Immunohematology Flashcards
What is immunohematology? What is its importance?
branch of hematology that studies antigen-antibody interactions as they relate to the pathogenesis and clinical manifestations of blood disorders
uses blood typing to identify possible risks of erythrocyte hemolysis during blood transfusions to find compatible blood donors
What determines blood groups?
species-specific inherited antigens present on the surface of RBCs
What are alloantibodies?
(isoantibodies) = naturally occurring antibodies against other blood types or foreign tissue present without prior exposure
Where do antibodies arise from?
“alien” antigens from transfusion, transplacentally, or trauma
What is neonatal isoerythrolysis (NI)?
hemolytic anemia that occurs in foals that inherit the sire’s blood group antigens (Aa, Qa) born to mares of a different blood types to the stallion
- dam will have antibodies to the stallion/offspring RBCs in the colostrum
- foal will be born healthy put undergo hypersensitivity after ingesting the colostrum
What 2 tests are performed during a transfusion? What is the point?
- blood typing
- crossmatching
classifies the animals blood type by determining with antigen(s) are present on the RBC membrane and if there are antibodies present in the serum
What is blood typing used to select? How does this happen?
permanent blood DONORS
uses an antiserum or a reagent to identify specific RBC antigens, causing a cross-reaction
What does crossmatching detect? How is this done?
if a recipient has antibodies in serum against a donor’s RBCs
patient serum is tested against a donor’s RBC or serum,
+ if a recipient’s antibodies attach to the RBC
What are the 2 types of antibodies to blood group antigens?
- naturally occurring (alloantigens)
- acquired after exposure to the blood group antigen
What are the 4 main causes of the development of anti-RBC antibodies? In what animal species does this naturally occur?
- transfusions
- cross-placental transfer during pregnancy (horse)
- vaccination with blood origin products
- autoimmune disease (IIMHA)
felines
What are the 8 major blood groups in dogs? Which ones are the most immunogenic?
- DEA-1.1*
- DEA-1.2*
- DEA-3
- DEA-4
- DEA-5
- DEA-6
- DEA-7
- DEA-8
What does it mean if a dog is DEA-1.1 or DEA-1.2 negative?
they have no naturally occurring antibodies
What is considered the universal donors and recipients in dogs?
DONOR - DEA-1.1 negative, DEA-4 positive
RECIPIENT - DEA1.1 positive
What dogs can receive blood from DEA1.1 negative donors? DEA1.1 positive donors?
What are 4 common signs of acute hemolytic transfusion reactions? What does this have the potential to do?
- severe intravascular hemolysis
- hemoglobinuria
- hyperbilirubinemia
- transfused RBCs only last <12h n vasculature making them useless
massive activation of immune and clotting systems leading to shock, renal failure, circulatory collapse, and death
What 6 breeds of dogs are likely to be universal donors? What blood type do they typically have?
- Greyhounds
- Boxers
- Irish Wolfhounds
- German Shepherds
- Dobermans
- Pit Bulls
DEA1.1 negative
What is the blood typing system like in cats?
AB system
- Type A (dominant)
- Type B
- Type AB
What species is at the highest risk of first-time transfusion reactions? Why?
cats - they have natural alloantibodies against other blood types
What is the most common blood type in cats in the USA? What species typically have this type? What are their antibody levels like?
A
DSH, DLH, non-pedigree cats
low levels of naturally occurring ant-B antibodies
What are the antibody levels in cats with type B blood like? What types of cats typically have this type?
high levels of anti-A antibodies
EXOTIC cats - British Short Hair, Abyssian, Himalayan, Cornish Rex, Devon Rex
What are the antibody levels in cats with type AB blood like?
no naturally occuring anti-A or anti-B antibodies (can receive any blood)
What kittens are in danger of neonatal isoerythrolysis? In what 2 breeds does this happen?
