Blood Groups
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Blood Groups. DIFFERENT BLOOD GROUPS. ABO system. The membrane of RBCs contain antigens of two types (A) and (B) Characters of these antigens are : - inherited according to Mendelian law - appear in fetal life and persist throughout life.

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Blood Groups

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Blood Groups


DIFFERENT BLOOD GROUPS


ABO system

The membrane of RBCs contain antigens of two types (A) and (B)

Characters of these antigens are :

- inherited according to Mendelian law

- appear in fetal life and persist throughout life.

- specific reaction with the corresponding antibodies

In the plasma there are antibodies against A and against B and they also are inherited.


According to the types of antigens and antibodies, the blood groups are classified into:


universal recipients

universal donors


Importance of blood groups

In disputed paternity (good negative test).

In the criminal practice.

(1) Medicolegal importance:

(2) Blood transfusion

The recipient’s plasma should not contain

antibodies against the donor’s red cells


Incompatible blood transfusion

  • The donor’s RBCs are agglutinated by recipient plasma

  • The donor’s serum are diluted by recipient blood so its antibodies are with less or no effect on the recipient RBCs


RHESUS MONKEYS


Rhesus factor (Rh-factor)

People are divided according to the presence or absence of Rh- antigen (agglutinogen) on RBCs membrane into:

Rh +ve (have D- antigen) = 85%

Rh –ve (without D- antigen) =15%.


Rh-antibodies

They differ from ABO antibodies in:

1- They are normally absent

but induced by blood transfusion of Rh positive blood to Rh-negative patient

or in pregnancy.


2- Rh-antibodies are IgG but ABO-antibodies are IgM .

- IgM has large molecules and can’t cross placenta

- IgG has small molecules and can cross placenta.


Importance of Rh-factor

A- Erythroblastosis fetalis

Rh +ve male + Rh –ve female

 Rh +ve fetus

Rh +ve fetal RBCs enter the circulation of the mother and sensitize her liver to produce anti- D antibodies (agglutinins).


- Antibodies (IgG) cross the placenta to the Rh +ve 2nd fetus

- The 2nd or 3rd fetus is born anaemic, jaundiced or born dead

- The 1st baby is also affected if the mother is sensitized by previous transfusion of Rh +ve blood.


Prevention:

1- Rh –ve female should never receive Rh +ve blood

2- Anti-D antibodies are given to the mother during 48 hours after each delivery to neutralize the D-antigen of fetal RBCs transmitted to her  prevent formation of liver antibodies

Treatment:

Gradual replacement of baby’s blood with Rh –ve group O (exchange blood transfusion).


B- Repeated blood transfusion:

If Rh –ve person is transfused with Rh +ve blood he will produce antibodies against Rh-factor

if this person retransfused with Rh + ve blood  agglutination


Determination of blood group:

1- By slide technique


2-By cross matching between recipient and donor blood

Group A + Group B = Clumping of RBCs

+


Blood Transfusion


Indications:

1) Decrease blood volume (haemorrhage more than 30%).

2) In severe anaemia (Hb is less than 7gm/dl).

3) Restore blood contents as platelets,packed RBCs or clotting factor as in purpura and hemophilia

4) Erythroblastosis fetalis by exchange transfusion.


Precautions

1) Blood is obtained from healthy donors

- Age =18-60 year

- Weight: more than 55 kgm

- Blood pressure within normal range

- Hb% is not less than 90% (13gm/dl).

- Haematocrit value at least 40%.

- Free from infectious diseases as AIDS, viral hepatitis


2) Blood used is stored at 4C not more than 21 days

3) Blood bag must contain, sodium citrate (anti-coagulant), citric acid (reduce pH) and dextrose (nutrient of RBCs) .

4) Blood groups are compatible by double cross matching test

5) The blood is warmed before transfusion to restore the Na-K pump


Complications of blood transfusion

A- Incompatibility whichleads to:

1. RBCs are agglutinated in clumps 

block small blood vessels  pain in chest and back

2. Agglutinated RBCs hemolyse and hemoglobin is liberated in plasma and Converted to bilirubin  post-transfusion jaundice and precipitated in renal tubules blocking it  renal failure .


B- Other complications

1-Transmission of diseases as AIDS & hepatitis B,C.

2- Excessive transfusion  heart failure.

3- Hyperkalemia  arrhythmia

4- Hypocalcemia  tetany

5- Allergic reactions


Changes occur in storedblood

1- Increase K+ ions in plasma (Na-K pump inhibited by cold) .

2- Decrease dextrose and changed to lactic acid.

3- Decrease Platelets number .

4- RBCs swell and become spherical.

5- Decrease clotting factors VII, VIII , IX

6- Decrease 2,3 DPG  less O2 supply to the patient  hypoxia.


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