Unit 20 - Immunohematology Flashcards
What is the most common blood type group?
Type O
What is the least common group?
Type AB
What determines blood type?
The glycolipid antigens located on the surface of your red blood cells.
Terminal sugars confer the antigenic specificity (A, B, O)
Note: there are two alleles for this, and blood type can be co-expressed.
What is the H-antigen?
The core sugar chain of the red blood cell antigens. The sugars that confer antigenic specificity are added to its terminal end via glycosaltransferase.
What are isohemagglutinins?
The A or B antibodies in the blood plasma.
These are created to foreign antigens that are not the self antigens located on that person’s RBCs.
Person is exposed to these foreign antigens via the environment.
What class of antibody are A and B antibodies? Why is that important?
IgM! IgM is large and does NOT cross the placenta. Will not see a fetus as foreign.
A titer of these antibodies can help diagnose B-cell immunodeficiency.
What is the Bombay Genotype? What does it look like?
Bombay genotype: O_h. Can not make glycosaltransferase…therefore there is no core H-antigen.
Appears as type O (no A or B antigens on RBC because they can’t attach to the non-existent core H-antigen.)
How is type O given to types A, B, or AB?
Type O can be given to anyone (universal donor) AS LONG AS it is the red blood cells only.
If whole blood is given, the antibodies to A and B antigens that the type O donor has in their plasma would interact with the receiving patient.
The Ab would destroy the recipients RBC via complement.
Do human RBCs have MHC antigens?
No. There are no MHC presented antigens, but there are A and B antigens.
Do platelets have HLA?
Yes. Platelets carry HLA Class I. After multiple transfusions, this can cause alloimmunization problems.
HLA typing is expensive and hard.
Can A or B antigen vary in their expression?
Yes. One may be expressed weakly and make it difficult to type and match…may need to DNA type.
How is donated blood screened?
It is tested for antibodies to: syphilis hep B hep C HIV West Nile
Reverse typing makes sure the isohemagglutinins are correct for the initially determined red blood cell type.
What is cross match?
There are antibodies in the recipient’s plasma that can react with the antigens on the donor’s red blood cells…that are not A or B or Rh antigens.
“Does the recipient ‘see’ the donor cells?”
If so, complement mediated hemolysis, inflammation, and free hemoglobin deposited in the kidneys…
How might cross match be tested and avoided?
Use an agglutination test.
What is the antiglobulin test?
Used to test donor’s blood before banking. Agglutination = positive.
There are two:
- Direct Coombs Test –> Check if the donor has Ab to his own RBCs (bad! could be hemolytic anemia). Use a lab Ab to the human Ig and check for agglutination.
- Indirect Coombs Test –> Test for problems if the recipient has had multiple transfusions. Check if the donor’s plasma has Ab to the Ag in the recipient’s plasma.
Note: one more step = INDIRECT
