principles of blood transfusions

Question 1

how do you determine blood groups?

Answer 1

• red cells have antigens on their surface
• human plasma may contain antibodies to these antigens
• these can cause reactions: sometimes fatal
• this is the fundamental problem in blood transfusion

Question 2

how do ABO antibodies occur?

Answer 2

they occur naturally due to cross reactivity with gut bacterial antigens

Question 3

what are ABO antibodies?

Answer 3

they are IgM (pentameric) antibodies able to fix complement and cause red cell lysis

Question 4

what happens if you transfuse ABO incompatible blood?

Answer 4

causes intravascular lysis

Question 5

what happens if you give a life-threatening transfusion?

Answer 5

• shock, hypotension, tachycardia
• renal failure, loin pain, haemoglobinuria
• disseminated intravascular coagulation
• death

Question 6

what does it mean if you are blood group A?

Answer 6

you have A antigens on the surface of your red blood cells and B antibodies in your blood plasma.

Question 7

what does it mean if you are blood group B?

Answer 7

you have B antigens on the surface of your red blood cells and A antibodies in your blood plasma

Question 8

what does it mean if you are blood group AB?

Answer 8

you have both A and B antigens on the surface of your red blood cells and no A or B antibodies at all in your blood plasma.

Question 9

what does it mean if you are blood group O?

Answer 9

you have neither A or B antigens on the surface of your red blood cells but you have both A and B antibodies in your blood plasma.

Question 10

what does the lab do when you send a blood sample to them?

Answer 10

1) test the ABO group of the red cells

2) screen the plasma for ‘atypical antibodies’

Question 11

what are atypical antibodies?

Answer 11

• these arise due to sensitisation with foreign red cell antigens caused either by previous blood transfusion or by pregnancy
• atypical antibodies can cause blood transfusion reactions if the patient is transfused with incompatible blood in the future

Question 12

what is another name for the Coombs test?

Answer 12

anti-globulin test

Question 13

what is the anti-globulin test?

Answer 13

• uses anti-immunoglobulin antibody to agglutinate red cells

Question 14

what are the 2 types of anti-immunoglobulin?

Answer 14

• direct (DAT)

- indirect (IAT)

Question 15

what does direct (DAT) tell us?

Answer 15

• tells us if red cells are coated with antibody
• it is positive after a transfusion reaction and in HDN
• it s positive in autoimmune haemolytic anaemia

Question 16

what is indirect (IAT) used for?

Answer 16

• used in the lab for testing blood group antigens

- it can tell us if a patient is positive for Rhesus and other blood groups

Question 17

what happens if you are rhesus positive?

Answer 17

cannot develop antibodies

Question 18

what percentage of people are rhesus negative?

Answer 18

15%

Question 19

what happens if you are rhesus negative?

Answer 19

you can develop antibodies if they are transfused with Rh positive blood or are pregnant with a Rh positive baby - this is known as Rhesus sensitisation

Question 20

what antibody is generated during rhesus sensistisaiton?

Answer 20

IgG

Question 21

what is rhesus D sensitisation?

Answer 21

• persons who develop Rh antibodies cannot be given Rh positive blood
• if a mother who is Rh negative is pregnant with an Rh positive foetus, she may produce antibodies that can cross the placenta and harm the baby
• this is known as haemolytic disease of the newborn

Question 22

what are the symptoms of haemolytic disease of the newborn?

Answer 22

• anaemia
• jaundice
• kernicterus (brain damage)

Question 23

how do you prevent haemolytic disease of the newborn?

Answer 23

• pregnant women have the ABO+ Rh blood group check at 12 weeks
• Rh negative women receive anti-D antibody via injection at 28 and 34 weeks to prevent sensitisation
• baby tested at birth and if Rh positive, mother receives further anti-D until Kleihauer test (foetal cells) become negative
• if already sensitised then the foetus requires monitoring via trans-cranial Doppler scan and may require intra-uterine transfusions if signs of anaemia

Question 24

what is in a bag of donated blood?

Answer 24

• red cells
• buffy coat (white cells, platelets)
• plasma (albumin, gamma globulins, coagulation factors)
• water, electrolytes, additives

Question 25

what does a junior doctor need to know about blood transfusion?

Answer 25

• when to give a blood transfusion
• what type of transfusion to give
• how to request blood transfusion
• how to monitor a blood transfusion
• what are the problems and complications

Question 26

when do you give a blood transfusion?

Answer 26

• severe acute blood loss (severe trauma, massive GI blood loss, obstetric blood loss)
• elective surgery associated with significant blood loss
• medical transfusions (cancer, chemotherapy, renal failure)
• anaemia (only for symptomatic anaemia or if refractory to hematinic replacement, bone marrow failure, haemoglobinopathy)

Question 27

what are the different types of transfusions?

Answer 27

• blood components (red cells, platelets, fresh frozen plasma, cryoprecipitate/fibrinogen)
• plasma derivatives (pooled products) - immunoglobulin, coagulation factors, albumin
• cell salvage (rarely done during operations)
• autologous transfusion (very rarely done)

Question 28

what do you do during pre-transfusion testing?

Answer 28

• informed consent
• record reason for transfusion in notes
• sampler: ask patient their name and check ID on wristband
• make sure the patient gets the ‘right blood at the right time’
• most errors are caused by failure to follow procedures

Question 29

what information do you need to request for a blood transfusion?

Answer 29

• ID (surname, name, DOB< hospital number)
• blood group
• previous transfusions
• reason for request
• type of blood product and amount
• special requests
• when and where
• doctor

Question 30

what information do you need to put on the sample?

Answer 30

• ID
• signature of phlebotomist
• date
• do not use addressograph labels
• NEVER PRE-LABEL SAMPLE

Question 31

what do you do for compatibility testing in the lab?

Answer 31

• establish ABO and Rh group
• check for atypical antibodies in patient serum
• select donor blood
• compatibility testing between donor cells and patient serum
• issue blood with appropriate labels

Question 32

what is the availability of blood O negative?

Answer 32

• emergency blood

- immediate (5 mins)

Question 33

what is the availability of blood group that is the same as the patient?

Answer 33

10-15 minutes

Question 34

what is the availability of fully screened and cross-matched blood?

Answer 34

around 45 minutes

Question 35

what are the possible reactions of blood transfusions?

Answer 35

• major ABO incompatibilities (acute renal failure, disseminated intravascular coagulation, death)
• fever, non-haemolytic reactions
• fluid overload
• anaphylaxis and severe allergic reactions
• minor allergic reactions
• minor allergic reactions
• delayed transfusion reactions
• transfusion related acute lung injury (TRALI)

Question 36

what are the possible transfusion transmitted infections?

Answer 36

• bacterial infections: syphilis, pyogenic infections, contamination infections (pseudomonas)
• viral infections: hepatitis (B,C), HIV, west nile virus
• malaria
• vCJD

Question 37

what are possible physiological hazards?

Answer 37

• fluid overload: do not infuse too quickly, transfuse 1 unit over 4 hours if elderly or heart failure, can cause acute pulmonary oedema, treat with diuretics to remove fluid, can transfuse 1 unit over 2 hours in younger patients
• iron overload: haemosiderosis, iron deposited in tissues (liver, heart, pancreas, skin), can treat by iron chelation