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Medicine Year 1 - Semester 2 - Part 2 > Blood Groups and Blood Transfusion > Flashcards

Blood Groups and Blood Transfusion Flashcards

1
Q

What are red cell antigens ?

A

Antigens present of the surface of red blood cells. (found in the lipid layer, extracellular)

26 blood group systems

  • ABO and Rhesus systems are most important
  • Kell, Duffy etc. less likely to cause clinical conditions
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2
Q

Describe an antibody-antigen reaction

A

Antibody produced by B cells in response to non-self antigens presented to T cells by antigen presenting cells - monocytes, macrophages

IgG antibodies mainly after exposure to blood transfusions or foeto-maternal transmission.

Naturally occurring IgM antibodies present at/soon after birth against antigens that the individual lacks.

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3
Q

Describe the structure of an antibody

A

Fab region - antigen binding region

Fc region - fraction crystallisable region

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4
Q

State the typical structure of an IgM antibody

A

Pentamer

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5
Q

Feature of IgM antibodies

A

IgM antibodies are more dangerous than IgG antibodies in immune hemolysis.

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6
Q

Describe the action of IgM

A

IgM antibodies can agglutinate red cells

IgM activates compliment and the membrane attack complex rapidly destroys cells

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7
Q

Describe the action of IgG

A

IgG does not damage circulating red cells.

Fc receptors on splenic macrophages bind IgG-coated red cells, which may then be gradually destroyed.

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8
Q

Describe the ABO system

A

FUT1 and FUT2 genes (on chromosome 19) code for H substance

A and B genes (on chromosome 9) code for glucosyl transferases which add further sugar groups.

Naturally occurring anti-A and/or B IgM antibodies in individuals lacking these antigens

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9
Q

H substance

A

Sugar chain that projects out from the cell surface.

Virtually everyone has H substance

(chromosome 19)

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10
Q

Function of A / B genes

A

Transfer one more sugar group onto the pre-existing chain of sugars (H substance)

(chromosome 9)

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11
Q

Group O

A

Neither A or B antigens

They have naturally occurring anti-A and anti-B antibodies.

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12
Q

Describe the A / B antigens location

A

Transmembrane antigens
Stick out into the plasma

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13
Q

Group O
(What antibodies are present ?)

A

Anti-A
Anti-B
(in plasma)
46% UK

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14
Q

Group A
(What antibodies are present ?)

A

Anti-B
(in plasma)
42% UK

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15
Q

Group B
(What antibodies are present ?)

A

Anti-A
(in plasma)
9% UK

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16
Q

Group AB
(What antibodies are present ?)

A

No naturally occurring antibodies

3% UK

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17
Q

Describe ABO grouping on a glass tile

A

Positive reaction = clumping of cells

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18
Q

Blood products examples

A

Plasma reduced cells

Pooled platelet concentrate

Fresh frozen plasma / cryoprecipitate

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19
Q

How is blood grouping carried out ?

A

Using gel columns
ABO and Rh grouping in micro-titre gel tubes

Positive reaction = cells held high in gel after centrifugation

20
Q

If a person is blood group O, what ABO antibodies would his plasma contain ?

A

Anti-A and Anti-B

21
Q

A person who is group A will have what characteristics on their red cells and in their plasma ?

A

A antigens on cells

Anti-B in plasma

22
Q

Describe the Rhesus system

A

Antigens c C D e E

Coded for on chromosome 1 and inherited as a triplet : e.g. cDe

‘Rhesus negative’ implies D negative

No naturally occurring antibodies but can develop in response to pregnancy or transfusion.

23
Q

Rhesus negative

A

D negative

24
Q

Difference between ABO and Rhesus system

A

Rhesus system does not have a naturally occurring antibody against antigens we lack.

We only develop them in response to blood transfusion or pregnancy.

25
Q

What is haemolytic disease of the newborn ?

A

Foetal red cells carry antigens from the mother and the father (includes Rh antigens).

The baby carries an antigen (from the father) that the mother does not have.

Foetal red cells carrying antigens from the father, transferring to maternal circulation.

Mother recognises these as not her cells, and so can produce antibodies against these.

