Chapter 15
Feline Donor Selection
Charlotte Russo and Karen Humm
Royal Veterinary College, Queen Mother Hospital for Animals, Hatfield, Hertfordshire, UK
Introduction
The welfare of any blood donor is paramount, therefore careful donor selection and a clear understanding of the required donor criteria are vital. Transfusion medicine comes with risks to both recipients and donors, but with appropriate donor selection and screening these risks can be minimized.
Feline blood products are a precious resource due to their limited availability. Although some feline blood products are now available from commercial blood banks in many parts of the world, they are not yet available everywhere.
Considerations in donor selection
A potential feline donor must meet certain criteria before being considered for blood donation (Box 15.1). Once it is established that a cat matches these criteria, the additional health assessments described below should be performed.
History
A complete history should be taken before enrollment in a blood donor program and repeated prior to any potential donation. The history should uncover any recent illnesses that have either been investigated or might require further investigation before a blood donation is performed. Only once the cat has been cleared of any potential health problems can they donate.
The donor’s travel history should be explored as they might have travelled outside of the country or to an area endemic for transmissible diseases, which should prompt further investigation. United Kingdom (UK) based blood donor programs generally exclude cats that have travelled outside of the UK or Ireland, as they require additional infectious disease screening, which can be costly for the program to perform. Similar restrictions might also be required in other parts of the world.
Cats receiving long-term medications (including non-prescription drugs such as supplements) should be excluded from blood donor programs. Additionally, any donor that has received a course of short-term medications must be healthy for at least 2 weeks after finishing the medication before a donation is performed to ensure there is no trace of the medications in the donated blood and that the donation is considered safe. However, the period of time required between drug cessation and donation might be even longer (particularly when considering depot preparations), therefore advice from the program veterinarian should be requested on a case-by-case basis.
Blood donors should never have received a blood transfusion themselves due to the potential for development of antibodies to the donated erythrocytes, which could theoretically be administered to the recipient. This is true even in cats, which are known to have naturally occurring anti-A and anti-B antibodies, because there is always the risk of undescribed or new blood antigens that could stimulate antibody production.
For many cats, it might be difficult to obtain a complete history as they might have been re-homed by a rescue group, therefore their entire history might not be known. There is little literature to guide veterinarians in the decision of whether to use re-homed animals with an unknown history, thus the decision is ultimately up to the individual program director. These selection guidelines and suggested donor criteria are intended to protect both the donor and recipient, so if the criteria can only be assumed and the suitability of the donor is in question, then the risk outweighs the benefit and the cat should be excluded from the program.
Behavior
Most literature will state that feline blood donors should have an agreeable temperament for easy handling and restraint, but it is more important that their temperament is suitable such that they do not become stressed or unhappy. This ensures feline donor welfare is upheld above all else. Measures should always be taken to ensure feline donor comfort and to minimize levels of stress; the more positive the experience, the more relaxed and cooperative feline donors will be during future donation visits.
Feline pheromone diffusers or sprays, use of the donors’ own blankets, and a quiet relaxed environment can make a great difference in the quality of the visit, as well as promoting a relaxed donation process for the present and any future donations (Figure 15.1).
Figure 15.1 A relaxed feline donor before donation.
Sedation of feline blood donors to achieve blood collection has generally been accepted as a requirement, meaning temperament has only been assessed to feasibly achieve administration of sedation. However, recent advances in the understanding of feline behavior and transfusion medicine have led to unsedated/conscious feline blood donations being safely and successfully performed, with priority given to the donor’s welfare. This advancement has made selecting feline donors based on their behavior and personality, and therefore suitability to join a blood donor program, of more significant value, something that has always been considered a priority when selecting canine blood donors.
The word “donation” signifies a gift given to benefit a cause, which implies a voluntary act. Many ethical concerns have been raised regarding animal blood donations and the issue it raises regarding consent. Canine donors appearing to be at ease and with a willingness to cooperate without undue restraint should be deemed as consenting with a degree of voluntariness assumed (DeLuca et al. 2006). Any dog’s behavior that does not fit with this statement should be recognized as unwillingness to donate and they should not participate. The recognition of this behavior as a form of consent with canine donors should also be adopted for cats whenever possible as this level of behavioral assessment will ensure higher standards of care and treatment of feline donors.
