week 5: Blood typing and blood transfusion

Question 1

What is the most common blood grouping system?

How many RBC antigens have been described?

How can they be grouped?

What are the most important blood grouping systems?

Answer 1

ABO blood grouping system

more than 400 RBC group antigens have been described.

These can be grouped together in 35 antigen systems

ABO and Rh blood typing is the most important system

Question 2

What is Landstiner’s law?

Answer 2

Landsteiner’s law bascially says if you’ve got the antigen then you cannot have the antibody, and if you’ve got the antibody then you cannot have the antigen.

E.g. if an agglutinogen is present on RBC membrane - the corresponding agglutinin (plasma antibody) must be absent in the plasma.

If an agglutinogen is absent on a RBC membrane then the corresponding agglutinin (plasma antibody) must be present in the plasma.

Question 3

Describe the ABO blood typing system

1) the antigens present and RBC type
2) the antibodies present in the plasma

Answer 3

Group A - A antigen, with anti-b antibodies in the plasma, therefore RBC type A

Group B - B antigen, with A antibodies in the plasma, therefore RBC Type B

Group AB - both A and B antigens, therfore no antibodies in the plasma and RBC type AB

Group O - no antigens in the RBC, therefore both anti-A and anti-B antibodies in the plasma, red blood cell type O.

Question 4

What is the distribution of A and B antigens?

Answer 4

A and B antigens are present on almost all types of human cells, in all bodily fluids and are weakly expressed at birth - detectable by 5 weeks gestation.

Question 5

What are antigens?

How can their structure differ?

What is the determining factor of A or B group?

What do the A and B genes encode for?

Answer 5

Antigens are oligosaccharides added to cell membranes, formed of slightly different subunits

Galactose —> galnac + Fuc = A antigen

A determinig sugar = N acetyl galactosamine

Galactose –> Gal + fuc = B antigen

B determining sugar = d Galactose

The product of the A and B genes are enzymes which attach the specific sugar onto a carbohydrate chain.

Question 6

How are the ABO antibodies acquired?

Answer 6

ABO antibodies are naturally acquired in response to environmental stimuli, newborns develop antibodies after birth.

Any antibody found at birth is usually maternal.

The titre may decline in old age.

Question 7

What type of antibodies are those to A and B antigens?

What can these antigens activate and therefore cause?

What do they rarely cross?

Answer 7

A and B antibodies are mainly IgM.

W smaller quantities of IgG.

Activate complement at body temp - 37 - therefore capable of causing intravascular haemolysis.

They rarely cross the placenta.

Question 8

ABO genetics:

Where is the ABO locus?

How many alleles are present?

What are their inheritance patterns?

Answer 8

ABO locus is on chromosome 9

There are three gene alleles - A, B and O (does not code for an antigen).

A and B genes are co-dominant. If individual has 1 A and 1 B allele, they will be blood group AB.

O allele is recessive and produces no antigenic product.

Question 9

Describe ABO inheritance

Answer 9

A and B alleles are codominant

O allele is recessive.

E.g. Type AO and Type BO having a child:

25% of being: AB, AO, BO, OO

Question 10

What are the frequencies of the ABO groupings in the UK?

Answer 10

Group O - 45%

A - 43%

B - 9%

AB -3%

Therefore 97% of the population has anti-A, antiB or anti-A and antiB in their plasma.

Question 11

How can the ABO blood typing change in different populations?

Answer 11

In SE asians or indians, B grouping is the most common

O is most common in native american and australian aborigines.

Half of africans have O, then more common to have A, then B then AB.

Question 12

What is the 2nd most important blood group system?

How many blood group antigens does this system include?

What are the most important antigens to know?

What is positive and negative in this grouping?

Answer 12

Rh system is the 2nd most important blood group system after ABO

Consists of 50 defined blood group antigens

D, C, c, E and e are the most important.

Rh +ve and Rh -ve refers to the D antigens only.

Question 13

Which chromosome is the Rh genes found on?

Answer 13

Rh genes are encoded on chromosome 1 .

The D antigen can be absent, but close proximity to the C and E antigens.

Question 14

What is the Rh D antigen?

Where is it found in the body?

What are the antibodies to them?

How do antibodies to this antigen occur?

can antibodies cross the placenta?

Answer 14

It is a polypeptide or protein antigen

only found on RBCs

the antibodies to them are only IgG

do not occur naturally, they are highly immunogenic - i.e If there is no D antigen, there will be no anti-D antibodies, so if the person is exposed to Rh antigen they will produce antibodies. If an individual is Rh+ve they will have no anti-D antibodies, and not produce any.

Antibodies can cross the placenta and cause haemolytic disease of the foetus and neonate.

Question 15

Why does the Rh system not fit with Landstiners law?

Answer 15

Rh +ve – Have D antigen but no D antibodies (Fits with the law)

If you are Rh -ve you also have no antibodies, but will produce antibodies if you are exposed to the antigen (does not fit with landstiners law)

Question 16

Frequencies of Rh antigens?

