principles of blood transfusions Flashcards
how do you determine blood groups?
- 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
how do ABO antibodies occur?
they occur naturally due to cross reactivity with gut bacterial antigens
what are ABO antibodies?
they are IgM (pentameric) antibodies able to fix complement and cause red cell lysis
what happens if you transfuse ABO incompatible blood?
causes intravascular lysis
what happens if you give a life-threatening transfusion?
- shock, hypotension, tachycardia
- renal failure, loin pain, haemoglobinuria
- disseminated intravascular coagulation
- death
what does it mean if you are blood group A?
you have A antigens on the surface of your red blood cells and B antibodies in your blood plasma.
what does it mean if you are blood group B?
you have B antigens on the surface of your red blood cells and A antibodies in your blood plasma
what does it mean if you are blood group AB?
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.
what does it mean if you are blood group O?
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.
what does the lab do when you send a blood sample to them?
1) test the ABO group of the red cells
2) screen the plasma for ‘atypical antibodies’
what are atypical antibodies?
- 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
what is another name for the Coombs test?
anti-globulin test
what is the anti-globulin test?
- uses anti-immunoglobulin antibody to agglutinate red cells
what are the 2 types of anti-immunoglobulin?
- direct (DAT)
- indirect (IAT)
what does direct (DAT) tell us?
- 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
what is indirect (IAT) used for?
- used in the lab for testing blood group antigens
- it can tell us if a patient is positive for Rhesus and other blood groups
what happens if you are rhesus positive?
cannot develop antibodies
what percentage of people are rhesus negative?
15%
what happens if you are rhesus negative?
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
what antibody is generated during rhesus sensistisaiton?
IgG
what is rhesus D sensitisation?
- 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
what are the symptoms of haemolytic disease of the newborn?
- anaemia
- jaundice
- kernicterus (brain damage)
how do you prevent haemolytic disease of the newborn?
- 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
what is in a bag of donated blood?
- red cells
- buffy coat (white cells, platelets)
- plasma (albumin, gamma globulins, coagulation factors)
- water, electrolytes, additives
what does a junior doctor need to know about blood transfusion?
- 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
when do you give a blood transfusion?
- 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)
what are the different types of transfusions?
- 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)
what do you do during pre-transfusion testing?
- 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
what information do you need to request for a blood transfusion?
- 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
what information do you need to put on the sample?
- ID
- signature of phlebotomist
- date
- do not use addressograph labels
- NEVER PRE-LABEL SAMPLE
what do you do for compatibility testing in the lab?
- 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
what is the availability of blood O negative?
- emergency blood
- immediate (5 mins)
what is the availability of blood group that is the same as the patient?
10-15 minutes
what is the availability of fully screened and cross-matched blood?
around 45 minutes
what are the possible reactions of blood transfusions?
- 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)
what are the possible transfusion transmitted infections?
- bacterial infections: syphilis, pyogenic infections, contamination infections (pseudomonas)
- viral infections: hepatitis (B,C), HIV, west nile virus
- malaria
- vCJD
what are possible physiological hazards?
- 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
