Principles of Blood Transfusion Flashcards
ABO antibodies
These are IgM pentameric antibodies able to fix complement & cause red cell lysis.
Transfusion of ABO incompatible blood causes intravascular lysis.
Can lead to life threatening transfusion reaction:
- shock, hypotension, tachycardia, renal faiilure, haemoglobinuria, disseminated intravascular coagulation, death
Blood Groups
A: have A antigens on rbcs and B antibodies in plasma
B: have B antigens on rbcs and A antibodies in plasma
AB: have AB antigens and no AB antibodies
O: have neither A or B antigens, but both A and B antibodies
O is also protective against Covid
Group and Screen
Test ABO group of red cells, and screen plasma for atypical a.b.s
Atypical antibodies arise due to sensitisation with foreign red cell antigens caused wither by previous transfusions or pregnancy.
They can cause blood transfusion reactions if incompatible blood.
The Coombs Test (or anti-globulin test)
Uses anti-immunoglobulin antibody to agglutinate rbcs
2 types - direct (DAT) and indirect (IAT)
DAT tells us if rbcs are coated with antibody - it is positive after transfusion reaction and in HDN and in autoimmune haemolytic anaemia
IAT is used for testing blood group antigens and can tell us if a patient is positive for Rhesus/other blood groups// looks for antibodies in the blood caused by a transfusion or incompatible blood
Rhesus System
Rh positive people cannot develop antibodies
15% people are Rh negative, so can develop antibodies is they are transfused with Rh +ve blood/are pregnant with Rh +ve baby
This is called Rhesus sensitisation and the antibody generated IgG type
The most important antigen is RhD
Rhesus D sensitisation
People who develop Rh antibodies can’t be given the Rh +ve blood
If a mother (Rh -ve) is pregnant with Rh+ve foetus, she may produce antibodies that harm the baby
This is haemolytic disease of the newborn -> anaemia, jaundice & kernicterus
HDN Prevention
Pregnant women have ABO and RH blood group check at week 12
Rh -ve women receive anti-D antibody im injection at 28 and 34 weeks, preventing Rh D sensitisation
Baby tested at birth - if Rh +ve, mother receives further anti-D until Kleihaur test becomes negative
If already sensitised, foetus requires monitoring via trans-cranial Doppler scan and may require intra-uterine transfusions, if sighs of anaemia
When to give a blood transfusion
Severe acute blood loss - trauma/GI blood loss?obstetric blood loss
Elective surgery associated with sig blood loss
Medical transfusions - cancer chemo, renal failure
Anaemia - bone marrow failure, haemoglobinopathy
What Type?
Blood components - rbcs, platelets, plasma, fibrinogen
Plasma derivatives - immunoglobulins, coagulation factors, albumin
Cell salvage and autologous transfusion - rare
Components in bag of blood: red cells; buffy coat, wbcs & platelets; plasma, albumin & gamma globulins & coag factors; water, electrolytes, additives
Compatibility Testing
Establish ABO and Rh group
Check for atypical antibodies in patient serum
Select donor blood
Testing between donor cells and patient serum
Request information about ID, blood group, previous transfusions, reason…
Blood Availability
O negative - emergency blood (5 minutes)
Group compatible (10-15 minutes)
Fully screened and cross matched (45 minutes)
Blood Transfusion Reaction
Major ABO incompatibilities (acute renal failure, disseminated intravascular coag, death)
Febrile non-haemolytic reactions
Fluid overload
Anaphylaxis and severe/minor allergic reactions
Delayed transfusion reactions/related acute lung injury
Transfusion Transmitted Infections
Bacterial: syphliis, pyogenic infections, contamination
Viral: Hep B/C, HIV, HTLV, CMV, West Nile virus
Malaria of vCJD
Physiological Hazards
Fluid Overload: don’t infuse too quickly, 1 unit/4 hours, can cause acute PE, treat with diuretics to remove fluid, 1unit/2 hours in younger patients
Iron Overload: haemosiderosis = iron overload, iron deposited in tissues - liver, heart, pancreas, skin, treated by iron chelation