Weight
Donors should be of normal body condition with no recent episodes of unexplained weight loss. The World Small Animal Veterinary Association (WSAVA) describes the ideal body condition of cats as palpable ribs with minimal to slight fat coverage, a noticeable waist, and a minimal to absent abdominal fat pad (Figure 15.2). The ideal feline donor is a large cat weighing at least 5 kg (lean body mass), although cats weighing a minimum of 4 kg can be used as donors due to the use of open blood collection systems that allow the volume of blood collected to be tailored according to the donor’s weight. If the blood is being donated for a specific patient, then the recipient’s packed cell volume (PCV) and body weight should be considered in order to determine the desired volume of blood required for transfusion. This enables smaller donors to be reserved for smaller recipients. It is important to note that larger cats are likely to experience fewer side effects associated with blood donation, so whenever possible a cat of at least 5 kg is considered the most suitable (Barfield and Adamantos 2011).
Figure 15.2 World Small Animal Veterinary Association feline body condition score from the Global Nutrition Committee Toolkit.
(Courtesy of the World Small Animal Veterinary Association.)
Donor health assessment
A thorough health assessment by a veterinarian should be performed on all feline blood donors prior to joining a donor program to determine if they are of optimum health and that it is safe for them to donate blood (Figure 15.3). This will also ensure that their donated blood will be safe and of suitable quality to transfuse to a recipient (Table 15.1).
Figure 15.3 Feline donor health assessment.
Table 15.1 Feline blood donor health assessments to be performed prior to each blood collection
| Assessment | Action |
| Cardiac auscultation | Rate and rhythm: compare to previous recordings Presence or absence of a heart murmur or gallop (Barfield and Adamantos 2011) |
| Body condition | Suitable body condition score Suitable weight: compare with previous measurements (Helm and Knottenbelt 2010) |
| Dermatologic | No obvious wounds or injuries Pyoderma should delay a donation due to potential bacterial contamination of collected blood Evidence of ectoparasites should also delay donation accordingly (Wardrop et al. 2005) |
| Abdominal palpation | Evidence of abnormality or discomfort Bladder size: if large/full ensure no evidence of urinary tract obstruction |
| Vital signs | Measurements within normal limits Compare with previous recordings |
| Respiratory system | Rate and effort Abnormalities during lung field auscultation |
| Lymph nodes | Ensure lymph node sizes are within normal limits |
| Eyes | No discharge or abnormalities |
| Mobility | Ambulatory without lameness |
| Temperament | Ensure there is no evidence of distress or pain |
| Oral cavity | Mucous membrane color Capillary refill time Presence of dental or periodontal disease |
The donor’s well-being should always be the priority; if any potential problems are noted during a health assessment, the donation should not take place and the problem(s) should be fully investigated. These health assessments must be performed prior to each donation so that any subtle clinical signs of illness or infectious disease can be noted, thereby minimizing the risks to the donor and optimizing the health of the recipient. Owners of volunteer donors should also be advised to report any illness that might occur 48 hours post donation, in case early symptoms of illness were not detected or were not present at the time of their pre-donation health assessment.
All health assessments, including temperature, heart/pulse rate, and respiration rate (TPR), should be recorded in the blood donor’s record for future reference and comparison, along with their body weight and hemoglobin or PCV measurements. Cats known to have any form of ongoing illness should not be considered for blood donation, especially those with heart or kidney disease, due to the potential for exacerbating their disease (Côté et al. 2004). This is also the reason a 1–8-year-old age limit is used, as there is an increased potential for these diseases to be present in a more senior cat.
Annual blood tests
In addition to a health assessment, screening blood tests should be performed prior to enrolling cats in the donor program and then repeated on an annual basis for the length of the cat’s time in the donor program. A routine complete blood count (CBC) and serum biochemistry should be performed to assess general health. Any irregularities should be investigated and re-tested as necessary before a donation is performed. Obtaining (and recording) a suitable PCV measurement prior to each donation is vital, as this ensures that any donated blood has adequate red blood cells (RBCs) for effective transfusion. More importantly, it also protects the donor from anemia secondary to donation (Wardrop et al. 2005). A PCV of at least 30% is required, although 35% and above is ideal (Schumacher 2012). Close monitoring of the donor’s PCV is recommended to ensure any negative patterns are noticed, allowing steps to be taken to encourage improvement in PCV. For example, this might involve increasing the length of time between donations. Some blood donor programs also provide iron supplementation for their cats to help reduce the time taken to recover their lost iron and hemoglobin.