26
Q

Describe what happens in haemolytic disease of the newborn

A

Mother produces IgG antibodies in response to (e.g. D, c, E, Kell)

Antibodies cross the placenta causing anaemia, jaundice, brain damage or foetal death.

27
Q

Explain how haemolytic disease of the newborn can affect the second pregnancy

A

In the 1st pregnancy, the Rh- woman has conceived a Rh+ foetus

During labour, foetal red cells leak into the mother.

The foetal red cells survive long enough to elicit an IgG response.

The maternal anti-D antibodies cross the placenta in the 2nd pregnancy and attack foetal red cells.

28
Q

Describe prevention of Rh D reaction

A

Via immunisation

Anti-D prophylaxis offered to D negative mothers @ 28 weeks + delivery + after obstetric events.

29
Q

Function of Kleihauer test

A

Looks for foetal cells in maternal circulation.

Acid elution (washing out) of Hb - foetal Hb is more resistant - looks darker circles (as Hb is not washed out)

30
Q

Describe foetal monitoring

A

Foetus of mother with significant red cell antibodies can be monitored for anaemia :

  • flow in middle cerebral artery
  • ascites
  • liver and spleen size (getting larger)

Umbilical cord sampling for blood count /blood group and antibody level

31
Q

Treatment of Rh D immunisation

A

Foetal monitoring by ultrasound

Can receive intra-uterine transfusion

32
Q

Describe neonatal management

A

Clinical assessment

  • Blood count
  • Phototherapy to increase bilirubin conjugation
  • Top-up or exchange transfusion
33
Q

Coombes test

A

Looks for membrane-bound antibody

  • Allow antibodies to decline
  • Top-up or exchange transfusion
34
Q

Describe cross-matching blood

A

Donor blood is checked for ABO, Rh D and other antigens

Microbiology screening - HIV, Hep B

Recipients blood is checked for ABO and Rh D group. Plasma is screened for antibodies against a panel of red cell antigens.

The recipients plasma is mixed with donor red cells to check for agglutination.

35
Q

Why is the recipients plasma mixed with donor red cells ?

A

To check for agglutination

  • If there is a reaction the cells will stay at the top of the tube
36
Q

Typical uses plasma reduced cells

A

Haematological conditions causing under production of blood :

  • Trauma
  • GI bleeding
  • Childbirth
  • Peri-operative
37
Q

Typical uses for platelets

A

Marrow failure
Massive haemorrhage

38
Q

Typical uses for fresh frozen plasma

A

Liver failure
Massive haemorrhage

39
Q

Blood transfusion consent

A

Formal signed consent is NOT taken in the UK

Leaflet and discussion about:

  • Risks and benefits
  • Alternative options

… but emergency use is valid, even if patient cannot give consent

40
Q

Describe transfusion reactions

A

Acute haemolytic reactions (pre-existing antibodies) usually due to miss-matched blood

Delayed haemolytic reactions (new antibodies formed following transfusion)

Urticaria or anaphylaxis
(drugs or plasma proteins)

Febrile reactions
(HLA antibodies)

41
Q

Which transfusion reaction is most serious ?

A

ABO mismatch is MOST serious

  • Group A individual has less anti-B than a group O individual
42
Q

Management of acute transfusion reaction

A

Stop the transfusion

Assess the patient

Return the blood bag, FBC, biochem, blood cultures, 3x transfusion tubes to lab

IV fluids

Monitor urine output, renal function and coagulation

43
Q

Acute transfusion reaction timings

A

Most severe reactions are within minutes of starting

44
Q

What to do in the case of a urticarial reaction ?

A

Temporarily stop blood

Gove IV piriton

Review 30 minutes

Continue transfusion if settling

45
Q

Some symptoms of anaphylaxis

A

Runny nose
Respiratory symptoms
Hives, Itchiness
Heart symptoms

Swelling of tongue, lips etc.

46
Q

Human errors in transfusion

A

Failure to establish patient identity and/or label tube incorrectly when taking blood

Failure to perform bedside check of patient identity when administering blood

Lab errors - e.g. incorrect sample used or antibodies not working

Medicine Year 1 - Semester 2 - Part 2 (53 decks)

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