A blood transfusion is a life-saving procedure where blood or blood products from a donor are given to a cat to treat a medical disorder. This may be whole blood (containing all four components of the blood) or blood components (plasma, platelets etc).
Blood is a part of the circulatory system which comprises of the blood, blood vessels, and the heart. Blood is the red liquid which circulates around the body via the arteries, veins, and capillaries. It carries oxygen and nutrients around the body and removes waste products such as carbon dioxide. The average 5kg cat has about 325ml of blood. Blood has four components; red blood cells, white blood cells, plasma, and platelets.
- Red blood cells (RBC/erythrocytes) – The most abundant cell in the blood, RBC’s are disc-shaped, concave cells which carry oxygen from the lungs to the tissues, and carry carbon dioxide from the tissues back to the lungs for oxygenation. Their red colour comes from hemoglobin (Hb), which is an iron-containing compound.
- White blood cells (leukocytes) – These cells are responsible for fighting infections from bacteria, viruses, and parasites.
- Plasma – Plasma is the pale/straw coloured liquid component of the blood. It is made up of water, proteins, electrolytes, and sugars and its main role is to transport blood cells around the body. Plasma also transports nutrients, antibodies, waste products, blood clotting factors, and hormones. Cats with blood clotting disorders usually receive plasma transfusions.
- Platelets (thrombocytes) – Small, disc-shaped cells whose function is to bind together and form clumps in order to plug damaged blood cells.
A blood transfusion may be necessary for the following reasons:
- Loss of red blood cells due to destruction (immune diseases, poisoning) or blood loss (trauma, internal bleeding, parasites, surgery etc.)
- A decrease in production of red blood cells.
- Low white blood cell count (leukopenia), due to cancer, some infections, autoimmune disorders, kidney or liver failure, certain medications, congenital disorders.
- Blood clotting disorders.
- A is the most common group
- B is less common but is found in some breeds of purebred cat
- AB is extremely rare
The type of antigens (markers) on the surface of blood cells determine the blood group. So, if you have a cat who is blood group A and he receives blood from a type B cat, naturally occurring alloantibodies in the recipient’s blood will cause an immune response due to the type B antigens on the red blood cells of the donated blood. Therefore when receiving blood, the following must occur.
- Type A cats can only receive type A blood.
- Type B cats can only receive type B blood.
- Type AB cats can receive blood from type AB blood or type A blood.
Furthermore, in 2007 a new antigen known as MiK was discovered. Most cats have the MiK antigen on their red blood cells, however a small percentage of cats do not have it, and if they receive a blood transfusion from a cat who does have the MiK antigen a reaction may occur, even if both the donor and the recipient have the same blood type (A, B or AB).
Testing is usually able to be performed in-house, and only takes a few minutes to perform, with a small amount of blood. In addition to testing the blood groups, cross-matching (BCM) may be performed to determine the compatibility of the patient and donor blood. This is even more important if your cat has received a blood transfusion in the past.
Where does the donated blood come from?
The donor cat may be a practice cat who permanently resides at the veterinary surgery (a homeless cat who the practice adopts). Often cats owned by the staff of the veterinary practice will use their own cats to give blood.
More and more veterinary surgeries keeping a list of cat guardians who are willing to have their cat donate blood upon request. This takes the pressure off one or two practice cats and means they always have a standby supply of emergency blood. Pet blood banks are also starting to become more commonplace in the US and the UK.
Obviously, not all cats are suitable blood donors, the donor cat should meet the following criteria:
- Be in good health with no pre-existing conditions.
- Weigh least 4kg.
- Be fully vaccinated.
- Be free of parasites and up to date with parasite treatment.
- Screened for FIV, FeLV and Mycoplasma hemofelis.
- Have a packed cell volume of >35%
- Not be pregnant or lactating.
- Donor cats should have a calm disposition.
There are at least two cases where a cat has received blood from a dog as a last resort, which is known as xeno transfusions. Dogs have eleven blood groups, however, cats don’t have naturally occurring antibodies to canine blood. Xenotransfusions have been used when no other options are available and the cat will die without an immediate transfusion. This is the last resort, ideally, a cat should receive a feline blood donation.
The donor cat should not have eaten 4-6 hours prior to taking blood to reduce the risk of vomiting during sedation and the veterinarian will check the cat’s blood pressure. A needle will be placed into a large vein, usually the jugular (in the neck). Collection of the blood usually takes around 30 minutes. Once the blood donation has finished, the donor cat should be monitored for signs of low blood pressure. Supplementary fluids are often given to the donor cat just before or at the time of collection. Approximately 50ml of blood will be taken (around 1% of body weight). It will take around 30 minutes to collect blood from the donor cat. A cat can only donate blood every 3 months.
Initially, blood is given at a rate of 0.5mk/k/per while being closely monitored to watch for complications. Your veterinarian will monitor the heart rate, blood pressure, capillary refill time, respiration rate and watch for rash and vomiting. If the recipient shows no adverse reactions, then the amount of blood given is increased to 10mk/k/per hour. It takes around four hours in total.
A reaction can occur during the procedure or several hours afterward. Close monitoring is necessary.
Outlined below are possible side effects to both donor and recipient.
There are two types of side effects which may occur in the recipient. Immune-mediated and non-immune-mediated.
Acute hemolytic reaction (AHTR)
This occurs when the recipient has pre-existing antibodies to antigens in the donor cat’s blood due to mismatched blood. Ie; a cat with type A blood receiving a transfusion of type B blood. This results in a destruction of the donor red blood cells in the blood vessels.
Fever, low blood pressure, restlessness, tachycardia (rapid heart rate), difficulty breathing, cyanosis, abnormal bleeding, vomiting, diarrhea, oliguria, hemoglobinuria, hemoglobinemia, shock, and collapse.
Delayed hemolytic reaction (DHTR)
Usually occurs >24 hours after the transfusion has occurred, caused by an immune reaction to minor red blood cell antigens.
There are usually no clinical signs other than a loss of transfusion efficiency.
IgE antibodies reacting to plasma protein resulting in mast cells releasing histamine.
Rash (urticaria), redness, itching.
IgA antibodies reacting to plasma protein resulting in a severe allergic reaction.
Low blood pressure, tachycardia (fast heart rate), bronchospasm (narrowing of the airways), collapse.
Antibody reaction to donor white blood cells or platelets.
Elevated body temperature is the most common symptom.
Transfusion-associated circulatory overload (TACO)
Caused by a rapid transfusion of a large volume of blood, the circulatory system becomes overwhelmed.
Dyspnea (difficulty breathing), heart failure, high blood pressure, swelling.
Fluid can build up in the lungs if the cat receives too much blood.
Dyspnea (difficulty breathing), open-mouthed breathing, rapid breathing, crackling sound in the lungs, blue-tinged gums.
It is possible for a cat to become infected due to an infection in the donor cat’s blood.
Fever, low blood pressure, shock.
While this list may look daunting, please be aware that while side effects can and do occur, they are usually quite rare, especially if blood typing and cross-matching take place prior to your cat receiving a blood transfusion.
What happens if a reaction occurs?
The blood donation will need to stop if the recipient shows an adverse reaction. Administration of oxygen, steroids, and antihistamines may be necessary.