Transfusion medicine (Proceedings)

Choosing the Transfusion Type

Common transfusion types include fresh whole blood, stored whole blood, packed red blood cells, fresh frozen plasma, and frozen plasma. Other, less common transfusion products include cryoprecipitate, cryo-poor plasma, platelet-rich plasma, platelet concentrate, lyophilized albumin, and lyophilized platelets. Choosing a transfusion to administer will depend on the specific needs of the patient.

Fresh whole blood (FWB) is blood that is collected from a donor and transfused to a recipient within 8 hours. It contains red blood cells, platelets, plasma proteins, clotting factors, and immunoglobulins. Fresh whole blood becomes stored whole blood (WB) after 8 hours. Stored whole blood contains the same components as fresh whole blood, but the platelets will be inactive. Whole blood is stored at temperatures between 1 and 6°C for up to 35 days.

Packed red blood cells (pRBC) are made from whole blood that has been centrifuged at high speed, and most of the plasma component has been removed. The resultant RBC units have a PCV of approximately 80%. RBC's are stored between 1 and 6°C for 20 to 35 days. Indications for use of red blood cell containing products include blood loss anemia, hemolytic anemia, and nonregenerative anemias. The advantages of pRBCs over whole blood are the decreased risk of volume overload and reduced exposure to plasma antigens. Packed RBC transfusions are administered to increase blood oxygen capacity in a patient that does not require albumin, clotting factors, or platelets.

Fresh frozen plasma (FFP) is prepared from whole blood by centrifugation at high speed, and then freezing the plasma supernatant within 6 hours of collection. The FFP units contain all the coagulation proteins, albumin, and immunoglobulins present in the starting whole blood unit. Storage at temperatures below -20°C retains clotting factor activity for up to 1 year. Plasma stored for more than 1 year is referred to as frozen plasma. This product does not contain the labile factors but is a source of other plasma proteins and clotting factors. The indications for plasma transfusion include control of active bleeding or as a pre-operative prophylaxis for patients with hereditary and acquired factor deficiencies. Plasma is used in cases of hemorrhage caused by severe liver disease, vitamin K deficiency, and DIC. FFP or FP can be used in the short-term management of hypoproteinemia or hypoalbuminemia associated with several underlying disorders. The benefit of FFP in these disorders is transient.

Cryoprecipitate is prepared by slowly thawing FFP at a cold temperature, and then centrifuging the partially thawed material to sediment the heavy, cold-insoluble proteins. The resultant cryoprecipitate contains an approximately 50% yield of Factor VIII, von Willebrand Factor, fibrinogen, and fibronectin in a volume approximately 1/10th of plasma. It is stored at temperatures below -20°C for up to 1 year. Major advantages of cryoprecipitate include small volume and ease of administration. Cryoprecipitate is the component of choice for treating Hemophilia A (Factor VIII deficiency), von Willebrand disease, and fibrinogen deficiency or dysfunction.

Cryopoor plasma is the remaining component after the production of cryoprecipitate. It contains all the serine protease clotting factors, anticoagulant and fibrinolytic factors, albumin, and globulin of FFP. It is stored at temperatures below -20°C for a 1 year or longer. Cryopoor plasma can be used for treating hemophilia B, deficiencies of vitamin K dependent factors, hypoproteinemia, or hypoglobulinemia.

Platelet rich plasma (PRP) is prepared by centrifugation of whole blood within 6 hours of collection at low speed. Units prepared from single units of whole blood are expected to contain > 5 × 1010 platelets in approximately 50 to 75 ml of plasma. PRP is maintained at room temperature from the time of collection until transfusion in order to prevent platelet activation and aggregation. PRP can be stored for up to 5 days but is best if used within 48 hours. Platelet concentrate (PC) is generated by the centrifugation of PRP at higher speeds and pooling of several units or from plateletpheresis. Platelet concentrate units contain approximately 3 × 1011 platelets per unit and are available from Animal Blood Resources International, Stockbridge, MI in fresh or frozen forms. Platelet transfusions should only be considered for patients with severe, life-threatening thrombocytopenia or severe platelet dysfunction and active hemorrhage or pre-surgery. PRP and PC are rarely indicated for use in immune-mediated thrombocytopenias, as the half-life of the transfused platelets will be extremely short.

Albumin

Blood types

Blood type refers to the glycolipids and glycoproteins on the surface of a red blood cell that are species-specific and antigenic. Antigenicity refers to the likelihood the immune system will react and make antibodies against the foreign substance. Individuals lacking a particular red cell antigen may develop antibodies against that blood type. These antibodies are responsible for incompatibility reactions.

