circumstances:

  • If the patient has already received a blood transfusion (Even if by the same donor)
  • Has had a previous transfusion reaction.
  • Has an unknown previous history.
  • Has been pregnant in the past.

Preparation of both patient and donor

Once the suitability and the compatibility of blood between patient and donor have been established, both animals should be prepared within the clinic setting to either donate or receive the blood. Prior to commencement, general checks such as TPR and HCT / PCV should be taken and recorded, and the donor and recipient allowed to urinate and defecate.

Place a new sterile dedicated IV cannula such as Anicath™ for blood collection and transfusion (with the jugular being the site of choice for collection). The IV cannula for both collection and transfusion should be of the largest gauge possible, to prevent rupture of the RBC’s during the process. If cannula/catheter flushing is required, use saline only: do not flush with any other crystalloid other than saline or sterile H2O. A second IV cannula/catheter should always be placed in both donor and patient to be able to give supportive treatment such as IV fluids and other medications if required.

Donating blood.

Using a commercially available collection bag containing anticoagulants, collect the required volume of blood, gently moving the bag to ensure even distribution of the anticoagulant. Have the collection bag lower than the patient to allow for gravity-assisted collection. It is also a good idea to have a set of small scales handy, to weigh the blood bag as it is collecting, to ensure an accurate amount is collected without excess. 1g in weight = 1 ml in blood.

Once completed, remove the IV cannula/catheter, applying slight pressure to the entry site to stop the bleeding, placing a light dressing if required. The patient should be allowed to urinate and defaecate again and encouraged to eat and drink as soon as possible or as soon as sedation allows. If placed on IV fluids, the donor should remain in the clinic setting until blood loss has been replaced with fluids. Dogs should receive a controlled amount of gentle exercise for the following 72 hours and cats should be kept indoors for 24 to 48 hours. It should be marked on the patient’s records that they have been a blood donor and this exercise should not be performed more than 4 times per year. The Anifusion® cloud reporting system can log the event in the pdf patient infusion report for future reference.

Preparing the blood for transfusion

Collected blood should be used as soon as possible to maintain the heat and used within 4 to 6 hours of collection. If you are using blood (or plasma) obtained from a company such as the Pet blood bank (UK), this should be warmed to room temperature. Do not microwave the blood as this may damage the cells and do not overheat as this may affect clotting and haemolysis and can also encourage any bacterial activity. If using a water bath, place the blood bag in another zip-lock plastic bag to protect the ports from contamination. Connect and prepare a commercially available transfusion line, in much the same way as you would prepare and prime an IV line for fluid transfer, ensuring that the entire line is primed with blood and has replaced all air and dead space before connecting to your patient. Special blood transfusion IV lines are to be used, as they contain an in-line filter with a minimum 25-micron mesh to prevent any blood clots or artefacts from entering your patient whilst allowing the higher viscosity blood to flow.

The Blood transfusion.

The recipient patient must be monitored closely during a blood transfusion. The likelihood of a reaction to the donor blood is greatly minimised if the patient has been correctly blood typed and cross-matched. However, an adverse reaction can still occur, especially if the RBC’s have ruptured at any point during the whole process, causing haemolysis. Reactions are typical of any patient suffering from circulatory distress, such as tachycardia, dyspnoea, tachypnoea, abnormal heart or pulse rhythm, pyrexia, ataxia, hypersalivation, vocalisation, vomiting, muscle tremors or convulsions.

It is for this reason that the donor blood should be infused at a low rate initially, which can be increased and adjusted as the transfusion progresses. A blood certified IV infusion pump, such as Anifusion®, would help in this instance, as extremely low rates can be programmed to be infused accurately and over a pre-set period. We recommend initiating the blood transfusion at 0.25ml per kg per hour, for 15 minutes to check for tolerance. Increase the rate to 1ml per kg per hour. After 15 minutes, the rate can be further increased to 2ml per kg per hour, for 15 minutes. If all is well, then then the blood transfusion rate can be increased to 5 to 10mls per kg per hour, for the remaining duration. A transfusion should not exceed 4 hours in total and an infusion rate no higher than 400ml/hr should be used. A TPR and PCV / HCT should be taken and recorded every 10 minutes throughout.

A dated record should be added that the patient has received a blood transfusion with details pertaining to the amount of blood infused as well as who the donor was. All details of blood typing and cross-matching should also be recorded and filed.

Infusion pumps

Traditionally the use of infusion pumps in blood transfusions has been avoided, because the mechanism of an infusion pump, by its very nature, squeezes and manipulates the IV line in order to produce a drop of fluid. The squeezing of the line could, therefore, potentially cause the rupture of the RBC within the line, causing haemolysis, which in turn causes transfusion reactions and poor patient outcomes.

The Anifusion® IV pump has certificated blood transfusion compatibility, to allow the transfusion of whole blood at rates below 400ml per hour. Anifusion® IV pump can not only be used to deliver whole blood to a recipient patient safely but Anifusion® can also be programmed to do so at the very low rates recommended to deliver the blood, over short periods.

The ml/ hr mode can be programmed to deliver the blood in this way or alternatively the sequence mode can be utilised to deliver the rates that have been pre-calculated for your patient. Whichever mode is chosen, we recommend a member of the clinical team should always be present to be alerted to any sign of circulatory distress or reaction.

HCT = Haematocrit: Blood test performed by a machine to determine the number of Red blood cells in the circulating blood. Expressed as a percentage. EG 40% would indicate that in 100mls of blood 40mls is made up of Red blood cells.

PCV= Packed cell volume: the same as HCT except the blood test is performed manually rather than by a machine.

RBC = Red Blood Cell

B/W = Body Weight

Kg = Kilogram

TPR = Temperature, Pulse, Respiration

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