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Transfusion medicine refers to the administration of blood or its components to treat critically ill patients or support animals undergoing anesthesia for surgical or other procedures. The use of blood products in veterinary medicine has increased over the years, with component therapy becoming more widely available for targeted treatment of specific conditions. Component therapy benefits patients by providing them with only the deficient blood components they need, while minimizing the risk of adverse effects associated with the unnecessary transfusion of other elements. It also promotes better stewardship of a limited resource that is derived from donor animals. Commonly available blood products include packed red blood cells, fresh frozen plasma, frozen plasma, cryoprecipitate, platelet concentrates, and canine albumin.
At the most fundamental level, the indication for transfusion of red blood cells is to treat anemia, with the ultimate goal of improving oxygen delivery to tissues. However, the decision to transfuse should be based on how the patient is responding to their anemia rather than on a specific packed cell volume (PCV). Patients with chronic anemia often develop adaptive responses, such as increased cardiac output and increased 2,3-diphosphoglycerate, which enhance oxygen off-loading to tissues and allow them to better tolerate anemia. In contrast, acutely anemic patients are often more clinically affected and unstable, even with smaller decreases in PCV. Clinical signs that should prompt consideration of transfusion include weakness, collapse, altered mentation, tachycardia, tachypnea, hypotension, and hyperlactatemia. A more liberal transfusion threshold may also be appropriate in anemic patients with underlying cardiac or respiratory disease, increased oxygen demand (e.g., sepsis), or those undergoing anesthesia or surgery.
Packed red blood cells (pRBCs) are produced by centrifugation and separation from whole blood. These units have a refrigerated shelf life of approximately 35–42 days, depending on the preservative used, compared to stored whole blood, which can be stored for up to 35 days. An advantage of pRBCs is that they avoid administration of unnecessary components and excess volume, thereby reducing the risk of complications, such as transfusion-associated circulatory overload, febrile non-hemolytic transfusion reactions, allergic reactions, and hemolytic reactions. The volume of pRBCs to be administered can be calculated using one of the following formulas: 1) desired PCV rise (%) × 1.5 × body weight (kg); or 2) [(desired PCV – patient PCV) ÷ donor unit PCV] × blood volume (mL/kg) × body weight (kg).
Platelet transfusions are indicated in patients with thrombocytopenia or thrombocytopathy accompanied by significant bleeding. Prophylactic administration is less straightforward, as there is currently no consensus on whether this strategy reduces bleeding compared to a therapeutic-only approach, or on what platelet count should trigger transfusion. It is generally accepted that platelet transfusion prior to an invasive procedure can improve hemostasis in thrombocytopenic or thrombocytopathic patients.
In patients with immune-mediated thrombocytopenia (ITP), platelet transfusions have been shown to increase platelet counts transiently but do not result in meaningful improvement in clinical bleeding or survival. At this time, the ACVIM consensus statement recommends that platelet transfusion be considered only in cases of severe or life-threatening hemorrhage rather than for routine use.
Currently available platelet products include fresh whole blood, cryopreserved platelet concentrate in dimethyl sulfoxide (DMSO), and lyophilized platelets. Stored whole blood was historically thought to lack viable platelets; however, a recent study by Edwards et al. demonstrated maintenance of clot strength for up to 21 days, suggesting it may be a reasonable option when more specific platelet products are unavailable. Whole blood is typically dosed at approximately 10 mL/kg (with modest increases in platelet count expected), while platelet concentrates are generally dosed at 1 unit per 10 kg.
The non-cellular portion of blood includes water, electrolytes, and organic compounds such as proteins. The primary indication for plasma transfusion is replacement of deficient hemostatic proteins, including clotting factors and fibrinogen. These deficiencies are most commonly seen in patients with liver failure, anticoagulant rodenticide toxicity, or inherited disorders, such as von Willebrand disease or hemophilia A.
Other indications for plasma transfusion, such as albumin replacement or provision of antiproteases for pancreatitis, remain controversial. To increase serum albumin concentration by 1 g/dL, approximately 45 mL/kg of plasma is required. This volume is often impractical and cost-prohibitive. However, due to limited availability of canine albumin and concerns regarding adverse reactions with human albumin, plasma is sometimes used for colloidal support. In some settings, plasma may be administered as a continuous rate infusion in place of crystalloid therapy to support hemodynamic stability while helping to maintain (rather than significantly increase) protein levels. Patients that may benefit from this approach include puppies with parvoviral enteritis, dogs with acute hemorrhagic diarrhea syndrome, and septic patients with increased vascular permeability.
Fresh frozen plasma is separated from whole blood within eight hours of collection and contains all coagulation proteins, although levels may vary between donors. After storage at −30°C for one year, there is a decrease in certain labile clotting factors (particularly factor VIII), and the product is relabeled as frozen plasma, which can be stored for up to five years while retaining activity of more stable factors. Fresh frozen plasma can also be processed into cryoprecipitate and cryo-poor plasma. Cryoprecipitate contains concentrated amounts of von Willebrand factor, factor VIII, factor XIII, fibrinogen, and fibronectin. A typical dose is 1 unit per 10–12 kg body weight for coagulopathies involving these components. The supernatant remaining after cryoprecipitate production (cryo-poor plasma) contains factors II, VII, IX, and X, as well as albumin, and can still be used for oncotic support and replacement therapy in conditions like anticoagulant rodenticide toxicity.
Both canine-specific albumin (CSA) and human serum albumin (HSA) have been used in dogs. Human albumin is approximately 79.3% structurally homologous to canine albumin, and its use in critically ill dogs has been shown to increase serum albumin concentration, colloid oncotic pressure, and blood pressure. However, there is a significant risk of both type I and type III hypersensitivity reactions with HSA administration, which makes CSA the preferred option when available. Type I reactions can occur within minutes to hours of exposure, whereas type III reactions typically develop one to three weeks later and may be associated with significant morbidity and mortality. Therefore, the benefits of HSA administration must be carefully weighed against these risks.
Albumin dosing is typically calculated using the following formula: 10 × (2.0 g/dL – patient albumin [g/dL]) × body weight (kg) × 0.3. Approximately 450 mg/kg of CSA is expected to increase serum albumin by 0.5 g/dL; however, product availability and cost often limit the ability to administer the full calculated dose.
Regardless of the product used, transfusions should ideally be initiated slowly and closely monitored. If no adverse clinical signs are observed within the first 20 to 30 minutes, the rate can be increased, with the full dose typically administered over three to four hours. However, in cases of acute blood loss — particularly in unstable patients — blood products may need to be administered more rapidly to achieve hemodynamic stability. If a patient develops new clinical signs during a transfusion, administration should be paused immediately, and the patient should be assessed and treated according to the Transfusion Reaction Consensus Statement guidelines published in 2021.
