Blood transfusions in small animal medicine have become more common and are now an integral part of advanced treatment. Often, the indication for blood transfusion occurs in the emergency or surgical setting. Situations that may require transfusion include life-threatening anaemia from acute haemorrhage, haemolysis, problems due to drugs or toxins, immune-mediated diseases, severe non-regenerative conditions and neonatal isoerythrolysis (NI), among others.
Advances in critical care medicine have moved transfusion medicine to the forefront of management in such cases. To ensure efficacious and safe transfusions, it is important to perform blood typing and cross matching, as incompatible transfusions can be life threatening.
This article explores the different blood group categories for dogs and cats, and describes blood typing, cross matching, transfusion reactions and their prevention.
Canine and feline blood groups
Blood groups are defined by inherited antigens on the surface of red blood cells (RBCs). They are important in transfusion medicine because of the risk of haemolytic reactions. Such reactions occur when there are antibodies directed against a blood group antigen (Kristensen and Feldman, 1995).
Canine blood groups
There are seven recognized canine blood groups categorized under the Dog Erythrocyte Antigen system: DEA 1.1, 1.2, 3, 4, 5, 7, and Dal (Iazbik et al, 2010). Blood group systems are two allelic, which means a dog can be positive (presence of an antigen) or negative (absence of antigen) for that particular blood type (Giger et al, 2005).
There are no naturally occurring alloantibodies to DEA 1.1 or 1.2, so these antigens will not cause an acute reaction during a recipient's first transfusion. However, if a DEA 1.1-negative dog receives a transfusion from a DEA 1.1-positive dog, anti-DEA 1.1 antibody formation will cause delayed haemolysis within 1–2 weeks (Figure 1). On a subsequent exposure to DEA 1.1-positive blood, an acute haemolytic transfusion reaction will occur, with destruction of all transfused RBCs within 12 hours (Giger et al, 1995).
The situation is similar for sensitization to DEA 1.2, except that the reaction is less severe, with destruction of transfused RBCs within 24 hours (Giger et al, 1995).
NI occurs when a sensitized DEA 1.1-negative female mates with a DEA 1.1-positive male (this only happens if the female has already received a DEA 1.1-positive blood transfusion). Inheritance is autosomal dominant, therefore the likelihood is that the puppies will be DEA 1.1-positive and have haemolytic disease (Hale, 1995; Bücheler, 1999).
The prevalence of transfusion reactions provoked by other DEA groups is not known, but has not been proven to be clinically relevant (Lanevschi and Wardrop, 2001).
Although most dogs are positive for DEA 4, this antigen does not cause haemolysis and has minimal transfusion significance (Hale, 1995; Kristensen and Feldman, 1995).
A new antigen known as ‘Dal’ has been described. This antigen has no relation to known DEA antigens, and it appears to be lacking only in some Dalmatians. After transfusion sensitization, development of anti-Dal alloantibodies may result in haemolytic transfusion reactions, if Dal-positive blood products are subsequently used. Additionally, Dal antigen appears to be found in very high frequency in dogs other than Dalmatians (Hale, 1995; Blais et al, 2007).
Feline blood groups
In cats, a well established AB blood group system, based on naturally occurring alloantibodies, has been described (Andrews et al, 1992).
The AB system, characterized by Auer and Bell (1981), consists of three blood types: A, B and AB. The incidence of these blood types varies among cat breeds and geographical locations. The allele for group A is dominant over that for group B, and thus cats expressing the group A phenotype have a homozygous (A/A) or heterozygous (A/B) genotype, whereas cats expressing the group B phenotype are invariably homozygous for the B allele (B/B). In addition to the A and B phenotype, a small proportion of cats express both A and B antigens on the erythrocyte membrane, presenting an AB phenotype. These AB cats are assumed to have an A/B genotype but with a third allele, which prevents the normal A dominance from being expressed (Knottenbelt, 2002).
There is no universal donor because, unlike dogs, cats have naturally occurring alloantibodies and no null type. Therefore, RBC incompatibility reactions will occur in first-time recipients (Feldman, 2000). The reaction is typically peracute and, sometimes, fatal at the beginning of a transfusion of type A or AB RBCs to a type B recipient, with fever, jaundice and destruction of transfused RBCs in 24 hours (Feldman, 2000). Delayed haemolysis occurs in type A recipients receiving type B or AB RBCs, and acute reactions may occur due to anti-A antibodies in type B donor plasma (Figure 1) (Knottenbelt, 2002).
Type AB cats are universal RBC recipients but are also at risk of incompatibility reactions from donor plasma antibodies (so-called ‘minor incompatibility reactions’). If a large volume is needed for transfusion in type AB cats, washed RBCs can be used (Knottenbelt, 2002).
