Blood is a part of the circulatory system which comprises of the blood, blood vessels, and the heart. The blood is the red liquid which circulates around the body via the arteries, veins, and capillaries (collectively known as the blood vessels). 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.Just as with people, some times a blood transfusion is necessary to save a cat's life. This may be whole blood (containing all four components of the blood) or blood components (plasma, platelets etc).
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 to be oxygenated. Red blood cells get their colour from hemoglobin (Hb), which is an iron-containing compound. Red blood cells can be stored for up to three weeks.
- 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. Nutrients, antibodies, waste products, blood clotting factors, hormones are also transported in blood plasma. Plasma transfusions are usually performed in cats who have blood clotting disorders.
- Platelets (thrombocytes) - Small, disc shaped cells whose function is to bind together and form clumps in order to plug damaged blood cells.
Why do cats need blood transfusions?
There are a number of reasons why a blood transfusion may be needed including;
- 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.
Are there different blood types in cats?
Yes, cats have three blood groups which are genetically determined. Type A is the most common group, Type B is less common, but is found in some breeds of purebred cat and AB is extremely rare. Blood groups are determined by the type of antigens (markers) which are located on the surface of red blood cells. 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, this test usually only takes a few minutes to perform and requires only 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 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 staff of the veterinary practice will use their own cats to give blood.
More and more veterinary surgeries keeping a list of cat owners 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.
Blood donor requirements:
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.
Prior to donation bloodwork (complete blood count, biochemistry) should be checked. Donor cats should have a calm disposition.
What about blood transfusions from dogs?
I have heard of two cases where in absolute desperation, a cat has received blood from a dog. This 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 a last resort, ideally a cat should receive a feline blood donation.
How is the blood transfusion given?
As the donor cat will need to be sedated, if possible, he should be fasted for 4-6 hours prior to having his blood taken to reduce the risk of vomiting. His blood pressure should be taken prior to donation. 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 catjust before or at the time of collection. Approximately 50ml of blood will be taken (around 1% of bodyweight). It will take around 30 minutes to collect blood from the donor cat. He will be sedated during this process. 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. Heart rate, blood pressure, capillary refill time, respiration rate as well as signs of urticaria and vomiting are all closely watched. If the recipient shows no adverse reactions, then the amount of blood given is increased to 10mk/k/per hour. He will still need to be monitored. It takes around four hours in total.
It is possible for a reaction to occur either during the procedure or several hours afterwards. So your cat will be closely watched.
There are possible side effects to both the donor and the recipient which are outlined below. 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. Generally, this is caused by 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 occurring >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.|
|Allergic (urticaria)||IgE antibodies reacting to plasma protein resulting in mast cells releasing histamine.||Rash (urticaria), redness, itching.|
|Allergic (anaphylactic)||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.|
|Febrile||Antibody reaction to donor white blood cells or platelets.||The most common symptom of febrile reaction is increased body temperature.|
|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.|
|Pulmonary edema||If too much blood is given, fluid can build up in the lungs.||Dyspnea (difficulty breathing), open mouthed breathing, rapid breathing, crackling sound in the lungs, blue-tinged gums.|
|Transfusion-related sepsis||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. Supportive care including oxygen therapy, steroids and antihistamines may be administered.