Immunohematology

Question 1

For persons of the A, B, AB and O blood groups, give the following data: most and least common groups; red cell antigens; specificities of the ABO antibodies in their plasma; safe donors to that type; safe recipients of blood from that type; possible genotypes.

Answer 1

In USA...     White       Black
    A               42            27
    B                9             21
   AB               3             4
    O               46           48
In other words...
White: O=A > B > AB
Black: O > A=B > AB

AB is always most rare. In whites, A and O dominate. In blacks, O dominates, A and B are almost equal

Question 2

Name the antibody class of most ABO isohemagglutinins

Answer 2

IgM - duh, it’s a carbohydrate!

Question 3

Explain the ABO antigen situation in a person of Bombay blood type, and the consequences of a transfusion of non-Bombay blood into such a patient.

Answer 3

Think of O, A, and B all having the same core 4 sugars in a row. That 4th sugar is capped on top of the other 3. Once you have that 4th, a transferase can then add a 5th sugar onto the side (A or B), unless you’re O in which case your transferase sucks and doesn’t work =\ People with Bombay lack that 4th capping sugar transferase, so there’s is only 3 sugars long (whaaaaaaat). So, even if a Bombay person has a gene for an A or B transferase, it won’t work. They can ONLY receive Bombay blood. Even regular O blood would cause in immune response

Question 4

Define the crossmatch, and explain why it is important. Explain how red cells are destroyed following a mismatched transfusion, and why this may be devastating to the recipient.

Answer 4

Crossmatch determines if there are antibodies in the recipient’s plasma which can react with antigens on this donor’s RBCs.

Basically:

1. Donor cells are suspended in saline
2. Add a drop of the recipient’s plasma
3. If there’s agglutination = there are lots of high-avidity antibodies in the serum (probably IgM). These are most dangerous because of their potent complement-activating ability.

This would cause generalized complement-mediated hemolysis and active-complement-mediated inflammation, and free hemoglobin deposited in the kidneys leading to acute renal failure.

Question 5

Compare and contrast the techniques of the direct and indirect antiglobulin tests and the questions they are designed to answer.

Answer 5

Direct:

1. Take pt RBC, wash them, and then add antibody against human IgG (Coombs)
2. If they had some human IgG sticking to their surface, this “antiglobulin” could cross-link it, and the cells would agglutinate.

Indirect:
1. Take normal RBCs, ADD pt plasma, rinse the cells, and THEN add anti globulin.

DAT tells you if there was Ab placed on RBCs in vivo. Indirect tells you if there was Ab in the plasma (good for HDN since Ab won’t be on mother’s cells but will be in plasma)

Question 6

Define heterophile antibody, and identify a common disease in which one type is increased enough to be useful diagnostically.

Answer 6

Cross-reactive Abs that are good for you. Example:
Patient gets mono and makes Ab to the virus. These Abs also bind/agglutinate sheep RBCs, so now we can use that as a test!

Question 7

In Hemolytic Disease of the Newborn(HDN), explain:

a. The consequences of severe hemolysis in the newborn.
b. The way in which the mother becomes sensitized.
c. The class of antibody to Rh(D) the mother makes.
d. The consequences of sensitization to subsequent fetuses.
e. The role of Rh-immune globulin.

Answer 7

a. Mother’s Abs cross the placenta and destroy the fetus’ RBCs. The fetus will be born jaundiced - bad b/c high levels of bilirubin (a breakdown product of hemoglobin) can cross the BBB and damage the basal ganglia, resulting in cerebral palsy or, if there is very severe damage, fetal death.
b. In the last trimester, and especially at the time of delivery, some RBCs from the baby enter the mother’s circulation.
c. IgG, duh - it crosses the placenta
d. Each subsequent pregnancy with an Rh(D)+ fetus boosts her response.
e. RhoGAM: Abs opsonize the fetal RBCs and they are destroyed before they get a chance to immunize the mother. She is not made tolerant, just not immunized

Question 8

Explain the situation in which ABO hemolytic disease of the newborn can occur.

Answer 8

Some mothers “naturally” have IgG anti-A or IgG anti-B antibodies. Perhaps sensitized from a previous pregnancy