AB kittens born to a B queen and A/AB tom
- Devon Rex
- Birman cats
Feline blood groups:
A-B mismatches can cause fatal hemolytic reactions
What are the levels of pre-existing alloantibodies like in large animals? For the most part, blood typing and transfusions are impractical and uncommon. What is the exception?
the presence of alloantibodies is rare
horses
Single unmatched whole blood transfusions are well-tolerated in large animals. In what 2 situations should an animal be crossmatched?
- repeated transfusions
- plasma transfusions
How many blood groups are there in horses? Which 3 are the most important? Most immunogenic?
7 blood groups and 30 RBC antigen types
A, C, Q
Aa, Qa* —> anti-Aa and anti-Qa antibodies lead to neonatal isoerythrocytosis
When does equine neonatal isoerythrolysis typically develop in the foal? What kind of hypersensitivity is it?
newborn disease - first week of life
type II hypersensitivity causing hemolytic anemia
What is the pathogenesis of equine neonatal isoerythrlysis? When does this most commonly occur?
- mare starts to produce Ab against foal’s RBC inherited from the stallion
- Abs are transferred into the colostrum
mare and stallion with different blood types —> mare is sensitized by the first pregnancy and starts to affect the second foal of the same mating pair
How can a mare become exposed to blood from a fetus with different blood type to cause neonatal isoerythrolysis?
( MARE AND STALLION MUST HAVE DIFFERENT BLOOD TYPES - mares negative for RBC factors are also at higher risk)
- placentitis
- difficult parturition
- foreign blood factors from previous transfusion
What are the 5 clinical signs of foals affected by neonatal isoerythrolysis?
- lethargy, weakness
- icterus
- increased pulse rate and respiratory rate
- hemoglobinemia, hemoglobinuria
- severe hypoxia leading to convulsion, coma, and death
How can neonatal isoerythrolysis be avoided in mares and foals before pregnancy? After?
screen mares for blood type and antibodies for compatibility with the stallion
test colostrum and avoid allowing foal to feed if it has anti-blood type antibodies (use frozen or another mare)
Why are cows not commonly transfused?
over 80 RBC antigens yielding around 2 trillion blood types - impractical
- single unmatched whole blood transfusions are generally safe and well-tolerated
- crossmatch recommended for repeat transfusions
How does blood typing and crossmatching compare?
BLOOD TYPING identified the RBC antigens on the cell surface to identify blood groups - DOESN’T detect antibodies between patient and potential donor
CROSSMATCHING identified antibodies against RBC antigens
What are the 2 types of crossmatching? How are each done? What do the results mean?
- MAJOR: predicts if DONOR RBCs will be attacked by RECIPIENT antibodies (serum) - wash donor RBC in recipient serum
- MINOR: predicts if DONOR antibodies (serum) will attack RECIPIENT RBCs - wash recipient RBC in donor serum
- hemolysis/agglutination = incompatible
- no hemolysis/agglutination = compatible
Crossmatch interpretation:
How do cats compare with other animals with the need for crossmatching?
CATS - can naturally have alloantibodies against other blood types, so crossmatching is always required, even for the first transfusion
DOGS/HORSES - not common to have naturally occurring alloantibodies, so sensitization must occur before they develop antibodies - if it is 100% positive it is the animal’s first transfusion, a crossmatch is not necessary
When do animals typically require transfusions?
- acute anemia
- hypovolemia
- thrombocytopenia
- hypoproteinemia
What are the 5 characteristics of a good donor?
- blood-typed
- healthy with regular vaccines
- no RBC parasites, FeLV, FIV, or EIA
- never transfused
- free of most reactive antigens
What are the best characteristics of dog, cat, and horse donors?
DOG - DEA-1.1 and DEA-1.2 negative
CAT - type A (can be B in certain regions)
HORSES - young geldings or females that have never been transfused or pregnant and lack Aa/Qa antigens
What are the 2 types of blood transfusion reactions? What happens with each?
