Blood Types, Blood Transfusions, and Blood Donation

Blood types are classified based on specific surface structures on red blood cells, known as antigens.

Cats

Cats, like humans, have blood types A, B, or C (=AB). The distribution of blood types depends heavily on the breed. European Shorthair cats usually have blood type A, while other breeds, such as British Shorthairs, more commonly have blood type B. Cats are born with antibodies against blood group antigens other than their own. Therefore, the blood group must be carefully considered starting with the very first blood transfusion. Otherwise, severe incompatibility reactions can occur.

Dogs

There are a total of twelve blood groups in dogs. However, testing is limited to the DEA (Dog Erythrocyte Antigen) 1.1 positive and DEA 1.1 negative blood groups, as this antigen frequently causes blood transfusion reactions. DEA 1.1-negative dogs are considered “universal donors” because their blood does not cause incompatibility reactions in most dogs, regardless of their blood type. It is therefore used specifically in time-critical emergencies.

Horse

A total of seven blood groups are known in horses (A, C, D, K, P, Q, and U). These also carry different cell membrane proteins (=factors: a-i, r-k). Despite the 34 possible combinations of blood group and factor in horses, incompatibilities between donor and recipient blood are less common than in other animals or humans.

The first blood transfusion is usually unproblematic in dogs and horses, as they do not yet possess antibodies against other blood group antigens as long as they have not had contact with foreign blood. An exception are mares that have had a foal with so-called neonatal isoerythrolysis (= destruction of the foal’s red blood cells by the mare’s antibodies). If possible, however, a compatibility test between donor and recipient blood should also be performed during the first blood transfusion in dogs and horses.

A small area of skin on the recipient animal is shaved and disinfected. The donor blood is warmed to body temperature and then administered into the great jugular vein via a special infusion tube with a built-in blood filter.

The rate at which the transfusion is administered depends on the recipient animal’s hydration status, the severity of the anemia, and its general condition. If there is a critical deficiency in circulating blood or fluid volume, the rate is increased. For animals with heart disease or renal failure, a slower transfusion rate is required. The first few milliliters are administered very slowly over 15 minutes. The transfusion then continues for up to four hours. The animal is continuously monitored throughout the process. Heart and respiratory rates are checked regularly for several hours after the transfusion.

Risks of a Blood Transfusion

Transfusion reactions occur in approximately two percent of all blood transfusions. They are therefore rare and often harmless. However, the following reactions may occur during and after a blood transfusion:

• Fever is the most common reaction. It can occur within the first four hours, resolves on its own, and does not require treatment.
• Vomiting can occur if the transfusion is administered too quickly or if the patient is fed before or during the transfusion.
• Hypothermia can occur if donor blood that was previously stored at a low temperature is not warmed sufficiently.
• Shortness of breath and heart failure can occur due to volume overload, which strains the circulatory system, during and up to 24 hours after the transfusion. The transfusion is then stopped immediately. Additionally, diuretics are administered.
• An acute allergic reaction may occur during or in the first few hours after the transfusion. Skin reactions or gastrointestinal disturbances, as well as shortness of breath and anaphylactic shock, may occur. The transfusion is then stopped immediately. Additionally, anti-allergic medications are administered, and if necessary, measures are taken to support circulation.
• If hemolysis (the destruction of red blood cells) occurs, it is accompanied by fever, increased heart rate, shortness of breath, and can progress to shock and blood clotting in the blood vessels. The transfusion is then stopped immediately, and life-saving measures are initiated.
• If an infection occurs due to a blood donation containing pathogens, it is treated depending on the pathogen.

Since it is difficult to store large quantities of blood properly, freshly collected blood from donor animals is usually used. In general, blood units can be stored at 4°C with continuous temperature monitoring for up to 35 days. Many veterinary practices maintain a list of potential donor animals. Since these are often emergencies, owners who can bring their donor animals to the practice quickly and flexibly are needed.

Donor animals must also meet the following requirements:

• Fully grown to middle-aged: dogs and cats over one year old, horses at least three to four years old
• Minimum weight: 20 kilograms for dogs, 4 kilograms for cats
• Healthy (not on medication) and calm temperament
• No history of travel to southern countries
• Regularly vaccinated, dewormed, and, for small animals, parasite prophylaxis
• Never received a blood transfusion

After a general examination and blood test of the donor animal, a compatibility check is performed to ensure the donor and recipient blood are compatible. If so, a small area of skin on the neck is shaved and disinfected for the blood donation. Blood is then collected from the jugular vein into a blood collection bag or, in the case of cats, into a large syringe. The blood donation takes only 15 minutes, though longer for horses due to the volume of blood. The donor animal must remain calm during the procedure. For this reason, a sedative injection is necessary for cats as well as for some dogs. Depending on the size of the recipient animal, the following amounts are collected:

• for dogs and cats: ten milliliters per kilogram of body weight
• for horses: three to six liters

Withdrawing these amounts places little strain on the donor animals. The body replaces the withdrawn blood within a short time. However, you should avoid strenuous activity for your animal for up to 24 hours after the blood donation. Dogs should wear a harness instead of a collar for a few days. The next blood donation may take place no sooner than three months later.

Often, the blood collected from the donor animal is separated into its components by centrifugation immediately after collection. This makes it possible to transfuse only the specific component that the recipient animal is lacking. This prevents volume overload, and the remaining components can be used for other animals.

Whole blood or red blood cell concentrate is used for emergencies involving acute blood loss and in cases of anemia (a deficiency of red blood cells); whole blood is also used in cases of severe thrombocytopenia (a deficiency of platelets). Blood plasma is used for other blood clotting disorders (see relevant article) as well as hypoproteinemia (loss of protein via the kidneys or intestines).