Echocardiography
Heart murmurs were detected in 22 of 103 (21%) overtly healthy cats that were candidates for blood donation (Côté et al. 2004). Subsequent echocardiography revealed that many of these murmurs were caused by structural heart disease, which automatically excluded the cats from the blood donor program. Clearly, a large proportion of overtly healthy cats have heart murmurs and potential heart disease. Likewise, many cats with heart disease do not present with heart murmurs, therefore the presence of underlying heart disease cannot be excluded just because a heart murmur is not present (Paige et al. 2009).
An echocardiogram is recommended in all feline donors when a murmur has been detected. Some blood donor programs also perform echocardiograms on all feline donors, with or without the presence of a murmur, prior to enrollment on the program due to the potential for structural heart disease and the perceived increased risk associated with blood donation in cats with heart disease (Figure 15.4). It is recommended that cats with structural heart disease should not be considered for blood donation. Providing a free echocardiogram for all potential feline donors is also a sizeable incentive for owners considering offering their cat as a potential donor.
Figure 15.4 Echocardiogram being performed on a feline donor.
Feline blood types
Knowledge of feline blood types, blood typing procedures, and their interpretation is imperative for effective and safe feline transfusions. Unlike dogs, by 6–8 weeks of age and without prior sensitization from a blood transfusion, cats can produce alloantibodies against the type A or B RBC antigens they lack (Bucheler and Giger 1993). These antibodies are referred to as “naturally occurring” alloantibodies and have the potential to cause serious and sometimes fatal transfusion reactions. Their presence necessitates AB blood type matching of the recipient and donor cat prior to all blood transfusions to ensure that type-specific transfusions are always achieved and the risks of transfusion reactions are minimized.
AB blood group system
Feline blood types are classified according to the AB blood group system. It is the most widely recognized blood group system in cats and comprises three blood types: A, B, and AB. Due to the presence of naturally occurring alloantibodies, cats do not have a universal blood type. The frequency and amount of naturally occurring alloantibodies varies among the blood types. Awareness of them is useful for understanding the importance of type-specific transfusions in cats due to the high risk of a transfusion reaction occurring if an unmatched transfusion is performed (Knottenbelt et al. 1999).
Type A has consistently been the predominant feline blood type in domestic cats worldwide, while the frequency of type B has shown variation with geographical location and among certain purebred cats. Type AB is consistently a rare blood type (Knottenbelt 2002). Some breeds have a higher prevalence of certain blood types. For example, British Shorthairs, Turkish Vans, and Turkish Angora cats have a high prevalence of type B, whereas Siamese and Maine Coons have a high prevalence of type A. Importantly, neither the breed nor geographical origin of the cat should preclude performing blood typing (Forcada et al. 2007).
All type B cats have high levels of strong anti-A antibodies, meaning if they are transfused with type A blood it can result in a potentially fatal reaction and rapid intravascular destruction of the transfused blood (Stieger et al. 2005). However, the frequency of type A cats with anti-B antibodies seems to show some geographical variation. For example, all type A cats had a level of anti-B antibodies capable of at least microscopic agglutination of type B cells in a United States (US) based cat population (Bucheler and Giger 1993). In contrast, 28% of type A cats did not have detectable anti-B antibodies in a UK-based cat population (Knottenbelt et al. 1999); the cats that did possess anti-B antibodies had generally higher titer levels than cats in the US.
Overall, in comparison to the anti-A antibodies found in type B cats, the anti-B antibodies found in type A cats are relatively weak and cause milder transfusion reactions, therefore a transfusion of type B blood to a type A cat is likely to result in the premature removal of most of the transfused red cells after 5–7 days (Giger and Bucheler 1991), but not the severe and often fatal reactions that are noted in type B cats administered type A blood.