More recently, Weinstein et al (2007) reported a blood group antigen and clinically relevant alloantibody distinct from the AB blood group system that the researchers named ‘Mik’. Their fndings show that in Mik antigen negative cats, anti-Mik is a naturally occurring alloantibody, similar to anti-A and anti-B present in type B and type A cats.
NI
NI is believed to be a major cause of Fading Kitten Syndrome. Neonatal kittens acquire maternal antibodies via colostrum during the first day of life, which leads to intra- or extra-vascular haemolysis in kittens with a blood type incompatible with that of their queen. Clinical signs vary from subclinical to peracute signs, including sudden death, failure to thrive, anaemia, jaundice and tail-tip necrosis (Knottenbelt et al, 1999).
Prevention of NI involves avoiding incompatible mates. A simple strategy is to mate type B queens only with type B toms. If incompatible mating occurs, kittens should not be allowed to be nursed by their type B mother for the first 24 hours, which is the duration of time over which absorption of colostral antibodies occurs. A or AB kittens can safely start to receive colostrums or milk from a type A queen at this time. Cord blood can be used to determine the kitten's blood type at birth, or to perform a cross match with serum from the queen (Knottenbelt et al, 1999).
Blood typing and cross matching
Blood typing (methods)
The principle of all veterinary blood-typing methods is a visible haemagglutination reaction between patient RBC surface antigens and known reagent monoclonal or polyclonal antisera. In veterinary medicine, tube, card, and gel column methods are used (Giger et al, 2005, 2007; Stieger, 2005).
Typing cards for canine and feline blood have a lyophilized reagent on the cards that is reconstituted with a diluent before performing the test. The cards contain a patient/donor test area as well as controls. For the dog, DEA 1.1 typing is available, and for the cat, types A, B and AB can be determined. The test can be standardized and adapted to either the clinical laboratory or a point-of-care situation (Giger et al, 2005, 2007; Stieger et al, 2005).
A novel gel column agglutination test is now available for both canine and feline blood typing, which offers an alternative method. The gel column agglutination test uses microtubes that contain reagent, as well as gel particles, that act as a sieve/matrix. The principle of this test is a visible haemagglutination reaction, where unagglutinated cells pass through the gel and pellet at the bottom of the microtube, while large agglutinates remain suspended in the gel (Giger et al, 2005, 2007; Stieger et al, 2005).
The tube test is based on a novel canine blood group classification, which has been proposed by researchers in Japan. However, this new blood-typing classification has not yet been correlated with the DEA system (Bromilow et al, 1991; Hitzler et al, 1993; Giger, 2000; Kaoru and Kyo, 2001). The tube test for cats uses monoclonal antibodies recognizing the feline A and B antigens (Kaoru and Kyo, 2001).
Determining blood types represents an essential process to ensure animals benefit from transfusion support. In the UK, ID-micro typing system gel cards and rapid card agglutination tests for dogs and cats are available. DiaMed, DMS Laboratories and Alvedia provide these gel tests and rapid card tests, commercializing, respectively, DiaMed-ID® Micro Typing System, RapidVet-H® and QuickTest for cats and dogs.
The QuickTest from Alvedia is based on the migration of RBCs on a membrane that has previously been specially treated, under the influence of a buffer flux moving along, due to capillary action.
In dog tests, a monoclonal antibody specific to DEA 1.1 antigen is incorporated in the membrane.This antibody will retain positive DEA 1.1 RBCs. It is characterized by the presence of a red band on the mid portion of this membrane (in front of DEA 1.1 written on the kit). If the dog is DEA 1.1-positive, a red line will appear in front of the DEA 1.1 sign on the test. If the dog is DEA 1.1-negative, no line will appear in front of the DEA 1.1 sign on the test.
In cat tests, two monoclonal antibodies specific to the A and B antigens are incorporated in the membrane. These antibodies will retain positive A and/or B RBCs. It is characterized by the presence of a red band on one or two portions of this strip.
For both tests the red control band, located on the upper part of the membrane (written C on the test) has to appear, ensuring the test has run successfully. If not, the test must be repeated.
Cross matching
Cross-matching tests for anti-RBC antibodies can be made by examining for agglutination and haemolysis. Cross matching is an adjunct to, not a substitute for, blood typing, but it may be the only incompatibility test available.
The major cross matching detects recipient antibodies against donor RBCs. The minor cross matching detects donor antibodies against recipients’ RBCs (Littlewood et al, 2000; Weingart et al, 2004) (Figure 2).
The test is designed to help prevent incompatible RBC transfusions that could lead to immune-mediated haemolytic transfusion reactions. The test end-point is a visible haemagglutination reaction. Donor RBCs are incubated with recipient serum and observed for visible agglutination. If an agglutination reaction is demonstrated, an incompatibility exists and the donor RBCs should not be used for the transfusion. In this situation, the recipient has either a naturally occurring antibody or an induced alloantibody direct against an antigen present on the donor RBCs. If no agglutination is noted, the cross-match is considered compatible and RBCs acceptable for transfusion (Tocci and Ewing, 2009).
