Anemia is one of the most common clinical problems. Although anemia is a feature of many diseases, it is often mild, well tolerated, and corrected by treating the underlying disease. However, certain diseases primarily affected the hematologic system and result in severe anemia due to hemorrhage, hemolysis, and impaired hematopoiesis. Depending on the cause, these anemias may respond well to specific treatments. Often the removal of a triggering agent and toxin is all what has to be done. Infectious cytopenias are commonly associated with infectious diseases, and thus antimicrobial and antiparasitic drugs are often effective. Local hemostasis may stop further hemorrhage. Bleeding caused by anticoagulant rodenticide poisoning responds well to vitamin K therapy. Dogs with immune-mediated thrombocytopenia or hemolysis are treated with immunosuppressive agents. Most difficult is the treatment of non-regenerative anemias, as there are only limited tools to stimulate the bone marrow to produce red blood cells; currently there is only human recombinant erythropoietin available to stimulate erythropoiesis in patients with renal failure, but adverse reaction to the human product have been observed. In case of severe anemia animals will benefit from transfusion therapy. Transfusion therapy has taken an increasingly important role in the life support of animals.

Transfusions are indicated for anemia, coagulopathy, and rarely for thrombocytopenia/pathia, hypoproteinemia, and other conditions. Fresh or stored whole blood, packed red cells, and fresh frozen plasma are the commonly used blood components in veterinary practice. Fresh whole blood contains all components of blood, but specific blood component therapy for each indication provides the most effective and safest support and allows optimal use of every blood donation. Blood components are prepared from a single donation of blood by simple physical separation methods such as centrifugation; thereby, fresh whole blood can be separated into packed red cells, platelet-rich plasma or concentrate, fresh frozen plasma, and cryoprecipitate and cryo-poor plasma. However, transfusions depend on the availability of blood donors and bear some risks of infectious disease transmissions and adverse reactions. In order to assure safe and effective transfusions, it is important to carefully select healthy and infectious disease free donors and to transfuse only blood type compatible blood.

Canine blood types

Dogs have at least thirteen blood types known as Dog Erythrocyte Antigens (DEA) 1 through 13 (no DEA 2). The frequency of each blood type may vary considerably between canine breeds, but detailed surveys are not available. There are no clinically significant alloantibodies present prior to sensitization of a dog. 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. Since the DEA systems have not been completely defined, other clinically important blood types may be found.

Blood Type Frequencies in Dogs

*both DEA 1.1 and 1.2 negative dogs

Simple blood typing cards utilizing a DEA 1.1 monoclonal antibody are available for DEA 1.1 typing of dogs (DMS laboratories, New Jersey; Agrolabo, Turin, Italy) and other clinical typing procedures for laboratories are being evaluated. For blood typing EDTA-anticoagulated blood (purple tube) is preferred over other anticoagulants. It is recommended to blood type both patient and donor for DEA 1.1 prior to the first transfusion. Dogs that are DEA 1.1 negative are considered universal blood donors, as DEA 1.1 negative blood from such dogs will not elicit an immune response and DEA 1.1-mediated transfusion reaction in DEA 1.1 negative dogs can be avoided.

Blood crossmatching

Blood crossmatch test detects the serologic (in-) compatibility between the anemic recipient and potential donor, and should be performed if blood typing is not available or prior to any second or subsequent transfusion. Thus, this test looks for the presence or absence of alloantibodies without determining the blood type, and thus it does not replace blood typing. The crossmatching test does require some technical expertise, which may be accomplished through a veterinary laboratory along with the blood typing and is done with EDTA-anticoagulated blood from recipient and potential donor.

 The major crossmatch tests for alloantibodies in the recipient's plasma against donor cells.

 The minor crossmatch tests for alloantibodies in the donor's plasma against recipient's red cells and is of lesser importance since the donor's plasma will be diluted.

 Autoagglutination or severe hemoglobinemia precludes testing. Washing three times blood with physiologic saline may disperse autoagglutination and rouleaux formation.

Interpretation: Since dogs do not have naturally occurring alloantibodies, the initial crossmatch of a dog that has not previously been transfused should be compatible. A compatible crossmatch in a dog does not prevent sensitization against donor cells within 1 to 2 weeks. Thus, a dog that was given a compatible transfusion from a donor earlier may turn out to be incompatible with the same donor 1-2 weeks later.

Blood Sources

 In-house blood donors kept at veterinary hospitals. Most larger veterinary hospitals have permanent blood donors to cover their transfusion requirements or in case fresh whole blood or platelet-rich plasma (concentrate) is needed.