Type AB cats do not possess any alloantibodies because of the presence of both antigens on the surface of their RBCs (Forcada et al. 2007). Ideally, AB cats would receive a transfusion of AB blood, but due to the rarity of this blood type it is unlikely that an AB donor would be available. It is therefore recommended that these cats receive type A blood, with the understanding that it might cause minor incompatibility reactions due to the presence of anti-B antibodies in the plasma (Schumacher 2012).
Mik antigen
A relatively new RBC antigen called Mik has been discovered at the University of Pennsylvania (Weinstein et al. 2007). A study was conducted to investigate several incompatible crossmatches between donors and a cat (named Mike) that were matched by type. The findings suggested the presence of an alloantibody produced against a new common RBC antigen, termed Mik. It is estimated that approximately 94% of domestic shorthair cats have the Mik antigen, and the naturally occurring anti-Mik alloantibody that the three donors possessed is rare (Weinstein et al. 2007). Currently, screening for the Mik blood type is not available, therefore it has been suggested that crossmatching should be performed prior to all feline blood transfusions, even first transfusions that are type-specific, to avoid potential transfusion reactions due to this antibody (Schumacher 2012).
Blood-typing tests
While blood typing can be performed at commercial laboratories, feline blood typing kits for in-hospital use are widely available, relatively inexpensive, and quick and effective for determining type A, B, and AB cats. However, some of these tests have difficulty determining the AB blood type (Steiger et al. 2005). The principle of blood typing is the visible agglutination of RBCs when exposed to the known antibodies to A and B antigens, therefore all blood typing tests require an EDTA anti-coagulated whole blood sample.
The University of Pennsylvania performs slide and tube blood agglutination typing tests, which are very reliable and considered the gold standard. They are often used when there are concerns with the accuracy of a blood typing result or when a practice is unable to perform or interpret in-hospital blood typing. The two most common and reliable commercially available blood typing kits are the Rapid Vet-H Feline card system (DMS Laboratories, NJ) and the Quick test A + B migration paper strip immunochromatographic cartridge (Alvedia, Limonest, France).
Card agglutination test
The Rapid Vet-H card system relies upon a visible agglutination reaction. There are three wells on these cards: the first is an auto-agglutination saline screen that does not contain any reagents, the second is labeled type A and contains anti-A antibodies, while the third well labeled type B contains Triticum vulgaris lectin, which specifically agglutinates type B erythrocytes (Andrews et al. 1992; Stieger et al. 2005).
The EDTA blood sample is mixed in each well with the supplied diluent and agitated gently for 2 minutes, after which time the wells are visually inspected for signs of agglutination. Agglutination solely in the type A well indicates type A blood (Figure 15.5), whereas agglutination solely in the type B well indicates type B blood (Figure 15.6). Agglutination in both wells indicates type AB blood. There have been some inaccurate results reported when both the A and B wells agglutinate, so it is recommended that if this occurs, the test should be repeated at an external laboratory in order to confirm the result (Barfield and Adamantos 2011).
Figure 15.5 Card agglutination test showing a type A blood result.
Figure 15.6 Card agglutination test showing a type B blood result.
Some cats might exhibit auto-agglutination (e.g., cats with immune-mediated hemolytic anemia), which will be evident if there is agglutination present in the auto-agglutination saline screen well. It will not be possible to definitively type auto-agglutinating cats using the rapid Vet-H card system without first washing the RBCs before performing the test (Box 2).
Immunochromatographic test
The immunochromatographic test is based on the migration of RBCs on a specially treated membrane on a paper stick (Figure 15.7). Antibodies specific to the A and B antigens are incorporated on the membrane in different 1-mm strips on the stick. A RBC suspension is allowed to migrate up the membrane and the blood type is determined by the presence of a red band at one or two of these strips. A red control band located at the uppermost part of the strip has to appear to confirm the test has run successfully. If it is not present then the test must be repeated.
Figure 15.7 Immunochromatographic cartridge blood typing kit.
If the cat is type A then two red lines will appear on the strip adjacent to the letters A and C (Figure 15.8). If the cat is type B then two red lines will appear on the strip adjacent to the letters B and C. If the cat is type AB then three red lines will appear on the strip adjacent to all three letters A, B, and C (Figure 15.9).
Figure 15.8 Immunochromatographic cartridge test showing a type A blood result.
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