Canine blood types are referred to as Dog Erythrocyte Antigens (DEA). There are 7 internationally recognized canine blood groups classified under the DEA system. The DEA 1 system appears to have more than one type, but DEA 1.1 is the most antigenic and appears to be responsible for serious transfusion reactions. Approximately 50% of all dogs are positive for the DEA 1.1 antigen. Recently, a new antigen referred to as Dal antigen has been described. Dal is found to have no correlation to known DEA antigens. The frequency of its occurrence and the clinical significance of the anti-Dal antibody are still largely unknown.

Only one blood group system has been previously identified in the cat. Three blood types make up the AB blood group system: type A, type B, and type AB. The A allele is dominant over the B allele. Type A is much more prevalent, but there exists a higher incident of type B cats among certain breeds, including Devon Rex, British Shorthair, Exotic Shorthair, Turkish Van and Turkish Angora. Among domestic shorthair cats, higher percentages of type B cats can be seen in certain geographic regions relative to others. Recently, a new blood-group antigen and clinically relevant alloantibody distinct from the AB blood group system have been identified. This new antigen is referred to as Mik. It has been shown that in Mik-antigen negative cats, anti-Mik is a naturally occurring alloantibody similar to anti-A and anti-B. An acute hemolytic transfusion reaction has been associated with the Mik-antigen in a renal transplant recipient.

Transfusion Reactions

The clinician has to be aware that there is always a risk of transfusion reactions when blood products are administered. Immediate or acute transfusion reactions are those that occur minutes or hours after the onset of transfusion. Delayed transfusion reactions may become apparent days to years later.

Incompatibility Reactions

Immediate hemolytic transfusion reactions occur due to hemolysis of transfused red blood cells by preformed antibodies present in the recipient's plasma. These are the most dramatic and rapidly life-threatening transfusion reactions. Clinical signs may include fever, tachycardia or bradycardia, hypotension, dyspnea, cyanosis, salivation, lacrimation, urination, defecation, emesis, collapse, opisthotonus, and cardiac arrest. In cases where and acute hemolytic reaction is suspected, the transfusion should be immediately stopped. Treatment is aimed at treating hypotension and shock, renal failure, and DIC. Most acute reactions can be prevented by using DEA 1 negative canine blood donors and matched feline blood donors. Crossmatch is also recommended prior to transfusion.

No clinically significant preformed alloantibodies have been recognized in the dog prior to sensitization with cells bearing the foreign antigen. Sensitization would occur if blood positive for DEA 1.1 was transfused into a DEA 1.1 negative dog. Subsequent transfusions with DEA 1.1 positive blood to the DEA 1.1 negative dog could be much more deleterious and result in life-threatening hemolytic reactions.

Following a transfusion, alloantibodies also may develop against other known or unknown blood types; these alloantibodies may be responsible for incompatibility reactions with subsequent transfusions.

Cats do possess naturally occurring alloantibodies against the blood type antigen they are lacking. Type B cats have strong anti-A antibodies, and type A cats have weak anti-B alloantibodies. The A-B incompatibility can result in a potentially fatal acute hemolytic transfusion reaction.

Nonhemolytic febrile reactions can occur with 1-2 hours of transfusion without associated hemolysis. These reactions are thought to be due to the recipient antibodies against donor leukocyte antigens. Treatment consists of cessation of the transfusion and antipyretics if warranted.

Acute, systemic anaphylaxis and urticaria are also forms of an immediate immunologic response to blood transfusion. It is suspected that this occurs secondary to antibodies against soluble proteins in donor plasma. This is a very rare reaction. Antihistamines may be indicated, and the transfusion may be instituted if the reaction clears.

Non-immunologic, immediate reactions

These occur in veterinary medicine and may be due to sepsis, circulatory overload, citrate toxicity, and nonimmune-mediated hemolysis. Septic reactions may occur if there has been bacterial contamination of the blood product. Fever, shock, hemoglobinuria, DIC and renal failure may follow. Gastrointestinal symptoms may also occur.

Delayed transfusion reactions

This is an immune-mediated reaction that can occur within 3 days or several weeks following transfusion and results in a shortened red blood cell lifespan. The reactions are due to antibodies against red cell antigens. Patients may be asymptomatic or develop fever or icterus. Therapy is infrequently required.