 Voluntary blood donors are usually client or staff owned. The University of Pennsylvania also has developed a voluntary canine blood donor program through breeders and dog owners and has the first animal blood mobile to collect blood in the Philadelphia suburbs, and Penn Animal Blood Bank provides blood banking expertise.

 Commercial canine blood banks in the United States and other parts of the world can ship blood components overnight

Blood donors should be young adult, lean, and good tempered animals, and weigh at least 25 kg for dogs; have no history of prior transfusion; have been regularly vaccinated and are healthy as determined by history, physical examination, and laboratory tests (complete blood cell count, chemistry screen, and fecal parasite examination every 6-12 months) as well as free of infectious diseases (testing depends on geographic area). Generally donors are not splenectomized even in endemic areas for Babesia. Donors should receive a well-balanced, high performance diet, and may be supplemented twice weekly with ferrous sulfate (Feosal, 510 mg/kg), if bled every 4 weeks. Packed cell volume (PCV) or hemoglobin (Hb) of donor should be >40% and >13 g/dl, respectively. DEA 1.1 positive dogs can receive DEA 1.1 positive or negative blood, however, DEA 1.1 negative patients should never receive blood from a DEA 1.1 positive dog. Dogs not previously transfused will generally have a compatible crossmatch, but would likely be sensitized when receiving DEA 1.1 mismatched blood.

Blood Collection

Blood is collected aseptically by gravity or blood bank vacuum pump from the jugular vein over 5 to 10 minute period. Plastic bags (Fenwal) containing citrate-phosphate-dextrose-adenine (CPD-A1) with or without satellite bags for blood component separation are optimal (closed collection system). Large plastic syringes containing 1 ml CPD-A1 or 3.8% citrate per 9 ml blood and connected to a 19 gauge butterfly needle may be used (open collection system, blood should not be stored). Vacuum glass bottles containing acid-citrate-dextrose (ACD) allow rapid collection, but are not recommended because blood components are readily damaged and cannot be separated and stored.

3.8% sodium citrate is the best anticoagulant solution and without preservative can be used to collect blood for immediate transfusion. ACD, CPD or CPD-A1 are commercial anticoagulant preservative solutions that should provide adequate red cell function and viability. CPD-A1 is most commonly used to store whole blood, packed red cells, and plasma components. Heparin is not recommended as an anticoagulant solution.

Maximal blood volume to be donated by a canine donor: 20 ml blood/kg or one regular blood bag unit of 450 ± 45 ml per = 25 kg dog.

Separation and Storage of Blood Components

The separation of blood components from a single donation of blood is performed according to the Technical Manual of the American Association of Blood Banking and does require some expertise and equipment. Blood components are prepared within 8 hours from the time of collection. Blood components that have been warmed to room or body temperature should not be recooled and cannot be stored again. Similarly, partially used or opened blood bags should be used within 24 hours because of the risk of contamination.

INDICATIONS FOR BLOOD COMPONENT THERAPY

Legend: ? = best component, x = other options, FWB = fresh whole blood, SWB = stored whole blood, PRBCs = packed red blood cells, PRP = platelet-rich plasma, FFP = fresh frozen plasma, CRYO = cryoprecipitate

Fresh whole blood (FWB): By definition, this blood product has not been stored, and all blood components (RBCs, platelets, coagulation factors, and plasma proteins) are present and functional. FWB is indicated in anemic patients with thrombocytopenia/-pathia causing severe, uncontrolled or life-threatening bleeding, but could be given to any anemic patient in need of a transfusion.

Stored whole blood (SWB): Whole blood can be stored in a refrigerator at 4^oC for approximately one month when collected in ACD, CPD or CPD-A1. SWB contains RBCs and plasma proteins (albumin and globulins), but not functional platelets, white blood cells, or labile coagulation factors.

Packed red blood cells (PRBCs): PRBCs are separated from plasma by centrifugation at 4^oC. One unit of blood will result in approximately 200-250 ml plasma and 250-300 ml PRBCs with a PCV between 70 and 80%. PRBCs can be stored at 4^oC for approximately one month. PRBCs are the blood component of choice for severely anemic animals to provide additional oxygen-carrying support.

Platelet-rich plasma (PRP): PRP is prepared from fresh whole blood ("light spin" at room temperature) and are usually used immediately after their preparation. The platelet count of PRP is approximately 3 x 10¹¹/unit (unit defined as platelets derived from 1 unit (450 ml) of FWB). PRP is indicated in thrombocytopenic/-pathic animals with uncontrollable, severe or life-threatening bleeding.

