Blood Groups Flashcards
Blood Types
erythrocyte membrane-bound molecules that can differ between animals + can be interpreted as antigenic epitopes by immune cells, prompting immune response(s)
Clinical Relevance of Blood Types
molecules can generate type II hypersensitivity response 🡒 an antibody-mediated immune reaction in RBC destruction in:
- animals with naturally occurring antibodies (alloantibodies)
- animals that have developed antibodies after previous exposure to foreign RBC antigen(s)
RBC Antigens + Antibodies
- erythrocyte membrane is a lipid bilayer that contains other mol. such as transporters
- blood types + factors based on specific molecules present in RBC membrane
- these structures act as antigenic epitopes + therefore commonly referred to as RBC antigens
Alloantibodies
naturally occuring antibodies against specific foreign RBC antigen, which are present from birth in certain species
cats + horses = main vet species
Transfusion Reaction
occurs when we introduce RBCs with antigens into a recipient animal’s vasculature in whcih antibodies directed at those are present
opsonization of RBC + removal by splenic macrophages = extravascular hemolysis
activation of complement MAC with subsequent RBC pore formation = intravascular hemolysis
Reaction may consist of 1 or mix of responses below:
1) agglutination
- d/t antibody binding to antigen on cell surface
- antibody 🡒 hemagglutinin
- leads to premature removal of transfused/neonate RBCs
- more common in small animals
2) hemolysis
- rupture of erythrocyte within vasculature
- antibody 🡒 hemolysin
- leads to acute intravascular hemolysis
- more common in large animals
outward signs = fever, pruritis, facial swelling, vomiting/diarrhea, pigmenturia, icterus/jaundice
Sensitization
occurs when animal is exposed to RBC antigens different than their own
- through pregnancy, parturition or transfusion/exposure to blood product
following exposure, immune system develops antibodies against foreign RBC surface antigen
re-exposure to to (now) incompatible blood antigen can elicit transfusion reaction
encounter this most commonly in dogs
Feline AB system
3 blood types 🡒 A, B, AB
frequency of blood types can vary based on geography
naturally occuring alloantibodies common
- present without receiving previous transfusion
Feline Type A
most common (>90% of cats)
most mixed breed cats in US
have naturally-occuring alloantibodies against B antigen
antibodies are weak hemagglutinins + hemysins
- leads to early removal of Type B transfused into Type A cat
- relatively mild transfusion reaction
Feline Type B
usually purebred cats but can occur in mixed breed cats
naturally-occuring alloantibodies against A antigen
causes SEVERE hemolysis of Type A when transfused into Type B cat
- antibodies are naturally present at high conc. in blood
- STRONG hemagglutinins + hemolysins
Feline Type AB
have both A + B antigens on RBC surface
bc both surface antigens present, no naturally-occuring antibodies
rare, <1% of cats
- high incidence in ragdolls
give type A blood if AB not available
Dog Erythrocyte Antigen (DEA) System
DEA1 is highly immunogenic + considered most important
~60% of US Dogs are DEA 1(+)
Neonatal Isoerythrolysis
destruction of neonate’s erythrocytes induced by antibodies indigested with dam’s colustrun
cats + horses of greatest concern
low incidence but may result in neonatal death
Neonatal Isoerythrolysis
Feline
occurs in Type A or AB kittens born to Type B queens
anti-A antibodies from queen transferred to kitten via colustrum
can happen with a 1st litter 🡒 d/t naturally-occuring anti-A antibodies
Neonatal Isoerythrolysis
Horses
Aa + Qa are strongly immunogenic + most important in NI
usually doesn’t occur in foal produced from 1st mating
- typically requires prior sensitization via previous pregnancy
Donkey Factor
RBC antigen found in donkeys + mules only
- horse alloantibodies to Donkey factor suspected
- therefore all mare pregnancies with mule foal are at risk for NI
- no prior pregnancy/sensitization necessary
Blood Typing Tests
commerically availbale tests
- cards, cartridges + gel columns
use antibodies against specific blood groups (antisera)
can be done in clinic
Large Animal + Exotics
Blood Typing
likely impractical to blood type individuals
safest to do crossmatch prior to transfusion
may be impossible in field
Crossmatching
diagnostic test that assesses for blood incompatibility between animals
- some animals with same blood type will still be incompatible
most commonly used to ID a compatible donor
- occ. animals with compatible crossmatch results will still develip transfusion reaction (unknown/other causes)
may be used to predict NI in horse/mule foals
- expose sire’s RBCs to dam’s serum
Major + minor crossmatches are seperate tests
Major Crossmatch
tests recipient’s serum against donor’s RBCs
attemps to simulate in vitro what’s happening in vivo with transfusion
- look for evidence that recipient has antibodies that recognize donor RBCs 🡒 agglutination +/or hemolysis
- want to avoid incompatibility bc massive lysis of transfused RBCs in patient is extremely dangerous
Minor Crossmatch
tests donor’s serum against recipient’s RBCs
looks for evidence that donor has antibodies that recognize recipient RBCs
- clinically 🡒 an incompatibility is considered much less dangerous
if using packed RBCs (little plasma) then a inor crossmatch is generally not necessary
Which test(s) to perform?
cross matching
If using whole blood for transfusion :
- both major + minor crossmatch recommended
if using packed RBCs for transfusion:
- only a major crossmatch recommended
- requires serum (or EDTA plasma) from recipient + aliquot of packed RBCs from donor
Crossmatching
Compatible v Incompatible
Compatible results 🡒 no damage to erythrocytes
Incompatible result:
1) agglutination of RBCs d/t antibody binding to antigen on cell surface
- multiple antibody binding sites results in cross-linking of erythrocytes
- RBC clumping referred to as agglutination
- antibody 🡒 hemagglutinin
2) hemolysis 🡒 lysis of RBCs
- rupture of erythrocyte within vasculatue (in vivo)
- antibody 🡒 hemolysin
Blood Volume + Sampling
blood volume as % of BW varies by species
typically:
- 2-3 mls from cats + dogs
- < 10 mls for production animals + horses
- ~ 100-500 uL from pocket pets, reptiles, birds, etc.
- typically extrapolate these guidelines to similar wildlife + zoo species
How much blood can I safely draw from my patient?
loss of 30% blood volume expected to result in hypovolemic shock
up to 20% total blood volume can be lost without complication in many animals
in healthy small mammals + birds, typically draw 10% or less of total BV
