Blood Groups

Inheritance of ABO

Blood group of a person depends upon the two genes inherited from each parent. •Gene Aand gene Bare dominant, gene Ois recessive.

Treatment for Erythroblastosis Fetalis

If mother is found to be Rh negative and fetus is Rh positive : •Anti D antibody should be administered to the mother at 28th and 34th weeks of gestation, as prophylactic measure. If Rh negative mother delivers Rh positive baby Anti D should be administered to the mother within 48 hours of delivery (this develops passive immunity and prevents the formation of Rh antibodies in mother's blood.) If the baby is born with erythroblastosis fetalis, the treatment is given by means of exchange transfusion

Cross-matching

Is always done before blood transfusion. It is done to find out whether the person's body will accept the donor's blood or not; is done by mixing the serum of the recipient and the RBCs of donor. Matching = Recipient's RBC + Test sera Cross-matching = Recipient's serum + Donor's RBC

Rh factor

Is an antigen(membrane proteins) present in RBC •This antigen was discovered by Landsteiner and Wiener •It was first discovered in Rhesus monkey and hence the name 'Rh factor'. •There are many Rh antigens but only the D antigen is more antigenic in human. The persons having D antigen are called 'Rh positive' without D antigen are 'Rh negative'. Rhesus negative occurs only with complete absence of D!!!! •Rhesus factor is an inherited dominant factor. •It may be homozygous Rhesus positive with DD or heterozygous Rhesus positive with Dd.

Rh Antibody (or anti-D antibody)

Not present naturally •Produced onlywhen Rh negative person receives Rh positive blood! •If antibodies are present in mother's blood, can be transferred to the fetus

Determination of ABO group

1.If agglutination occurs with antiserum A: The antiserum A contains α-antibody. The agglutination occurs if the RBC contains A antigen. So, the blood group is A. 2. If agglutination occurs with antiserum B: The antiserum B contains β-antibody. The agglutination occurs if the RBC contains B antigen. So, the blood group is B. 3. If agglutination occurs with both antiseraA and B: The RBC contains both A and B antigens to cause agglutination. And, the blood group is AB. 4. If agglutination does not occur either with antiserum A or antiserum B: The agglutination does not occur because RBC does not contain any antigen. The blood group is O.

ABO Agglutinins

ABO antibodies are found in plasma of individuals in whom respective antigens are absent. •Appear in 2nd week of neonatal life. •They are globulins that belong to IgM category (do not cross placenta). •They are naturally occurring antibodies as they are formed without prior exposure to the antigens

ABO system

Based on the presence or absence of antigen Aand antigen B, blood is divided into four groups: 1.'A' group 2.'B' group 3.'AB' group 4.'O' group. •Blood with antigen A and β-antibody belongs to'A' group. •Blood with antigen Band α-antibodybelongs to 'B' group. •If both the antigens are present, blood group is called 'AB' group,serum does not contain any antibody. •If both antigens are absent, the blood group is called 'O' group and both α and β antibodies are present in the serum

Blood typing

Is done on the basis of agglutination. •Agglutination means the collection of separate particles like RBCs into clumps or masses. •Agglutination occurs if an antigen is mixed with its corresponding antibody which is called isoagglutinin.

Blood Transfusion complications

Jaundice: Normally, hemoglobin released from destroyed RBC is degraded and bilirubin is formed from it. When the serum bilirubin level increases above 2 mg/dL, jaundice occurs Cardiac Shock: Hb released into the plasma ↑es the viscosity of blood. This ↑es the workload on the heart leading to heart failure Renal Shutdown: The toxic substances from hemolyzed cells cause constriction of blood vessels in kidney. The toxic substances along with free Hb are filtered through glomerular membrane and enter renal tubules. Because of poor rate of reabsorption from renal tubules, all these substances precipitate and obstruct the renal tubule. This suddenly stops the formation of urine (anuria).

ABO blood groups

Landsteiner found two antigens (agglutinogens) on the surface of RBCs and named them as A antigen and B antigen •two corresponding antibodies (agglutinins) in the plasma and named them anti-A(α-antibody) and anti-B(βantibody.) Landsteiner law states that: 1.If a particular agglutinogen (antigen) is present in the RBCs, corresponding agglutinin (antibody) must be absent in the serum. 2. If a particular agglutinogen is absent in the RBCs, the corresponding agglutinin must be present in the serum. •AB agglutinogens are highly antigenic!!!

Blood transfusion

Only compatible blood must be used. •'Donor' is the one who gives blood; •'Recipient' is the one who receives the blood While transfusing the blood: •antigen of the donor and the antibody of the recipient are considered!!!; •the antibody of the donor and antigen of the recipient are ignored mostly. •RBC of 'O' group has no antigen and so agglutination does not occur. So, 'O' group blood can be given to any bloodgroup persons and the people with this blood group arecalled 'universal donors'. •Plasma of AB group blood has no antibody. •This does not cause agglutination of RBC from any other group of blood. •People with AB group can receive blood from any blood group persons. •So, people with this blood group are called 'universal recipients'.

Blood transfusion therapy

Packed RBCs: ↑ Hband O2 carrying capacity Acute blood loss, severe anemia Platelets: ↑ Platelet count (↑ ≈ 5000/mm3/unit) Stop significant bleeding (in qualitative platelet defects, thrombocytopenia) Fresh frozen plasma: ↑ coagulation factor levels cirrhosis, immediate warfarin reversal Cryoprecipitate: Contains fibrinogen, factor VIII, factor XIII, vWF, fibronectin Coagulation factor deficiencies

Placental barrier

Usually placenta acts as barrier to fetal blood entering maternal circulation. •However, sometimes during pregnancy or birth, fetomaternal haemorrhage (FMH) can occur. •The woman's immune system reacts by producing anti-D antibodies that cause sensitization At the time of delivery, the Rh antigen from fetal blood may leak into mother's blood because of placental detachment →within a month after delivery, the mother develops Rh antibody in her blood

Rh incompatibility

When a Rh negative person receives Rh positive blood for the first time, he is not affected much, since the reactions do not occur immediately. •The Rh antibodies develop within one month. So, a delayed transfusion reaction occurs. •But, it is usually mild and does not affect the recipient. So, when this person receives Rh positive blood for the second time, the donor RBCs are agglutinated and severe transfusion reactions occur immediately !!!

Erythroblastosis fetalis

(Hemolytic disease of fetus and newborn) •Is characterized by abnormal hemolysis of RBCs (the presence of erythroblasts in blood). •Usually the first child escapes the complications of Rh incompatibility!!!. •This is because the Rh antigen cannot pass from fetal blood into the mother's blood through the placental barrier. •It is due to Rh incompatibility: •When a mother is Rh negative and fetus is Rh positive (the Rh factor being inherited from the father) To compensate the hemolysis of more and more number of RBCs, there is rapid production of RBCs, not only from bone marrow, but also from spleen and liver which leads to many large and immature cells in proerythroblastic stage being released into circulation

Transfusion reactions

Are the adverse reactions in the body, which occur due to transfusion error that involves transfusion of incompatible (mismatched) blood. •In mismatched transfusion, the transfusion reactions occur between donor's RBC and recipient's plasma. Causes: •The recipient's antibodies adhere to the donor RBCs, which are agglutinated and destroyed. •Large amount of free hemoglobin is liberated into plasma. This leads to transfusion reactions. If the donor's plasma contains agglutinins against recipient's RBC, agglutination does not occur because these antibodies are diluted in the recipient's blood !!!.