Additional information about blood groups and transfusion:

(1) Glycoprotein molecule that contains sialic acid is known to be attached to the lipid and project from the surface as rod like structures. Thus red cell antigens may be glycolipids or glycoproteins.

(2) It has been suggested that the weak A and B antigen reactions in neonatal red cells are due to lack of the substrate on the red cells.

(3) The antigens of Rh, K, FY, JK, MNs, Di, Do and Se system as well as coa and Lua appear to be fully developed at birth.

ADVERTISEMENTS:

(4) Several red cell antigens like A, Al, B, H, Rh, MNs, P, Lu, K, Le, Fy, Jk and I system have been demonstrated on erythroblasts.

(5) Occasionally the expected iso agglutinins cannot be demonstrated in serum samples, especially if the serum is collected from an elderly patient.

(6) In conditions such as hypo or agamma globulinemia and leukemia the iso agglutinins may be absent.

(7) Although large number of subgroups is identified they may occasionally generate transfusion problems. Since the antigens are so weak they were not recognized and the red cells are mistyped as ‘O group’. If this happens in the case of donor’s blood group identification, it may lead to delayed transfusion reactions when large quantities of RBC’s were transfused.

ADVERTISEMENTS:

(8) In an obstetrical patient anti A is unimportant as it does not cause hemolytic disease of the newborn.

(9) Unusual Inheritance of the ABO genes: In extremely rare conditions, parent with A group can have a child with ‘AB group’ or an AB parent can have ‘O group’ child.

The families in which this has occurred have been thoroughly studied to rule out non paternity or non maternity. In these cases it is believed that the AB individual inherits both A and B genes on a single chromosomes from one parent and “O gene” from the other parent. In one family A and B were shown to have been transmitted together through four generations.

Exception to the rules of inheritance provides geneticists with material for speculation about the complexity of genes.

ADVERTISEMENTS:

(10) There are two kinds of H antigens. The more common anti H is a cold agglutinin (that reacts below room temperature). This antibody reacts more strongly with cells of group O, A2 and Al B cells. Because H antigen of Al and A/B seems to be well hidden, hence anti H is occasionally found in the serum of Al and A1B people. High tittered anti H may react at room temperature.

(11) H-gene constitutes to the expression of the A and B genes. H antigen found in greatest concentration in O group persons. The gene H is very common and most of the people are homozygous for H gene.

12) Inheritance of H is independent of ABO, but ABH antigens are all formed from the basic material. The basic material of H has a protein or lipid back bone to which sugars are attached. Addition of one more sugars to the chain creates a new antigen. The type of sugar and the position in which it is attached determine specificity of the antigen. The H, A and B genes each control the attachment of a different sugar. H gene acts first and attaches a sugar (fructose) to the basic material. The resultant molecule is recognizable as antigen H and is capable of reacting with anti H antibody.

13) Although the antigen I, i and the corresponding antibodies are not part of the ABO system, they seem to be related to it. The nature of the relationship is still obscure. Anti I react with the red cells of almost all the adults. Since they are cold agglutinins they rarely react above 300 C but react at room temperature 22-250C. They bind compliment to donor cells in room temperature.

ADVERTISEMENTS:

14) Not all cases of erythroblastosis fetalis /haemolytic disease of the fetus and new born could be explained by the presence of anti Rh in the maternal serum. Even in the absence of anti Rh antibodies some babies are born with haemolytic disease. This is due to the presence of antibodies. The antibodies are referred as “incomplete antibodies” by Race, “blocking antibodies” by Weiner. Another antibody that gives reaction similar to Rh but not identical to anti D is found when the search for better methods to identify anti Rh antigen is attempted.

15) The Rh antigens have definite molecular configurations that are repeated in many places on the red cell surface. There may be as many as 30 000D sites on each red cell.

16) D antigen is clinically the most important antigen of the Rh system because it is the most immunogenic antigen.

17) It is not possible to prevent foetal cells from reaching the mother but the formation of anti D can be suppressed by proper treatment immediately post partum.

ADVERTISEMENTS:

18) A blood type is classified as rare when more than 200 donors have to be screened to find one compatible donor with blood of that type. Existence of other blood groups does not have much importance in blood transfusion but they may cause difficulties during cross matching for blood transfusion. MN system, Duffy system, Kell system, Lewis system, p system, Luthern system, Kidd system, Diego etc are some of the other blood groups noticed in humans.

19) Anti A, anti B, are capable of fixing complement but the antibodies other than ABO system cause extra vascular haemolysis and usually produce milder signs and symptoms such as fever, anemia and jaundice.

20) Primary immune response to Rhesus antigen is weak. Low titer of antibodies may be found after 6-8 weeks of delivery. In many cases primary sensitization may not lead to detectable antibody response but during second and subsequent pregnancies with Rh+ foetus detectable levels of antibodies appear due to second immune response. The antibody most frequently responsible for the disease is anti D that is of IgG type immunoglobulin. It crosses placenta, coats D positive cells of foetus which are then destroyed by spleen.

20) Sensitization to the D antigen can be prevented by administration of Rh immunoglobulin to mother at 28 weeks gestation and again within 72 hours of delivery of Rh+ baby as well as after spontaneous or induced abortion and after amniocentesis. WHO has recommended following doses of ant Rh antibody.

ADVERTISEMENTS:

(1) Abortion less than 12 weeks – 050pg.

(2) Termination of pregnancy 12 weeks – 200-300 pg.

(3) Mismatched Rh blood transfusion- 25 pg/ml of red cells.