ABO System

Question 1

Landsteiner’s Rule

Answer 1

In the ABO system when an antigen is present on the RBCs, the corresponding antibody is absent from the serum, and conversely, when the antigen is absent from the RBCs, the corresponding antibody is present.

Question 2

ABO Clinical significance

Answer 2

• The first blood group system to be discovered remains by far the most significant for transfusion practice.- ABO compatibility between donor and patient is the essential foundation on which all pretransfusion rests.

Question 3

Forward (Direct/Cell) Grouping

Answer 3

Testing unknown cells (patient or donor cells) to determine what ABO antigens are present is called forward grouping - also known as direct or cell grouping.

Question 4

Reverse(Indirect/Serum) Typing

Answer 4

Testing donor or patient serum against A and B cells to determine ABO group is called reverse or serum grouping. The reagent in this case are cells known to have the A or B antigen – you’re looking for the presence of ABO blood group antibody(ies) in the patient or donor. Remember, if a person lacks an antigen in forward grouping, they are expected to have the corresponding antibody.

Question 5

Mendelian Inheritance

Answer 5

In 1908 it was suggested that ABO groups were an inherited characteristic. Inheritance was first described in 1924 by Bernstein.

1. AllelesIt is postulated that three allelic genes, A, B and O, are operative at a single genetic locus on chromosome #9.
2. DominanceThe A and B genes are codominant and both are dominant to the O gene - which is recessive, or more precisely, an amorph (a gene which does not express itself phenotypically).

Question 6

Cis-AB

Answer 6

Cis-AB gene probably arose due to the unequal crossing over within the ABO locus. The individual that is genetically AB/O has less than the usual amount of A & B antigens on his cells. The cis-AB gene is confirmed by doing family studies. It is usually first noticed because the mating of an AB x O should not produce children who are AB or O. The gene is rare – not seen often.

Question 7

The basic precursor substance of all blood group antigens consist of three different sugars in a chain:

Answer 7

1) galactose
2) glucose amine
3) galactosamine

Question 8

ABO antigens found in plasma or on RBCs have precursor substance that is attached to a lipid,

Answer 8

called glycolipid in plasma or glycosphingolipid on RBC.

Question 9

ABO antigens found in secretions have precursor substance attached to proteins

Answer 9

glycoproteins.

Question 10

In blood bank we are concerned with antigens found on

Answer 10

the RBC, plasma and in secretions such as saliva.

Question 11

The terminal galactose on the precursor substance is attached to the N-acetylglucosamine in a beta 1→4 linkage in

Answer 11

type 2 precursor substance

Question 12

The terminal galactose on the precursor substance is attached to the N-acetylglucosamine in a beta 1→3 linkage in t

Answer 12

type 1 precursor substance

Question 13

The glycolipid chain on the RBC membrane is always

Answer 13

Type II