Haem - Blood transfusion

Question 1

What are the 4 blood groups and what antibodies do they have respectively?

Answer 1

A - anti-B
B - anti-A
AB - none
O - anti-A/anti-B

Question 2

What characteristics are there of blood antibodies?

Answer 2

• Present from birth
• IgM class
• Capable of fully activating complement - fatal haemolysis if mixed transfusion

Question 3

How are A/B antigen formed?

Answer 3

Sugar residue on common glycoprotein & fucose stem (H antigen)
A - galnuc
B - gal
O - N/A

Question 4

How are antigens determined?

Answer 4

Gene code for:
A - enzyme to add N-acetyl galactosamine
B - enzyme to add galactose

Question 5

What is the genetic pattern of ABO genes?

Answer 5

AB co-dominant

O recessive

Question 6

How is a blood transfusion deemed incompatible?

Answer 6

If there is agglutination of Abs and anti-Abs

Question 7

Why is O- group blood available to everyone?

Answer 7

It has no antigens

Question 8

What and how are components of the blood split?

Answer 8

Centrifuge (top - plasma, middle - platelets, bottom - RBC) and squeeze into satellite bags

Question 9

What can plasma function be further split into?

Answer 9

• FFP (fresh frozen plasma)
• Cryoprecipitate
• Plasma for fractionation - Albumin//factorVIII: XI immunoglobulins, anti-D etc.

Question 10

Where is blood collected from donor?

Answer 10

Collected into sterile bags containing anti-coagulant

Question 11

Why is it not efficient to use whole blood to transfuse patients?

Answer 11

Patients only need some components, can risk excess fluid overload eg anaemia

• less waste of valuable resource

Question 12

What is one unit of blood?

Answer 12

Whole blood derived from single donation

Question 13

What is the Rh system?

Answer 13

Antigen D - where Rh D negative means no D antigen & vice versa

Question 14

What are the genotypes of blood groups?

Answer 14

A: AA/AO
B: BB/BO
AB: AB
O: OO

Question 15

What are the genotypes of +ve & -ve RhD?

Answer 15

+ve: Dd/DD

-ve: dd

Question 16

Why must sensitisation (exposure to D antigen) be avoided?

Answer 16

To avoid creating anti-D in RhD negative people

Question 17

How can sensitisation (exposure to D antigen) be avoided?

Answer 17

• Transfuse blood with same RhD

- Use O- blood

Question 18

How can sensitisation happen and what implications does it bring?

Answer 18

Transfusion
-Future +ve transfusion can react to cause “delayed haemolytic transfusion reaction”
Pregnancy (mother -/foetus+)
- 2nd pregnancy - Mother IgG anti-D Abs cross placenta to cause haemolysis of foetal RBC - “Haemolytic disease of the newborn”

Question 19

How does the severity of “Haemolytic disease of the newborn” HDN determine the baby’s fate?

Answer 19

• Not severe: Baby survives with high bilirubin levels –> brain damage/death
• Severe: Hydrops fetalis –> death

Question 20

Why can mother anti-D Abs cross placenta?

Answer 20

It is of IgG class, only they can cross

Question 21

What other RBC antigens are there?

Answer 21

Dozens more (Eg Cc Ee Kell Duffy Kidd) but only 8% form antibody - those need to use corresponding negative blood or risk delayed haemolytic reaction

Question 22

How to we test patient before transfusion?

Answer 22

1. Compatibility test - antibody screen on patient plasma (incubated with 2/3 different fully “screening” RBC) to exclude clinically significant immune antibodies
   - if -ve, any blood given
   - if +ve, identify antibody using panel
   - -> select donor
2. Cross match - patient serum mixed with chosen RBD donor
   - -> should not react

Question 23

What blood donors are excluded?

Answer 23

• Risk to oneself (cardiovascular/neurological disease)

- Risk to others (infections, drugs, blood-borne diseases [early stage not yet detectable])

Question 24

What are the two tests done on donor blood?

Answer 24

1. Grouping and screening - test to ensure no strong clinically significant RBC abs are in donor plasma other than ABO groups
2. Infection testing
   - but cannot pick up all infections

Question 25

Why can we not reply on infection testing donor blood?

Answer 25

Test for infections cannot pick up all infections, especially those that are not detectable in early stages

so only give to those who need it

Question 26

What is Prion disease?

Answer 26

Normally - Prion protein found in membrane of lymphocyte & platelet

Prions of variant Creutzfeldt-Jacob disease (CJD) found in lymphoreticular tissues
(4 cases by blood transfusion - test is not available)

Question 27

What are the infections tested on donor?

Answer 27

HIV
Hepatitis B,C,E
HTLV
Syphilis

Others:
CMV (cytomegalovirus)
T. Cruzii
Malaria