Answer 16

Rh D +ve - 85% (more common to have the D antigen than not)

Rh D -ve - 15%

Question 17

Combining the blood groupings:

What different blood types can you get?

Answer 17

Group A, and either Rh D positive (A + ) or Rh D negative (A-) (more common to be positive again, 36% vs 6.5%

Group B again + or - (less common overall, 7.6 vs 1.35%)

Group AB + or - (2.55% and 0.6%) (v uncommon)

Group O + or - (38% and 6.75%)

Group O (no A or B antigen) and rhesus negative - Group O negative - universal donor!

Question 18

Why is type O negative the universal donor?

Why can plasma not be given?

Answer 18

The blood CELLS will not cause an immune reaction, as they lack A, B and Rh antigens.

However the PLASMA cannot be given to others as it has many antibodies to it, both antiA and antiB antigens (probably not Rh antibody unless they have been exposed to it).

Question 19

What is the most important test pre blood transfusion?

Answer 19

ABO grouping is the single most important serological test performed on pretransfusion samples.

NHS NEVER event –> transfusion or transplantation of ABO incompatible blood components or organs

Question 20

What is required pre - transfusion

Answer 20

Step 1 - all patients requiring a blood transfusion or who are matched in expectation of a transfusion must be consented.

Consent should be taken by dr or nurse with the knowledge to answer any questions patients have of their tx.

Question 21

What are reasons for blood sample rejections?

How much tolderance is there for sample and transfusion request forms?

Answer 21

Not labelled fully, wrong blood in tube and labelled incorrectly.

There is ZERO tolerance with sample transfusion request forms

Question 22

What is the sample requirement pre transfusion?

Answer 22

Samples must be from 2 distinct phlebotomy episodes NOT 2 samples taken and labelled at the same time.

Latest BCSH guideline recommendation, and high incidence of wrong blood in tube.

1st sample can be a historical sample, 2nd sample which meets the sample validity timelines (is a recent sample).

Question 23

What is cross matching?

What two types of checks are there?

What is forward group ABO check?

Answer 23

Cross matching - is testing a patients blood type.

There are forward and reverse group checks.

Forward group ABO check –> patient Red cells mixed with known antiA or Anti B commerical antibodies.

If you mix blood from blood type A with antibody A you should get a haemolytic reaction, antibodies recognise the antigen, precipitation of cells. When mixed with Anti B there is no haemolysis.

Again in blood type B, haemolytic reaction when mixed with anti-B antibodies but not with anti A

In blood type AB, reaction when mixed with both.

Blood type O reaction with neither.

Question 24

Describe forward group Anti D testing?

Answer 24

Commerical antiD also available, mix patients blood with antiD antibodies.

If D antigen present you will get haemolysis in the tube. If no D antigen present then no haemolysis.

Question 25

What is reverse group ABO checking?

Answer 25

Take a sample of the plasma from the patient (so taking their antibodies) and mix it with known group A or known group B cells.

If you have Anti-A antibodies, haemolytic response with group A, not with group b

If patient has antibodies to group B, then response with B cells and not with A

If type AB no antibodies in plasma, therefore no response with the cells

If type O both anti A and B antibodies, reaction with both A and B cells.

Question 26

What is antibody screening?

Answer 26

Where patient plasma is mixed with more commerical RBCs of known phenotype, the pattern of reaction determines if an antibody is present in the patient.

E.g. Anti C, anti c, E/ e, K, k etc

Question 27

What is cross matching?

Answer 27

Blood group is ascertained –> by forward and reverse checks, A, B AB, or O, Rh positive or negative.

The patients plasma is then mixed with the RBC’s from the unit to be transfused, to check for agglutination.

This is the final check pre transfusion.

Question 28

When can blood be transfused directly without cross matching?

Answer 28

Called Electronic issue:

Patient has a historical control - previous group and save

the group is the same on both occasions

the patient is antibody negative

and has always been antibody negative.

If these criteria are filled then blood can be issued directly WITHOUT cross matching.

Question 29

What are the blood components available?

Answer 29

1) Plasma –> can be then fractionated to get plasma proteins, fresh frozen plasma (for clotting factors), and cryoprecipitate (fibrinogen).
2) Red cells
3) Platelets

Question 30

What is a haemolytic transfusion reaction?

Answer 30

Serious complication that can occur after a blood transfusion where there is a reaction between the transfused RBCs and the individuals immune system. When RBCs are destroyed the process is called haemolysis.

Question 31

What is haemolytic disease of the fetus and neonate? HDFN

Answer 31

• Mother developing anti Rh D antibodies if the fetus is positive for Rh D but she is Rh D negative.
• Mother being Rh D negative, therefore had no antibodies before, but the fetus is positive.
• During delivery Rh antigens enter the mothers circulation through breaks in the placenta, the mother is now exposed and begins to make anti D antibodies.
• First child is fine as the mother isn’t exposed to the Rh antigen until at birth. 2nd pregnancy is the problem –> where mother now has Anti -D antibodies and will attack a fetus with Rh +ve/D antigen.
• These antibodies can cross into the placenta and destroy fetal RBC’s.