Urs Giger,     Philadelphia, Pennsylvania

Canine Blood Types

Blood types are genetic markers on erythrocyte surfaces that are antigenic and species specific. A set of blood types of two or more alleles makes up a blood group system. Dogs have more than a dozen blood group systems known as dog erythrocyte antigens (DEA); however, there is no DEA 2 blood group. Canine erythrocytes are either positive or negative for a blood type (e.g., DEA 4 positive or negative), and these blood types are thought to be inherited codominantly. In the DEA 1 system, which represents an exception, DEA 1.1 (A1) and 1.2 (A2) are apparently allelic and there even may be a DEA 1.3 (A3). Thus a dog can be DEA 1.1 positive or negative and DEA 1.1–negative dogs can be DEA 1.2 positive or negative. Recent studies by the author’s laboratory indicate that the DEA 1 blood group may be a continuum from negative, weak, moderate, to strongly positive rather than having two or three blood types.

The clinically most important canine blood type is DEA 1.1. DEA 1.1 (A1) elicits a strong alloantibody response after sensitization of a DEA 1.1–negative dog by a transfusion and thus can be responsible for a transfusion reaction in a DEA 1.1–negative dog previously transfused with DEA 1.1–positive blood. Transfusion reactions against other blood types rarely have been described. They include reactions against the DEA 4, Dal, and another common red cell antigen, and other clinically important blood types may be found in the future. No reagents currently are available against many antigens, and additional blood types continue to be recognized.

Only limited surveys on the frequency of these blood types have been reported (Web Table 26-1), which suggest possible geographic and breed-associated differences. For instance, all typed Saint Bernard and most golden retriever dogs tested are apparently DEA 1.1 positive. Some of the blood types are seen rarely (DEA 3), whereas others occur commonly (DEA 4). In Japan additional blood group systems have been proposed, but their associations to the DEA systems and their clinical importance have not been documented. Recently, an apparently new common red cell antigen has been identified that seems to be missing in some dalmatians; therefore it is named Dal red cell antigen.

Strongly antigenic blood types are of great clinical importance because they can elicit a potent alloantibody response. These alloantibodies may be of the immunoglobulin G (IgG) or IgM class and may be hemagglutinins or hemolysins. Based upon experimental and clinical data, dogs can become sensitized after receiving a mismatched transfusion (i.e., a blood unit positive for one or more blood types not found on the recipient’s red blood cells) but not by pregnancy.

There are no clinically important, naturally occurring alloantibodies (also known as isoantibodies) present before sensitization of a dog with a transfusion. Sensitizing dogs in experimental studies in the 1950s led to the documentation of some transfusion reactions caused by blood group incompatibilities and to the characterization of new blood types. Clinically the most antigenic blood type in dogs is the DEA 1.1. Transfusion of DEA 1.1–positive cells to a DEA 1.1–negative dog invariably elicits a strong alloantibody response. After a first transfusion, anti-DEA 1.1 antibodies develop after more than 4 days and may cause a delayed transfusion reaction. However, a previously sensitized DEA 1.1–negative dog can develop an acute hemolytic reaction after transfusion of DEA 1.1–positive blood. Transfusion reactions also may occur after a sensitized dog receives blood that is mismatched for a red blood cell antigen other than DEA 1.1. For instance, a whippet developed an alloantibody against a common red blood cell antigen, resulting in a general incompatibility with any donor except a littermate. Similarly, a dog with DEA 4–negative blood, another common antigen, showed an acute hemolytic transfusion reaction after receiving a second DEA 4–positive blood transfusion. However, in most cases the incompatible blood type has not been determined. Because administration of a small (<1 ml) amount of incompatible blood can result in life-threatening reactions the practice of giving small “test volumes” of donor blood to assess blood-type compatibilities is unacceptable. In contrast, pregnancy does not cause sensitization because of a complete placenta in dogs and does not induce alloantibody production; thus dogs with prior pregnancies can be used safely as donors.

Canine Blood-Typing Procedure

Because of the strong antigenicity of DEA 1.1, typing of donors for DEA 1.1 is recommended. Whenever possible, the recipient also should be typed to allow the use of DEA 1.1–positive blood for DEA 1.1–positive recipients. Canine blood typing is based generally on serologic identification by agglutination reactions. Originally serum from sensitized dogs has been used for typing, but such polyvalent alloantibodies vary from batch to batch, may require Coombs’ reagent to show agglutination, and may not be available always and are therefore not optimal. Recently, monoclonal antibodies against DEA 1.1 have been developed at Kansas State University and at the University of Lyon. The gel column technology, widely used in human blood banking, was found to be an excellent standardized laboratory method (DiaMed), but unfortunately the company was sold and no longer is producing veterinary products. A blood typing card has been available since the mid-1990s as a simple in-practice kit to classify dogs as DEA 1.1 positive or negative, although the design of the card and its wells has been changed over the years. Based on limited data this card may give a weak positive agglutination reaction with DEA 1.2–positive red cells. A cartridge became available in the mid-2000s from Alvedia DME that relies on a standardized simple chromatographic technique and not agglutination. This method is also now available as a strip technique for larger laboratories. Another cartridge with a similar strip technique has just been introduced. Moreover, a third cartridge method in which blood flows through the cartridge also should be available in the future (Abaxis).

Caution should be exercised whenever the patient’s blood is autoagglutinating or has a low hematocrit (<10%). If autoagglutination is not too severe, it does not appear to affect the cartridge technique because only free red cells are moving up the strip. Clinicians should check for autoagglutination of blood with buffer/saline on a slide or the card. Autoagglutinating blood may be first washed three times with saline to overcome the apparent autoagglutination similar to the Coombs’ and crossmatch tests performed within tubes. However, if autoagglutination after three washes persists at more than 1+, it is considered to reflect true autoagglutination, which precludes typing (as well as Coombs’ testing and crossmatching), because it always looks like DEA 1.1–positive blood. In such circumstances, DEA 1.1–negative blood should be used, until the patient does not agglutinate anymore and can be retyped. DEA 1.1–positive blood from anemic animals may not agglutinate when exposed to the DEA 1.1 or other reagents because of the prozone effect. In these cases some of the patient’s plasma may be discarded before applying a drop of blood onto the card. Finally, recently transfused dogs may display a mixed field reaction, with only the transfused or recipient cells agglutinating.

Some veterinarians recommend using exclusively canine donors that are negative for all testable DEAs except DEA 4 (>98% of dogs are DEA 4 positive) to prevent sensitization against these blood types. However, the author does not support the routine typing for other blood types than DEA 1.1 for many reasons. This protocol would eliminate unnecessarily many active and potential donors. Based upon published blood type frequencies less than 1 in 10 dogs would be acceptable donors. This extended blood typing protocol also would be cost prohibitive because many dogs would need to be typed in order to find a negative dog. The typing reagents beyond DEA 1.1 are not readily available; typing methods are not well standardized for additional blood groups and may not give clear typing results. Generally, humans are typed only for the ABO and Rh blood group systems, although more than 2 dozen other blood group systems are known (plus ~100 high-frequency red cell antigens). Typing for more than DEA 1.1 does not eliminate the need for crossmatching after the first transfusion. Crossmatching also may identify incompatibilities against yet unknown types. No supporting published clinical reports state that transfusion reactions could be reduced substantially or explained by extended blood typing.