Cross matching only identifies alloantibodies already present in the donor or recipient serum. It does not define the blood types of the donor and recipient. It is important to note that a compatible major cross match, minor cross match, or both, does not guarantee normal RBC survival and does not completely eliminate the risk of the transfusion.
Delayed transfusion reactions are caused by production of RBC antibody shortly after a transfusion of the corresponding antigen (3–5 days) (Giger et al, 2005,2007).
The rapid slide test for cats and for dogs is used in an emergency. The tube test for dogs is used if time allows. In both methods either serum or plasma can be used (Littlewood et al, 2000).
Agglutination must be distinguished from rouleaux formation. This is easy to do with strong agglutination but may be difficult with weak agglutination. Microscopically, in aggregates of agglutinated RBCs, the cells are rafted together, randomly oriented and superimposed on each other; in rouleaux, the RBCs are aligned face-to-face and thus appear as ‘stacks of coins’ (Littlewood et al, 2000).
A rapid slide test using diluted RBCs is superior for distinguishing agglutination and rouleaux microscopically and for detecting weak agglutination (Littlewood et al, 2000).
Transfusion reactions
Transfusion reactions are adverse events occurring after, and related to, the administration of blood or blood products. Their effects can be fatal in some cases or may result merely in limited benefits to the recipient. Reactions that occur within 24 hours after administration are termed acute reactions, while those occurring more than 24 hours following transfusion are referred to as delayed reactions. Reactions can be caused by immunological or non-immunological mechanisms (Table 1), but both situations should be rare when a matched transfusion is given and blood has been stored and administered appropriately. Despite this, all patients receiving blood or blood products should be monitored closely during the transfusion period (Turnwald and Pichler, 1985).
| Immune mediated | Non immune | |||
|---|---|---|---|---|
| Immunogen | Clinical signs | Cause | Clinical signs | |
| Acute | Red blood cell (RBC) | Haemolysis (intra or extravascular), fever, anaphylaxis, hypotension, apnoea, shock | Contamination | Sepsis, infection |
| Platelets, white blood cells (WBC) | Fever, emesis | Improper collection | Haemolysis, emesis | |
| Plasma proteins | Urticaria, oedema, pruritus | Volume overload | Oedema, dyspnoea, emesis | |
| Microaggregates | Tachycardia, thromboembolic disease | |||
| Delayed | RBC | Shortened RBC survival neonatal haemolysis | Infected donor | Disease transmission (viral, RBC, WBC parasites) |
| Platelet | Thrombocytopenia | |||
If signs associated with a potential transfusion reaction are seen, the transfusion should be stopped immediately. The type of reaction encountered should then be determined and the appropriate treatment given (Turnwald and Pichler, 1985; Weingart et al, 2004).
Vital signs and behaviour should be recorded. Plasma and urine can also be evaluated for the presence of haemoglobin. Vomiting may occur as a non-specific finding, but has also been reported when blood is administered too rapidly, and in association with haemolysis (Weingart et al, 2004).
Immunological acute haemolytic anaemia arises when alloantibodies in the recipient's plasma destroy transfused erythrocytes. Acute hypersensitivity reactions are mediated by immunoglobulin E (IgE) antibodies and arise due to recipient antibody to foreign proteins given in the transfusion. Recipient antibodies against donor platelets, or white blood cells, can result in self-limiting, febrile, non-haemolytic reactions. Pyrexia can also be seen with haemolysis or sepsis. Delayed immunological haemolytic anaemia can arise from incompatible transfusions and in NI (Weingart et al, 2004).
Non-immunological transfusion reactions may be due to abnormal handling or blood storage before transfusion, leading to RBC haemolysis or bacterial contamination. Sepsis can induce non-immunological haemolysis in the patient (Weingart et al, 2004).
Rapid blood transfusion can lead to circulatory overload, particularly in cats with renal or cardiac insufficiency. Signs include dyspnoea and tachypnoea and can progress to pulmonary oedema. Management involves cessation of the transfusion, diuretic treatment and oxygen support (Weingart et al, 2004).
Citrate in blood products chelates calcium and, following transfusion, the citrate usually undergoes rapid hepatic metabolism. However, in patients with hepatic disease, hypocalcaemia can develop due to citrate overload, with rapid administration of blood. Muscle tremors and cardiac abnormalities may be seen and calcium treatment is required (Weingart et al, 2004).
The administration of cold blood products can lead to hypothermia, particularly in young animals, and this can be avoided by pre-warming the blood before transfusion (Weingart et al, 2004).
