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,
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 primary 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
- Platelets (thrombocytes) – Small, disc-shaped cells
whose function is to bind together and form clumps to plug damaged
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 the 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 occurs 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.
- A group cats can only receive type A blood.
- B group cats can only receive type B blood.
- AB group 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 the 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 cats to give blood.
More and more veterinary surgeries are keeping a list of cat guardians who are
willing to have their cat donate blood upon request which 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.
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.
- Indoors only.
- 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.
Blood donations from dogs
There are at least two cases where a cat has received blood from a dog as a
last resort, which is known as xenotransfusions. 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 before 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 is monitored for signs of low
blood pressure. Extra 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 about 30 minutes to collect blood from
the donor cat. A cat can only donate blood every three 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
A reaction can occur during the procedure or several hours afterwards. 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
Fever, low blood pressure, restlessness, tachycardia (rapid heart
Delayed hemolytic reaction (DHTR)
Usually occurs >24 hours after the transfusion has occurred, caused
There are usually no clinical signs other than a loss of transfusion
IgE antibodies reacting to plasma protein resulting in mast cells
Rash (urticaria), redness, itching.
IgA antibodies reacting to plasma protein resulting in a severe
Low blood pressure, tachycardia (fast heart rate), bronchospasm
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
Dyspnea (difficulty breathing), heart failure, high blood pressure,
Fluid can build up in the lungs if the cat receives too much blood.
Dyspnea (difficulty breathing), open-mouthed breathing, rapid
It is possible for a cat to become infected due to an infection in
Fever, low blood pressure, shock.
While this list may look daunting, please be aware that while side
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