Blood transfusions

Recently, I was confronted with this IMHA patient, and I realized it had been several months since I'd done a red blood cell transfusion. When running over the physiology in my mind, it became apparent that I was forgetting my book learning, so a refresher was needed. This post will share what I refreshed myself on.

So, just like in humans, we do blood transfusions for anemic animals. We also do transfusion of plasma, as well as immunoglobulin, and platelet rich cryoprecipitate (although this is very rare in the area where I practice). Each type of transfusion has its own nuances.

Dogs, just like all other animals, have blood types. The categories are a bit more confusing than people and include designations such as DEA 1.1, DEA 3, 4, 5, and 7, and DEA positive or negative. For the sake of brevity, I will not go into the differences here. Suffice to say that the most important blood group in dogs is the DEA 1.1 group, as it the most likely to cause severe reactions.

In dogs, it is generally considered acceptable to transfuse a patient once with red blood cells without blood typing them. Why is this the case? Dog red blood cells are identified by the designation DEA. This stands for dog erythrocyte antigen. A dog can be either DEA positive (meaning the dog has little immune system stimulating compounds on the surface of his red blood cells) or DEA negative (meaning there are no compounds on the surface of his red blood cells).

Antibodies are one of the killers that our bodies produce. Antibodies can be directed against viruses, bacteria, and even things like donor blood. Dogs are not born with any antibodies against different blood types. As a result, you can transfuse a dog without blood typing it once. Since there are no antibodies, there will be no immune reaction to the blood. BUT - once you have transfused that patient, you must blood type the patient before transfusing again.

Why? Well, let's say you have a DEA negative dog. There are no compounds on the surface of his blood cells, and his immune system recognizes these red blood cells as "self." You transfuse him with blood from a DEA positive dog that DOES have little compounds all over the red blood cells. The dog has no natural antibodies, so there is no reaction. The body does however recognize that this is not "self" blood, and the immune system makes antibodies to that type of blood. Next time you transfuse, the body will release those antibodies against that unfamiliar, non-self blood, and a severe "allergic" reaction will ensue. It takes 5-9 days for the immune system to produce those antibodies.

There is another interesting way to assess how a dog will react to blood. After blood typing, you can take a combination of the dog's own blood and blood from the donor and mix them together to see if a reaction occurs. If it does, then the blood is not safe for the dog. This is called cross matching and has nothing really to do with blood type. It is merely a way to see if a dog will react to a certain donor's blood. It is very useful in dog transfusions.

The perfect donor dog is DEA 1, 3, 5, and 7 negative, as these are the most likely to cause reactions. It is very interesting to me that greyhounds have a higher prevalence of ideal donors than other breeds of dog. While they make great donors, a high percentage of them (approx 50%) also carry a red blood cell parasite called babesiosis that can cause severe illness and hemolytic anemia. Thus, very careful screening of all blood donors is done before they are accepted as donors.

Cats are a whole different species. Cats have blood type A, B, or AB - similar to humans. Type A is far and away the most common (99% of cats), while Type B is very rare and is often found in purebreeds such as Russian Blues and Devon or Cornish Rex breeds. Cats ARE born with natural antibodies against other blood types. Thus, an A cat will have B antibodies, and a B cat will have A antibodies. Further, in the B cats, these antibodies are so strong that transfusing it with A blood will lead to almost immediate death from a severe anaphylactic reaction. Giving a type A cat B blood will also lead to a reaction, but it is not always fatal. As a result, cats must always, always, always WITHOUT exception, be blood typed. There are type AB cats, but these are <0.4%. They have no natural antibodies and can be universal recipients. I have never seen an AB cat (or a B cat), nor do I expect to.

A B cat given A blood will - within seconds - become restless, may stop breathing briefly, the heart will slow down and the rhythm become irregular, the cat will often vomit, and then collapse. Death is imminent. A milder reaction will happen if a type A cat is given B blood, but it can still be life-threatening.

As a sidenote, kittens developing in utero can have a different blood type than the mother cat. If this is the case, when they are born, the kittens will start nursing. Through the colostrum, they will receive the antibodies that the mother cat has against their own blood type. They rapidly deteriorate due to hemolysis of their own red blood cells. This condition is called neonatal isoerythrolysis and thankfully is rare!

Luckily for us and our patients, we have in-house tests that are (relatively) simple and quick to run that can identify both blood type and whether a reaction will occur to the donor blood (cross match kits). These are imperative for ensuring that our patients are receiving the right blood and make our jobs as veterinarians so much easier.