Fresh frozen plasma (FFP): FFP is separated from PRBCs, frozen within 8 hours from collection of blood, and can be stored at -30^oC for up to one year. FFP is indicated in the treatment of coagulopathies (e.g., hereditary coagulopathies, liver disease, anticoagulant rodenticide poisoning) and von Willebrand's disease (if cryoprecipitate is not available).

Cryoprecipitate (CRYO): CRYO, prepared from fresh frozen plasma, contains von Willebrand factor, factor VIII, fibrinogen, and fibronectin and is mainly indicated in management of bleeding due to von Willebrand's disease and hemophilia A.

Administration of Blood

For routine transfusion in the treatment of anemia, it is not necessary to warm blood after removal from the refrigerator. Care should be taken to not overheat the blood products while thawing them. Blood components that have been prewarmed cannot be refrozen/refrigerated. Blood bags are connected to blood infusion sets that have an in-line microfilter. A long (85 cm) blood infusion set with a dripping chamber and a short infusion set for small dogs and cats to connect with syringes are available. Use a latex-free infusion set for platelet administration to avoid aggregation. Microfilter with 170µm pores are commonly used to remove clots and larger red cell and platelet aggregates. Finer filters with 40µm pores will remove most platelets and microaggregates. Leukocyte reduction filters (expensive) may be used to decrease adverse reactions to WBC components. Sterility has to be maintained when connecting blood component bag to infusion set and tubing to catheter.

Blood components are best administered intravenously. Ideally, an indwelling catheter (16-22 gauge depending on size of animal) is placed into the jugular vein, but the cephalic or saphenous vein on extremities may also be used. In case an intravenous access cannot be obtained, red blood cells and plasma may be administered by intramedullary (or intraosseous) infusion at the trochanteric fossa (or other site). Avoid concurrent administration of drugs or fluids other than physiologic saline through the same catheter in order to prevent lysis of erythrocytes and blood coagulation.

Rate of transfusion depends on the hydration status, degree of anemia, and general health condition of an animal. Initial rate is slow, starting with 1-3 ml over the first 5 minutes to observe for any transfusion reactions, even with blood typed and/or crossmatched transfusions. In animals with cardiac failure, do not exceed 4 ml/kg/hr. Transfusion of a single bag should be completed within 4 hours.

The transfusion trigger varies widely depending on the rapidity of onset and severity of the anemia as well as clinical signs; there is no specific PCV at which to transfuse, but at a PCV of <15-20% oxygenation of tissues becomes drastically reduced. Volume of blood component to be administered depends on the degree of anemia and the size of the animal.

Volume (ml) of whole blood = 2 x PCV rise desired (%) x body weight (kg),

or in other words,

Administration of 2 ml whole blood/kg body weight raises the PCV by 1%.

PCV rise desired is the aim for PCV after transfusion minus the recipient's actual PCV; this formula assumes that the PCV of the blood bag is >40%. Monitor response to transfusion by obtaining PCV/TP readings prior to, immediately, and 6 and 24 hours post-transfusion, and consider continued blood loss and/or hemolysis.

In thrombocytopenia or thrombopathia, one unit of PC, PRP or FWB will increase the platelet count by 10,000/µL in a recipient weighing 30 kg. In animals with serious or life threatening bleeding, the platelet count should be increased to above 40,000/µL. Platelet counts are monitored prior, 1 hour, and 24 hours after platelet transfusion.

In coagulopathies and von Willebrand's disease, FFP at 610 ml/kg is an initial dose to stop bleeding or avoid excessive bleeding during surgery. In some cases, larger volumes and repeated administration of FFP may be needed to control bleeding. Cryoprecipitate at a dose of 1 CRYO unit/10 kg or 1-2 ml/kg body weight twice daily is ideal to treat hemophilia A and von Willebrand's disease. Plasma support should be provided for an additional 1-3 days after the bleeding has been controlled to allow for healing and prevent rebleeding.

Complications of Transfusions

While transfusion of blood and its components is usually a safe and temporarily effective form of therapy, there is always a risk for potential hazards. Adverse reactions usually occur during or shortly after the transfusion and can be due to any component of whole blood. Most transfusion reactions can be avoided by carefully selecting only healthy donors, using appropriate collection, storage, and administration techniques, performing blood typing and crossmatching, and administering only needed blood components. The most common clinical sign of transfusion reaction is fever, followed by vomiting and hemolysis. Hemolytic transfusion reactions can be fatal and are, therefore, most important, while fever and vomiting are usually self-limiting.