Blood types + transfusion Flashcards
Define ‘group and screen’
blood test to identify ABO + RhD blood group and then screen for antibody against RBCs
Describe group A
A antigen on RBC surface
B antibody
Describe group O
A and B antibodies
small H antigen on RBC surface –> too small to trigger antibody formation
Describe group B
B antigen on RBC surface
A antibody
Describe group AB
A and B antigens on RBC surface
no antibodies
What type of immunoglobulin are anti-A and anti-B?
mainly IgM (do not cross placenta)
What is meant by ‘forward group’ when determining blood group?
using patient’s red cells and monoclonal IgM anti-A, anti-B and anti-D to determine blood group
What is meant by ‘reverse group’ when determining blood group?
using patient’s serum and donor A and B cells to ensure correct antibodies are present (not used in infants as they will not yet have made antibodies)
How would an A+ blood sample show in laboratory testing? (using forward and reverse groups)
agglutination of patient red cells with anti-A antibody
no agglutination with anti-B antibody
agglutination of patient red cells with anti-D antibody
patient’s serum contains anti-B antibodies (agglutination of donor B cells), but no anti-A antibodies
[small RBCs that have not agglutinated can spin down through pores of gel in tube of centrifuge)
What is an antibody screen?
use patient’s serum to screen against panels of all clinically important antigens of other blood groups (eg. Kell, Duffy, Kidd) and the other Rh groups (C, c, E, e)
What is meant by electronic issue/electronic crossmatch?
if no other antibodies are identified on an antibody screen, any unit of ABO-compatible and RhD-compatible cells can be issued with no manual crossmatch
What happens if other antibodies are detected on an antibody screen?
confirm antibody identity using larger panel of cells
provide antigen-negative units
crossmatch with patient’s serum as final check
5 methods to improve transfusion safety
2nd sample required if no previous blood group
compare results with previous blood bank records
no records/1 sample + emergency = group O blood
only accept correctly labelled samples
use barcodes –> ‘closed system’ –> no manual handling/transcription
Describe platelet support
obtained from several donations or via apheresis donation
ABO + RhD compatible (not identical)
stored at 22 degrees C
short shelf life 5-7 days
breeding ground for germs
1 unit (bag) at a time –> raise platelet count 20-30x10^9/L
give over 20 mins
beware reactions
Which patient groups might need platelets?
thrombocytopenia due to failure of marrow production (eg. after chemotherapy)
functional platelet disorder (numbers may be normal) with bleeding (eg. inherited platelet disorder)
‘dilutional’ thrombocytopenia (eg. from massive bleeding)
thrombocytopenia which is multifactorial + associated with bleeding (eg. liver disease)
What are ‘safe’ platelet counts in adults for dental extraction, lumbar puncture, major surgery, epidural and neurosurgery/ophthalmic surgery?
dental extraction = >30x10^9/L
lumbar puncture = >40x10^9/L
major surgery = >50x10^9/L
epidural = 80x10^9/L
neurosurgery/ophthalmic surgery (other than cataracts) = >100x10^9/L
Describe plasma support
fresh frozen plasma (FFP) contains all clotting factors
can be further refined to cryoprecipitate (high in factor 8 + fibrinogen)
can be ‘pathogen inactivated’
superseded in majority of uses by manufactured coagulation concentrated
volume approx. 300ml
sourcing from UK
12-15ml/kg adult dose (approx. 3-4 bags)
stored at -30 degrees C
shelf life = 1 year
ABO compatible
~20 mins to defrost
Indications for use of FFP
DIC with bleeding
massive transfusion (check clotting)
plasma exchange in thrombotic thrombocytopenic purpura (octaplas)
liver disease with abnormal clotting
some rare factor deficiencies where no factor concentrate available
not for reversal of warfarin (use prothrombin complex concentrate eg. Beriplex)
Describe red cell alloantibodies
most patients only have anti-A or anti-B
other antibodies can be acquired during pregnancy or transfusion (red cells only matched for ABO + RhD)
100s of other antigen groups like Kell, Duffy, Kidd etc. which are not matched for when transfusing
more blood a patient receives , increased likely an alloantibody (IgG) is formed to a red cell antigen
What do patients with red cell antigen antibodies need/have?
risk of delayed haemolytic transfusion reactions
may form other antibodies (72 hour rule)
if a pregnant woman, can experience haemolysis of foetal red cells
need blood ‘cross-matched’ (their serum v. donor red cells) to ensure compatability
are not suitable for electronic issue
Severe transfusion reactions examples
anaphylaxis
bacterial contamination
acute + delayed haemolysis
(greatest risk = getting wrong blood component, ABO incompatibility can be rapidly fatal)
Name an alloimmune cause of haemolytic anaemia
haemolytic disease of the newborn/rhesus disease
