Blood groups -The outer layer of RBCs

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Blood groups

-The outer layer of RBCs membrane contain certain antigens which are chemically glycoproteins and called agglutinogens. -According to the presence of these antigens , human blood can be classified into many groups. -Most of these antigens are weak and are mainly of importance in genetic studies.

ABO system -This system includes 2 types of antigens A and B agglutinogens. -According to the presence of A and B antigens there are 4 groups of human blood : 1 - Group A (about 41% ) : when only type A antigen is present. 2 - Group B (about 9 % ) : when only type B antigen is present. 3 - Group AB (about 3 % ): when both types A and B antigens are present. 4 - Group O (about 47 % ): when both types A and B antigens are absent.

Plasma contain certain antibodies against the red cells agglutinogens called agglutinins which are 2 types : - Anti-A (or Alpha) agglutinins. - Anti-B ( or Beta ) agglutinins.

Rh system (Rh factor) -This is system of agglutinogens normally present in the red cells of Rhesus monkey (hence the name Rh) -There are 6 varieties known as(dominant C , D and E) (antigens and recessive c , d and e ) antigens. -These antigens were also found in the human red cells. -Antigen D has the strongest antigenic effect So : gen is present → Rh +ve. If D antigen is absent → Rh -ve.

Significances of blood grouping: 1 - Blood transfusion. 2 -Marriage ( Rh incompatibility). 3 -Disputed paternity. 4 - Detection of criminals(Medico-legal).

Determination of ABO system -Mix one drop of blood with 1 ml of isotonic saline in a test tube. -Put 2 separate drops of the diluted blood on a glass slide. -Add one drop of anti-A serum (blue coloured) to one blood drop and one drop of anti-B (yellow coloured) to the other drop. -Mix the blood with anti-A and anti-B sera gently using the blunt end of two separate pins.

-After 2 minutes examine for agglutination : a- If agglutination occurs with anti-A serum only , the blood group is type A. b- If agglutination occurs with anti-B serum only , the blood group is type B. c- If agglutination occurs with both anti-A and anti-B sera , the blood group is type AB. d- If no agglutination occurs with either anti-A or anti-B , the blood group is type O.

Determination of Rh group -Put 2 drops of diluted blood on a glass slide. -Add one drop of anti-D serum to the blood and mix gently with the blunt end of a pin. -Examine for agglutination : f agglutination occurs , the blood group is Rh +ve. -If no agglutination occurs , the blood group is Rh –ve.

Indications of Blood transfusion - After hemorrhage. - Severe anemia. - Hemophilia. - Purpura. - Leucopenia. - Severe infections. - Chronic leukemia.

Precautions before blood trasfusion 1 - Trasfused blood should be compatible with that of recipient. 2 - The Hb content of transfused blood must be not less than 90 %. 3 - The transfused blood should be free from diseases. 4 - The transfused blood must be fresh and not frozen. 5 - Cross matching test should be done.

Complications of incompatible blood trasfusion Incompatible blood transfusion leads to agglutinations of the donor‘s red cells followed by their hemolysis and results in the following : 1 - Severe pain elsewhere in the body. 2 - Hemolytic jaundice. 3 - Chest pain. 4 - Dyspnea. 5 - Chills and fever. 6 - Hypotension.

Complications of blood transfusion. 1 - Incompatibility due to mismatched blood groups. 2 - Allergic reactions. 3 - Bacterial infections. 4 - Transmission of diseases 5 - Massive blood transfusion leads to circulatory overload.

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