What are the Indications for Blood Transfusions?
Blood transfusions are indicated for the management of anaemia, coagulation problems, and rarely for platelet problems and low protein levels. The decision to conduct blood transfusion is based on the dog's history, presenting signs, laboratory test results and underlying cause of the problem. There is no specific transfusion trigger point indicating when to conduct blood transfusion with respect to the dog's falling blood volume or increasing clotting time (i.e. time for blood to clot), although in many cases the aim is to keep the Pack Cell Volume above 20%.
Blood transfusions can be given as a fresh whole blood sample, or a full blood sample that has been refrigerated up to five weeks, or can be given as a component of blood (i.e. only the red blood cell component or only the plasma component). Each of these has different purposes, for example fresh blood will replace the red blood cells, clotting factors and platelets, whilst stored plasma will only replace clotting factors and proteins.
What is Blood Typing?
Both the blood donor and recipient must be blood typed so as to ensure efficient and safe blood transfusions. A cross match should also be performed if the recipient has received a blood transfusion previously.
Blood types are genetic markers on the surface of red blood cells. Dogs that have never received a blood transfusion do not have antibodies that will cause a reaction to a first transfusion. Sensitisation to the particular blood type will occur when a dog has previously received blood from a potentially incompatible donor. Therefore, a severe reaction may occur in the subsequent blood transfusion if this dog is again transfused with the same 'donor blood type'. Such sensitisation can be prevented if blood typing is conducted prior to the initial transfusion so that only compatible blood types are given to the recipient.
What is Blood Cross Matching?
A blood cross match detects the compatibility between an anaemic recipient and potential donor, and is tested in any dog that has received a previous transfusion. It is conducted with anticoagulated blood from both the recipient and potential donor and checks for the presence or absence of antibodies in their blood without determining the blood type.
How are Transfusions Administered?
Standardly blood transfusions are administering intravenously with the rate of transfusion being governed by the recipient's cardiovascular system status, and degree of dehydration and anaemia. Blood transfusion is slow initially so as to observe any transfusion reaction. It is then increased so that the transfusion can be completed over about four hours. The response to the transfusion is monitored by checking the Pack Cell Volume reading and protein level of the blood before, during and 24 hours after the transfusion.
What Reactions Might Occur in Blood Transfusions?
Although blood transfusions are normally a safe and effective form of therapy, there are some risks involved and adverse reactions may occur during or shortly after the transfusions. Most of the reactions can be avoided by selecting healthy donors and performing blood typing and cross matching before transfusions.
The most common signs of blood transfusion reactions are fever, vomiting and haemolysis (breaking down of red blood cells). Haemolytic reactions can be fatal whereas fever and vomiting are usually self-limiting. Most reactions can be overcome by reducing the transfusion and administering anti-histamines and cortisols.