Transfusion Medicine Simplified

Transfusion medicine is a hot topic in Emergency and Critical Care and one that DVM STAT consultants often receive questions about.  

Fast Facts about Blood Typing and Crossmatching

Canine Blood Types: 

• There are at least 13 blood types in dogs as well as the Dal antigen.  The most important canine blood type is dog erythrocyte antigen 1.1 as DEA 1.1 incompatibility results in severe hemolysis. 

• Dogs don’t have preexisting alloantibodies and pregnancy does not result in antigen sensitization.  In short, a dog can receive a first-ever transfusion without a crossmatch.  

• All dogs should be typed and ideally, type specific blood products should be utilized (ie. 1.1 positive dog receives 1.1 positive blood).  In practice, many hospitals only stock DEA 1.1 negative blood since both DEA 1.1 positive and DEA 1.1 negative dogs can receive it safely. There is often a national shortage in DEA 1.1 negative blood products and stocking both positive and negative units conserves resources.  

• It takes 4-5 days for antibodies to develop after a transfusion so for EVERY subsequent transfusion (>5 days after a transfusion), a major and minor crossmatch is necessary to prevent a potentially fatal transfusion reaction. 

Feline Blood Types: 

• Cats have either type A, type B or less commonly type AB blood. Some cats also lack the Mik antigen, a minor RBC antigen, and can develop hemolytic transfusion reactions even with blood type (A or B) specific blood.   

• Cats DO have preexisting alloantibodies and importantly ALL CATS REQUIRE BLOOD TYPING BEFORE TRANSFUSION. 

• While there is controversy about how important a crossmatch is before feline transfusion, a major crossmatch, at minimum, is a good standard of practice to ensure that there is a lower probability of severe transfusion reaction. 

• It takes 3-4 days for antibodies to develop in cats, a bit quicker than in dogs, so for EVERY transfusion (>3-4 days after a transfusion), a major and minor crossmatch is necessary to prevent a potentially fatal transfusion reaction. 

Crossmatching: 

• Crossmatches can be completed immediately in-hospital using gel-based crossmatch kits or can be submitted to a reference lab or animal blood bank if there is not an emergent need.  

• Patients with autoagglutination can not be crossmatched in-hospital until a RBC wash is completed to “remove” the RBC Ag:AB complexes and therefore eliminate the agglutination. 

• Crossmatch Simplified:

  • Major Crossmatch: Donor RBC and patient plasma - “major component of transfusion = donor RBC”

  • Minor Crossmatch: Donor plasma and patient RBC - “minor component of transfusion = plasma antibodies in the unit”

Transfusion Decisions Should be Made on a Case-by-Case Basis.  

Transfusion Trigger:

There is no HCT or PCV number that serves as a “transfusion trigger.”  Physical examination remains the single best diagnostic tool.  Clinical evidence of decreased oxygen delivery to the tissues include tachycardia, tachypnea, weakness and hyperlactatemia. These signs of hypoxia will be evident with even mild-moderate anemia in acutely anemic patients, whereas a PCV of 10-15% may be tolerated in patients with chronic anemia. 

Anemia Duration Matters  

Acute Anemia: 

Patients with acute anemia don’t have any ability to compensate for the immediate drop in oxygen carrying capacity (Hb).  Acute patients present with tachycardia, tachypnea, weakness, hyperlactatemia and sometimes signs of myocardial hypoxemia (arrhythmias).  In peracute blood loss anemia, these clinical signs of hypoxemia may be present even before the PCV drops significantly; remember that the TS decreases well before the PCV drops in patients with acute blood loss anemia (link to February newsletter). 

Chronic Anemia: 

We’ve all seen patients with chronic anemia like the geriatric cat who is seemingly asymptomatic with a HCT of 11%. It's often a shock when we receive those CBC results - severe anemia may not have even been on the differential list!   There are many physiological adaptations that allow chronically anemic patients to tolerate severe anemia. These include a left shift of the oxy-hemoglobin dissociation curve allowing easier oxygen offloading to the tissues, increased 2-3 diphosphoglycerate and increased cardiac output secondary to decreased viscosity, among others.    

In patients with chronic anemia, red blood cell transfusions often need to be considered in patients undergoing anesthesia or surgery.  Less commonly, patients with chronic anemia begin to show clinical signs of generalized weakness, lethargy, inappetance, tachycardia, and tachypnea and on a case-by-case basis, transfusion may be an appropriate treatment step. 

Rapid detection of anemia and need for transfusion means earlier hemodynamic stabilization and improved medical outcomes.  

DVM STAT Criticalists are available to you 24/7 to consult on hemodynamic stabilization, management of anemia and coagulopathy and transfusion medicine.  

We also provide ongoing Blood Bank Development Consultations and support to hospitals and referral centers to guide the development of their new self-sustaining blood bank programs.