Administering a Blood Transfusion

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This determines the serological compatibility of the red blood cells of the blood donor and the recipient.

The major cross match determines the compatibility between the donors red blood cells and the patients plasma. This is analysed by the presence of agglutination.

The minor crossmatch assesses the interaction between the patients red blood cells and the donors plasma. Minor cross match incompatibilities are of concern when large amounts of plasma are being transfused.

Cats should always receive cross matching tests for both the donor and recipient. Even if crossmatching has been undertaken monitoring is paramount as transfusion reactions are still possible.

Crossmatching in dogs should be undertaken if the recipient's transfusion history is unknown or if they have received a transfusion more than 5 days earlier, have been pregnant, or have ever suffered a transfusion reaction before.

Donor Selection

A thorough history and physical exam of the donor should be undertaken prior to each transfusion to ensure they are in good health. Haematology, Biochemistry, infectious disease screening and blood typing should be undertaken before a potential donor gives blood. Ideally donors will have not travelled outside the UK and hence avoided contracting exotic blood borne diseases. Donors should be of a certain weight, dogs at least 25kg and cats at least 4.5kg. Cats should ideally have been tested negative for FeLV, FIV and Mycoplasma haemofelis prior to each donation.

Additionaly it is important to use donors with a good temperament who will tolerate the procedure.


Firstly all equipment required for the transfusion should be prepared and ready, including either a commercially available blood collection bag or a syringe filled with the correct amount of anti-coagulant (commercial bags contain anticoagulant at a ratio of 1ml to 7ml of blood). Heparin is not recommended. The commercially prepared bags contain CPD CPDA1 or ACD which will keep the blood viable for 21-28 days. Dogs can donate standing, sitting or lying in lateral recumbency and the jugular vein should be prepared aseptically.

If using a syringe a catheter is placed into the jugular vein and ideally collection should be performed in one stick to avoid activation of coagulation factors and blood cell damage. Collection bags have a needle attached which can be used to collect the blood.

Dog donors can safely give 11-18mls/kg of blood every 3 weeks.

Cats need to be sedated and laid in sternal recumbency. They can safely donate 10-12mls of their body weight every 3 weeks. Additionally an intravenous catheter should be placed allowing fluid losses to be replaced with crystalloid fluids amounting to 30mls/kg.

Monitoring during a transfusion

Due to the risk of a transfusion reaction occurring any patient receiving a transfusion should be closely monitored. Baseline recordings of the animals temperature, heart rate, mucous membrane colour, capillary refill time, pulse rate and quality, respiratory rate, haematocrit and total protein values should be recorded. They should then also be recorded frequently during the transfusion. If any parameters suddenly change then the transfusion should be stopped.

Adverse Reactions

Haemolytic and non-haemolytic (immunologic) and non immunologic transfusion reactions can occur.

Haemolytic reactions cause intravascular haemolysis and animals present pyrexic, tachycardic, dyspnoic, weak, collapsed, vomiting, and with haemoglobinaemia and haemoglobinuria. This can lead to renal damage and shock. Additionally a delayed haemolytic reaction can occur 2-21 days after the transfusion with similar signs as haemolytic reactions.

Non-haemolytic reactions involve an acute hypersensitivity reaction where patients present with a range of signs from pruritus, erythema, oedema, dyspnoea and urticaria.

If a reaction does occur then the transfusion should be stopped and the patient should be closely monitored. If the reaction subsides the transfusion may be started again at a 1/4 of the original rate. If there is evidence of anaphylactic shock then intravenous fluids, antihistamines, adrenaline and colloids may be given.

Non-immunologic reactions can include an anaphylactic reaction, polycythaemia, hyperproteinaemia, hypothermia, thrombosis, microbial contamination, hyperkalaemia, acidosis, air embolus and transmission of infectious diseases.

See also: Indications for Blood Transfusions
Blood Groups
Blood Groups - Dog
Blood Groups - Cat
Blood Products

Administering a Blood Transfusion Learning Resources
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Test your knowledge using flashcard type questions
Small Animal Emergency and Critical Care Medicine Q&A 12


Transfusion Therapy. Lymphoreticular and Haematology module. 4th year notes. Royal Veterinary College London. 2009.

Selected Topics in Canine and Feline Emergency Medicine. Volume 1. Handbook for the veterinary practitioner. Royal Canin.

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