- IMMEDIATE (minutes to hours) - rapid intravascular hemolysis, hemoglobinemia, hemoglobinuria, fever, seizures
- DELAYED (7-10 days) - progressive anemia, icterus
What are 2 possible non-RBC-related reactions to improper blood transfusions?
- transmission of infectious organisms, like Mycoplasma and Babesia spp. (screen donors!)
- sensitized patients to subsequent transfusion reactions
In what animals is immune-mediated hemolytic anemia a possible consequence in improper transfusions? What kind of sensitivity is this?
dogs, occasionally cats
RBCs are destroyed by antibodies directed against them - Type II hypersensitivity
What 3 things are commonly seen in a peripheral blood smear in immune-mediated hemolytic anemia?
- autoagglutination
- regenerative anemia
- spherocytes
What are 3 major characteristics of acute immune-mediated transfusion reactions?
- severe intravascular hemolysis
- causes DIC, hypotension, shock, acute renal failure, and death
- induces a reaction from IgM and complement fixation (ghost cells)
In what animals are acute immune-mediated transfusion reactions? Uncommon?
CATS - if type B cat is given Type A or AB blood, since they have naturally occurring alloantibodies
DOGS/HORSES - 1st transfusion is usually safe, reactions are caused by the presence of acquired antibodies
What are 3 major characteristics of delayed immune-mediated transfusion reactions?
- mild extravascular hemolysis
- causes decreased PCV >24h and up to 2-3 weeks post-transfusion, hyperbilirubinemia, bilirubinemia, and a positive direct Coombs’ test
- induces a reaction from IgG and causes the formation of spherocytes
When is it common for delayed immune-mediated transfusion reactions to occur?
1st transfusion in dogs - incompatible blood, sensitization to other antigens other than DEA-1.1 and DEA-1.2
What are the 2 parts of the Coombs’ test? What do they detect?
- DIRECT ANTIGLOBULIN TEST (DAT) - detects anti-RBC antibodies or complement on the surface of RBCs
- INDIRECT ANIGLOBULIN TESt - detects anti-RNB antibodies in the serum of the patient using their serum against washed RBCs from sire, offspring, or possible donors
In what animals does the Coombs’ test have no diagnostic value?
non-anemic animals
What are the 6 steps to the procedure of the Coombs’ test for IMHA? What does a positive result mean?
- collect blood into an EDTA (purple top) tube
- wash erythrocytes
- suspend in buffered saline
- mix with species-specific Coombs’ reagent containint antiglobulins against IgG, IgM, and complement
- incubate at 37 degrees C for 30 mins
- centrifuge and check for agglutination/hemolysis
there is IgG, IgM, or C3 on the patient’s RBCs
(can have false negatives and positives!)
What are 6 possible causes of false positives not associated with IMHA in the Coombs’ test?
- post-transfusion
- cross-reactive antibodies in Coombs’ reagent
- bacterial or particulate contamination of Coombs’ reagent
- in vitro complement binding during storage
- infections (Babesia, Mycoplasma)
- neoplasia (histiocytic sarcoma)
What are 3 causes of negative reactions in animals with IMHA on the Coombs’ test? What is important to note about negative results?
- concentration of antibodies on RBCs is below sensitivity of the test
- previous treatment with steroids
- elution of weakly bound antibodies off the RBC during the washing step
negative results do not rule out IMHA
What is the most common non-hemolytic reaction to transfusions? What kind of reaction is this? What is the cause?
febrile and allergic reactions - Type I hypersensitivity
IgE-mediated antibodies against allergens in donor blood, like antibiotics, chemicals from blood preparation, or albumin
What are the 2 common signs of febrile and allergic transfusion reactions? What type of transfusion typically causes this?
- minor skin reactions, like pyoderma, edema, wheals, and pruritus
- in severe cases: hypotension, bronchiolar constriction, increased vascular permeability, and cardiopulmonary arrest
plasma transfusions, typically within 15mins to a few hours
What should be done if a febrile and allergic reaction is observed during a blood transfusion?
stop transfusion and administer antihistamines
