Blood Transfusions/Groups

Goals of transfusions

• replace only what is needed

• provide increased oxygen carrying capacity, restore blood volume, replace coag factors/proteins

Indications for blood transfusions

• rapid blood loss (PCV <20%)

• severe chronic non-regenerative anemia (PCV <15% dogs, <12% cats)

• life-threatening IMHA

• hypoproteinemia (albumin <1.5 g/dL)

• thrombocytopenia (<10×10^9/L)

• coag factor deficiency

Blood components

• packed RBC

• plasma (fresh or fresh frozen)

• platelet rich plasma (not very helpful in vet med)

• cryoprecipitate & cyropoor plasma (slowly thawed fresh frozen plasma)

• therapy by components allows for more efficient use of blood & longer shelf lives

Whole blood

• collected in anticoagulant

• used for hemorrhage or patients that need RBCs + coag factors

Packed RBCs

• whole blood centrifuged to PCV of 70-80% & diluted in saline

• used to prevent volume overload or when pt only needs RBCs (IMHA, non-regenerative anemia)

Ideal blood donor animals

• dog: 1-6yrs old, 55+ lbs, >40% PCV (50% sighthounds), DEA-1 negative (positive can donate to positive)

• cat: 1-6yrs old, 10+lbs, >35% PCV, type A for domestics, type B for some purebreds

• can donate 5-6 times/year, in good health & on preventative care, should not have had previous blood transfusions

Adverse reactions to blood transfusions

• immunologic: acute hemolytic, acute non-hemolytic, delayed hemolytic

• non-immunologic: acute, delayed

Acute hemolytic transfusion reactions

• due to RBC incompatibility, avoided by crossmatching prior to transfusion

• causes intravascular hemolysis in minutes-hours

• signs: fever, restlessness, salivation, tremors, vomiting, anuria, incontinence, tachycardia, convulsions, thromboembolism, AKI, shock, death

• treatment: stop transfusion, administer fluids + corticosteroids + antihistamines

Acute non-hemolytic transfusion reactions

• most common, occur from recipient antibodies vs donor plasma proteins, WBCs, or platelets, not always prevented by crossmatching

• signs: pruritus, fever, anaphylaxis

• treatment: stop transfusion, administer fluids + corticosteroids + antihistamines

Delayed immunologic transfusion reactions

• recipient develops antibodies vs donor RBC antigens in days-weeks post-transfusion

• causes hemolysis + shorter RBC lifespan

• signs: decreased PCV, increased bilirubin

Non-immunologic transfusion reactions

• may be acute or delayed

• include: hemolysis from improper blood collection/administration, circulatory overload, hypocalcemia (citrate intoxication), disease transmission, endotoxic shock

Blood group systems

• groups of genetically related antigens (glycolipids & glycoproteins on the RBC membrane)

• expression governed by gene sequences in RBC precursors

• compatibility necessary for safe transfusions

Naturally-occurring antibodies

• antibodies to blood group antigens not expressed on an individual’s RBCs despite no previous exposure to those antigens

• mechanism is unknown

• ex: all type B cats have clinically relevant levels of antibodies vs type A RBC antigens

Formation of anti-RBC antibodies

• can be induced by blood transfusions (within 4-7 days), exposure to certain infectious agents/drugs, NI, or idiopathic (IMHA)

Canine blood groups

• express DEA 1.1, 1.2 or neither (DEA-1 positive = 1.1 or 1.2 present)

  • ideal donors are DEA-1 negative

• most do not have clinically relevant levels of naturally-occurring antibodies

• distribution varies with breed & country

Feline blood groups

• one major system with 3 types: A, B, AB

• >95% DSH/DLH cats are type A (depending on geographic area)

• purebred cats are more often type B

Blood typing

• species specific typing reagents used to cause a visible reaction (agglutination, hemolysis, etc.)

Crossmatching (major vs minor)

• used to determine donor compatibility to prevent acute transfusion reactions since we rarely know patient blood type

  • does not prevent delayed transfusion reactions

• can be done in a microtiter plate, in a test tube, or on a glass slide; agglutination and/or hemolysis = incompatible donor

• major: donor cells + recipient serum

• minor: recipient cells + donor serum

Crossmatching in dogs

• most dogs with no previous transfusions can be given a transfusion without crossmatching (most dogs don’t have naturally-occurring antibodies)

• dogs with transfusion history must be crossmatched

Crossmatching in cats

• cats, especially purebreds, must be crossmatched for any transfusion (high prevalence of anti-A antibodies in type B cats)

Neonatal isoerythrolysis

• maternal-fetal incompatibility in horses or cats, mother is negative for an antigen expressed on the baby RBC

• mare exposed to foal RBC antigens from retro-placental hemorrhage during pregnancy or previous transfusion & makes antibodies vs foal (may take multiple pregancies)

• foal exposed to antibodies during colostrum ingestion, bind to foal RBCs & cause intra + extravascular hemolysis

Findings in NI

• weak & dyspneic foals within hours to days

• pallor/icterus

• regenerative anemia with increased serial MCV

• hemoglobinemia/uria

• bilirubinemia/uria

• Dx via agglutination test (foal blood + mare colostrum or serum)

Prevention & management of NI

• don’t breed mare w/history of NI foal w/same sire

• crossmatch sire RBCs w/mare serum prior to parturition, use different colostrum if hemolysis present

• minimize stress + reduce exercise, provide supportive care, transfuse foal with compatible RBCs such as from mare