Infection

Potentially serious infectious diseases can be transmitted by blood transfusion, producing a nonimmune-mediated form of delayed reaction. Screening tests on donors for blood borne viruses, protozoa, and rickettsia are essential to exclude these infections. There are no established standards for infectious disease screening in donor cats, however it is recommended to screen for FeLV, FIV, and Mycoplasma spp. The PCR test should be used for Mycoplasma, and it is recommended to regularly test cats that have a shelter origin, regular outdoor access or exposure to fleas.

Cross-matching and blood-typing

Species-specific antisera, or chemical reagents directed against either canine or feline red blood cell antigens, are used in in-vitro blood-typing methods. A positive result may be in the form of agglutinating or lysing red cells.

Due to the antigenicity of canine DEA 1.1, blood typing for this blood type is crucial for potential donors. If the blood type of the recipient is unknown, a DEA 1.1 negative donor is used. In-house blood typing systems are available in cards (RapidVet-H DMS Laboratories Inc, Flemington, NJ) and gel column agglutination test methods (DiaMed-ID, DiaMed, Cressier sur Morat, Switzerland). Typing for more comprehensive canine typing is performed through reference laboratories.

The strict definition of the "universal donor" blood type is the DEA 4 positive dog that is negative to all other DEA types. However, it is more difficult to find donors that match this criteria, and screening for these dogs can become more expensive. However, this criteria is most likely to minimize the likelihood of an acute hemolytic transfusion reaction, maximize the lifespan of the transfused blood, and make future crossmatch most likely to be compatible with the recipient. More commonly, the "universal" donor is considered to be the DEA 1.1 negative dog, as DEA 1.1 is the only DEA implicated clinically as a cause of acute transfusion reactions. This improves the potential donor pool and decreases the expense of typing donors, however the red blood cell lifespan may be shortened, and sensitization of the recipients to DEA not typed for in the donor can occur. This would lower the probability of a compatible crossmatch when additional transfusions are required.

Given the potentially fatal reaction that can result from a mismatched transfusion, all feline blood donors and recipients should be typed, and a crossmatch should be performed. In-house feline typing cards are available (MS Laboratories, Flemington NJ, and DiaMed-ID, DiaMed, Cressier sur Morat, Switzerland). Feline typing is also performed at veterinary reference laboratories.

Crossmatching is directed at identifying possible incompatibilities against any blood type. Crossmatching detects the presence of hemolysin or agglutinin antibodies in the serum of one individual directed against the red cell antigens of a second individual. The crossmatch reaction does not predict future compatibility or confirm blood type identity of a donor-recipient pair. The major crossmatch combines donor cells with recipient serum. The minor crossmatch combines recipient cells with donor serum. The crossmatch control combines recipient cells with recipient serum. Hemolysis or agglutination in the control precludes interpretation of reactivity in the major and minor crossmatch.

Transfusion Guidelines

Transfusion therapy carries an inherent risk of disease transmission and adverse reaction, and the specific need for transfusion should be carefully defined for each patient. Each component unit should be carefully inspected to confirm identity and integrity, and complete transfusion records should be maintained. Most transfusion reactions can be prevented by careful consideration of blood type compatibility and transfusion procedures.

Strict aseptic technique should be used when performing a transfusion. No medications or fluids should be added to blood products or administered in the same catheter during a transfusion. All components should be transfused using blood administration sets with filters in order to avoid transfusion of cellular or fibrin aggregates. All plasma components must be carefully thawed and warmed to 37°C before administration.

The administration rate should initially be slow (0.5-1 ml/min) for the first half hour and then gradually increased to a maximum of 4 to 6 ml/minute. The animal should be monitored closely for temperature elevations, increasing respiratory rate, urticaria, and vomiting throughout the transfusion. It is recommended to check the above parameters every 5 minutes during the first half hour then every 15 – 30 minutes thereafter. Transfusions should be finished within 4 hours to minimize the risk of bacterial overgrowth.

The dose depends on the individual needs of the patient, but general dose recommendations have been made. Fresh whole blood is administered at 12 to 20 ml/kg. Packed RBCs, PRP, and cryopoor plasma should generally be administered at a volume between 6 and 12 ml/kg. Plasma is usually dosed between 10 and 20 ml/kg. Cryoprecipitate is recommended at a volume of 1 unit/15kg.

Conclusion

Transfusion therapy requires careful attention to the proper component therapy for each individual patient, proper donor selection, proper storage and handling of transfusion products, thorough pre-transfusion screening, strict aseptic technique, and careful monitoring of the recipient during a transfusion. The clinician should be aware of the risk to benefit ratio of transfusion medicine and should have a clear understanding of the different transfusion components and their recommended uses.

References available upon request