Transfusion Medicine

Blood types

The red blood cell membrane is covered proteins and complex carbohydrates and hence is antigenic. Patients recognise these foreign antigens as non-self when they receive a transfusion and stimulate antibody production.

Blood types in dogs

Canine blood groups are classified by the Dog Erythrocyte Antigen (DEA) system. Currently there are 6 recognised DEAs (1.1, 1.2, 3, 4, 5 and 7) and dogs can be either positive or negative (i.e. A+ or A-) for each group. At present there are easily available tests for DEA 1.1 only. There are no naturally occurring alloantibodies to1.1. or 1.2 and so these blood types will not typically cause an acute reaction to a recipients first transfusion. However if a DEA 1.1 negative dog receives a DEA 1.1 positive transfusion antibodies will be formed and a second transfusion with DEA 1.1 positive blood will cause a haemolytic transfusion reaction. This sensitization typically takes 1-2 weeks to occur as it requires the production of antibodies. Antibodies are also formed to the other blood types. As it is only possible to type dogs for DEA 1.1 cross matching should always be carried out when a recipient has been previously transfused.

Blood types in cats

Three blood types have been described in cats; A, B and AB which is thought to be rare. Cats have preformed antibodies to other blood types and administration of the incorrect type can result in rapid and fatal consequences. All cats MUST be blood typed before a transfusion and should only receive type specific blood.

Anticoagulant-preservative solutions

Generally anticoagulants used for blood collection include either heparin or citrate. The citrate solutions contain agents that act to preserve the red blood cells. Preservative solutions such as Adsol are now widely used. These allow red blood cells to be stored for up to 35 days and protect them against trauma.

Blood collection

Typically dogs do not require anything more than gentle restraint. Blood may be taken under gravity or gentle vacuum, it is useful to be able to weigh the blood during collection so that the quantity taken is known (1ml blood weighs 1.06g). The minimum amount that may be taken into a human collection bag is 300ml and the maximum 495ml. Cats typically require sedation, after placement of a cephalic catheter we use 2-3mg/kg ketamine and 0.25mg/kg midazolam i/v immediately prior to collection. Blood is taken from the jugular vein using a 19G butterfly winged catheter attached to a 20ml syringe prefilled with anticoagulant (CPDA at 1:7-1:9, i.e 3ml of CPDA in every 20ml syringe). It is easier to take blood into 3x20ml syringes.

Blood products

Whole blood can be made into a number of products. These include packed red blood cells, fresh frozen plasma, frozen plasma, cryoprecipitate and platelet rich plasma. [...]