Blood Groups

Question 1

Blood Types

Answer 1

erythrocyte membrane-bound molecules that can differ between animals + can be interpreted as antigenic epitopes by immune cells, prompting immune response(s)

Question 2

Clinical Relevance of Blood Types

Answer 2

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)

Question 3

RBC Antigens + Antibodies

Answer 3

• 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

Question 4

Alloantibodies

Answer 4

naturally occuring antibodies against specific foreign RBC antigen, which are present from birth in certain species

cats + horses = main vet species

Question 5

Transfusion Reaction

Answer 5

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

Question 6

Sensitization

Answer 6

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

Question 7

Feline AB system

Answer 7

3 blood types 🡒 A, B, AB

frequency of blood types can vary based on geography

naturally occuring alloantibodies common
- present without receiving previous transfusion

Question 8

Feline Type A

Answer 8

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

Question 9

Feline Type B

Answer 9

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

Question 10

Feline Type AB

Answer 10

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

Question 11

Dog Erythrocyte Antigen (DEA) System

Answer 11

DEA1 is highly immunogenic + considered most important

~60% of US Dogs are DEA 1(+)

Question 12

Neonatal Isoerythrolysis

Answer 12

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

Question 13

Neonatal Isoerythrolysis

Feline

Answer 13

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

Question 14

Neonatal Isoerythrolysis

Horses

Answer 14

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

Question 15

Donkey Factor

Answer 15

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

Question 16

Blood Typing Tests

Answer 16

commerically availbale tests
- cards, cartridges + gel columns

use antibodies against specific blood groups (antisera)

can be done in clinic

Question 17

Large Animal + Exotics
Blood Typing

Answer 17

likely impractical to blood type individuals

safest to do crossmatch prior to transfusion

may be impossible in field

Question 18

Crossmatching

Answer 18

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

Question 19

Major Crossmatch

Answer 19

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

Question 20

Minor Crossmatch

Answer 20

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

Question 21

Which test(s) to perform?

cross matching

Answer 21

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

Question 22

Crossmatching

Compatible v Incompatible

Answer 22

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

Question 23

Blood Volume + Sampling

Answer 23

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

Question 24

How much blood can I safely draw from my patient?

Answer 24

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

Question 25

Safe Volume for Sample Collection

Answer 25

easier to estimate that 10% of BW is blood volume (in all patients) + we can collect 10% if that amount

this is 1% of body weight (use 0.8% for reptiles)

this will often overestimate blood volume, but will underestimate BV that can be safely removed

draw minimum vol needed with very small +/or ill animals

follow guidelines of supervising clinicians