Non-specific clinical signs that may occur with an acute immunological reaction to a transfused blood product are (Knottenbelt and Helm, 2010):
Preventing transfusion reactions
Transfusion reactions can be prevented by the administration of compatible blood. It is essential to monitor the receiver before, during and after transfusion, and assess the attitude, heart and respiratory rate, state of the mucous membranes, temperature and urine colour (Chiaramonte, 2004).
During the first 20 minutes of transfusion, the rate of administration should not exceed 0.25 ml/kg/h and the mentioned parameters should be reviewed every 5 minutes (Chiaramonte, 2004). If there is no evidence of change, the rate of infusion may be increased, never failing to monitor these parameters. The packed cell volume should be repeated 1–2 hours after the transfusion, as well as the evaluation of the presence of haemolysis. The patient should continue to be monitored during the next 24 hours (Prittie, 2003; Chiaramonte, 2004).
In patients with multiple transfusions, blood from different donors should be used (Prittie, 2003). Non-immunological reactions may also be avoided by (Littlewood et al, 2000; Prittie, 2003; Haldane et al, 2004; Bracker and Drellich, 2005):
To avoid transfusion reactions and complications it is important to (Harrell and Kristensen, 1995):
Nursing care in blood transfusions
Veterinary nurses have the responsibility to monitor patients and recognize any transfusion reaction; it is, therefore, important to know such reactions and constantly monitor various parameters. It is also necessary to assess the value of the haematocrit, before and after the transfusion, as well as the presence or absence of haemoglobin in urine (Feldman, 2000).
The skin must be prepared aseptically for intravenous placement and the equipment verified before proceeding with the transfusion. During transfusion, the veterinary nurse should check for peripheral oedema, assess the degree of hydration and make sure that the fluid is being infused without problems. In small animals, with little weight, the infusion rate is so slow and must be checked constantly to determine whether the fluid is flowing or if the catheter is obstructed.
Blood and blood products can be administered safely via certain types of infusion pump or syringe driver. Some infusion pumps are not recommended because they have pumping mechanisms that will damage RBCs. The veterinary nurse must monitor the patient's cardiovascular system every 5 minutes for the first 30 minutes during transfusion, evaluating the pulse (frequency, speed and strength), mucous membrane colour, capillary refill time, and must auscultate the patient (to identify any arrhythmia). After the first 30 minutes monitoring can decrease to every 15– 30 minutes if there are no signs of transfusion reaction. Regarding the respiratory system, it is important to assess the respiratory rate and to auscultate the chest (to identify pulmonary oedema). The temperature must be constantly monitored, as well as the demeanour. Urinary frequency and any change in the appearance of urine should be recorded (Lane and Cooper, 2003).
In the presence of any change in vital signs, biochemical parameters or patient's demeanour, which may be indicative of transfusion reaction, the transfusion should be stopped immediately and the veterinary surgeon informed. It is important to keep a catheter open for emergency cases (Feldman, 2000).
In a severe peracute reaction it is important to:
If hypotension is suspected, blood pressure should be assessed; if arrhythmias are present or there is a high risk of occurrence, continuous electrocardio-graphic monitoring should be carried out, if possible.
Interruption of a transfusion may violate the ‘4 hours rule’; this could be acceptable as long as care is taken not to contaminate the transfusion during set up, and, in case of doubt, it is preferable to waste a blood product. Once it has been established that the patient does not present any sign of reaction the veterinary surgeon can decide when the transfusion should be restarted (Feldman, 2000).
After transfusion, the patient should continue to be monitored, as some patients do not manifest symptoms until some hours later. It is impotant to constantly monitor the patient during and after the procedure so that any change in the patient can be detected quickly, allowing action to be taken efficiently, and consequently ensuring the success of the transfusion and a favourable clinical outcome for the patient.
Conclusion
Optimizing patient safety in veterinary transfusion medicine is multifaceted. It involves not only using high-quality blood components, but also assuring the integrity of the transfusion process from donor collection through post-transfusion evaluation.
The purpose of blood typing and cross matching is to prevent transfusion reactions. These types of reactions can be life threatening. The transfusion needs to be in such a way as to ensure efficacy and safety. As veterinary transfusion medicine continues to advance, knowledge of all processes and methods is mandatory to improve patient safety. Furthermore, the occurrence of adverse reactions should be documented and investigated.
All patients should be monitored during and post-transfusion, with vital signs and packed cell volume checked before and after transfusion. The transfusion should be stopped immediately if the patient shows any signs of transfusion reaction.
Monitoring is very important, allowing detection of any change in the attitude of the animal and signs of transfusion reactions. The constant monitoring of the animals is a benefit for the success of the transfusion. A clear understanding of how to avoid and/or manage transfusion reactions is vital.