Chapter 6: Blood Groups Flashcards
Blood groups
Genetically determined antigens present on the membranes of red cells, ABO group, and rhesus systems.
How can antigens be detected?
By reactions with corresponding antibodies in plasma.
What type of antigens are found in the cell membrane of RBC’s?
A antigen, B antigen, both, or none.
What type of antibodies does the plasma contain?
Anti-A, anti-B, both, or none.
The 4 groups of people are divided based on?
The presence or absence of Antigen A and B on the membranes of RBC’s.
Agglutination
The reaction between antigens on RBC’s and corresponding antibodies in plasma results in agglutination of RBC’s, so antigens are called agglutinogens and antibodies are agglutinins.
Antibodies
Agglutinins
Antigens
Agglutinogens
Blood group name corresponds to?
Phenotype
Blood group A
Genotype: AA or AO
Agglutinogens red cell antigen: A
Agglutinins plasma antibodies: anti-B
Frequency: 40%
Blood group B
Genotype: BB or BO
Agglutinogens red cell antigen: B
Agglutinins plasma antibodies: anti-A
Frequency: 10%
Blood group AB
Universal Recipient
Genotype: AB
Agglutinogens red cell antigen: AB
Frequency: 5%
Blood group O
Universal Donor
Genotype: OO
Agglutinogens red cell antigen: O
Agglutinins plasma antibodies: anti-A and anti-B
Frequency:45%
When is determination of ABO groups important?
During blood transfusion.
Normally the donor’s red cells agglutinate with the corresponding antibodies of the recipient plasma. Why does the reverse rarely occur?
Due to dilution of the donor’s agglutinins in the large volume of the recipient’s blood.
What is important to do before blood transfusion?
It is important to do a cross matching test by adding the blood of the donor to the serum of recipient.
How is ABO blood group used medico-legally?
It is used medico-legally to exclude that a person is the father of a child, but it cannot prove the paternity since many people have the same blood group.
RH blood type: D factor
An antigen present on the membrane of the RBC’s of 85% of the population who are said to be RH-positive. It was first discovered in Rhesus monkey.
RH-negative
The remaining 15% of the population have no RH agglutinogen on their RBC’s so they are RH-negative. Neither RH-positive nor RH-negative people have anti RH-antibodies (anti-D antibodies) in their plasma.
When are RH-antibodies formed in the plasma of a RH-negative person?
They are formed when the antibodies are transfused with RH-positive blood and the person in this case is sensitized to RH-factor. If the person receives RH-blood again, agglutination and hemolysis of the RBC’s will result.
Can a RH-positive person form anti-D antibodies?
An RH-positive person never forms anti-D antibodies whether he receives Rh-positive or Rh-negative blood.
Erythroblastosis fetalis
(Rhesus hemolytic disease of newly born)
When an Rh-positive male marries a Rh-negative female, the fetus will be Rh-positive.
During delivery, a large number of Rh-positive fetal red cells enter the circulation of the mother and anti-D agglutinins of the immunoglobulins G type (igG) are formed in the blood of the mother who is now sensitized to the D-antigen.
What happens when an Rh-negative sensitized mother gets pregnant again?
If she gets pregnant again with a RH positive fetus, the antibodies (igG) in her blood cross the placenta to the fetus leading to agglutination and hemolysis of fetal RBC’s.
Usually the first baby escapes the damage but the next babies are affected.
What are symptoms of an affected baby?
At birth, the affected baby is severely anemic and jaundiced due to the excessive formation of bilirubin. The blood brain barrier of the fetus is not well developed so the bilirubin reaches the brain causing damage, a condition called kernicterus. In more severe conditions, the baby is born dead.
What is kernicterus?
The blood brain barrier of the fetus is not well developed so the bilirubin reaches the brain causing damage, a condition called kernicterus.
When can the first baby be affected?
If the Rh-negative mother is already sensitized by previous transfusion with Rh-positive blood.
Is there any fetal complication regarding ABO system?
No! Because the ABO antibodies cannot cross the placenta being of type M.
How to prevent erythroblastosis fetalis?
- Rh-negative female should never receive Rh-positive blood.
- When a Rh-negative female delivers a Rh-positive baby, anti-D antibodies are given to her immediately after delivery to neutralize the D-antigen of the Rh-positive fetal red cells that entered her blood, thus preventing sensitization of the mother.
Importance of Rh factors
Erythroblastosis fetalis and repeated blood transfusions.
Repeated blood transfusions
If a Rh-negative is transferred with Rh positive blood, he will produce agglutinins against Rh factor. If after sometime, this person is transfused again with Rh-positive blood, agglutination occurs.
Blood transfusion indications
- To restore whole blood hemorrhage
- To restore one deficient element such as RBC’s, WBC’s, Plasma proteins, platelets, and clotting factors.
- Erythroblastosis fetalis
Precautions before blood transfusion
- Blood should be matching and cross matching test should be done. An Rh-negative person is transfused with an Rh-negative blood.
- The blood must be free from contamination and disease.
- The transfused blood must be fresh, not stored for more than 21 days at 4 degrees Celsius with high Hb%.
Effects of incompatible blood transfusion
Agglutination of the donor’s RBC’s by the antibodies of recipient, then hemolysis which leads to:
1. Blockage of blood capillaries.
2. Hazards of intravascular haemolysis.
Blockage of blood capillaries
Blockage of blood capillaries occurs by the clumped RBC’s leading to:
1. Backache
2. Joint pain
3. Anginal pain if coronary vessel is occluded.
Hazards of intravascular haemolysis
- Shock
- Hyperkalemia
- Hemolytic jaundice
- Blockage of renal tubules
Shock
Due to release of bests in and other vasodilators resulting in drop of ABP.
Hyperkalemia
K+ is released from RBC’s resulting in cardiac arrhythmia.
Hemolytic jaundice
Bilirubin is produced from hemolysed RBC’s leading to yellow coloration of the skin and mucous membrane (jaundiced).
Blockage of renal tubules
Hemoglobin is filtered by renal glomeruli forming acid haematin that blocks the renal tubules, which may lead to renal failure.