Transfusion Flashcards
minimum criteria for being a blood donor?
haemoglobin
- 135 g/L in men
- 125 g/L in women
50kg weight
what happens to donated blood once received?
whole blood is centrifuged to separate into component parts
samples then undergo microbiological testing
what microbiological tests are done on donated blood?
HIV Hep B Hep C Hep E HTLV syphilis
how are blood components stored?
red cells = 4 degrees for 35 days
FFP = stored at -30 degrees for 3 years
platelets = stored at 22 degrees for 7 days with agitation
what products are available from transfusion labs
blood components (red cells, FFP, platelets, cryoprecipitate) blood products (anti-D, prothrombin complex concentrate) blood products from pharmacy (IV Ig, human albumin, specific Ig)
what determines the blood type?
antigens on red cell surface
describe the ABO system of blood typing
found on chromosome 9
A and B genes encode for transferases which modify precursor called H substance on red cell membrane
how do A, B and O interact?
A and B are both dominant over O
and B are codominant
O is silent
which ABO types are most common?
O = 47% A = 42% B = 8% AB = 3%
which antigens are present on red cell surface in each blood group?
A = A antigens B = B antigens AB = A and B O = neither
phenotype vs genotype?
phenotype = which antigens are detected
genotype = which genes are present
e.g
- phenotype = group O, genotype = OO
- phenotype = group A, genotype = AA or AO
- phenotype = group B, genotype = BB or BO
- phenotype = group AB, genotype = AB
how is ABO inherited?
one ABO gene from each parent
eg - mother = AO, father = BO - children can be AB, AO, BO or OO
what is Landsteiner’s law?
when an individual lacks the A or B antigen, the corresponding antibody is produced in their plasma
naturally occurring antibodies cause haemolysis of red cells expressing the specific antigen
this makes ABO the most clinically significant blood group system
which antibodies are present in each blood type?
A = anti B B = anti A AB = neither O = anti A and anti B
who can group O donate to/receive from?
can donate to everyone
can only receive from group O
who can group A donate to/receive from?
can donate to A
can receive from O and A
who can group B donate to/receive from?
can donate to A and AB
can receive from B and O
who can group AB donate to/receive from?
can donate to AB
can receive from all groups
what is the 2nd most important antigen present on RBCs after A/B?
RhD
85% of people are RhD positive
describe RhD antigens?
2 alleles - D and d - D is dominant, d is silent inherit one from each parent RhD +ve = DD or Dd RhD -ve = dd
clinical significance of RhD antigen?
very immunogenic
anti-D antibody can cause transfusion reactions and haemolytic disease of the newborn
should avoid exposing RhD negative people to D antigen through transfusion
how can individuals be sensitised to exposure to foreign antigens?
pregnancy
transfusion
(repeat exposure may result in transfusion reaction)
what are the aims of pre-transfusion testing?
identify ABO and RhD group of patient
identify presence of clinically significant red cell antibodies
allow selection of appropriate blood for transfusion
how can ABO group be determined?
test patient’s red cells with anti-A, anti-B and anti-D antisera (identifies antigens on red cells via direct agglutination with IgM)
or
test patients plasma against reagent red cells of group A and group B (identifies antibodies in the plasma)
how do antibodies and antigens on red cells interact?
cause agglutination
how can antibody screening be done in blood?
test patient’s plasma against several reagent red cells which express a known range of antigens
- identifies antibodies in the plasma
- use the direct anti-globin test
what is the indirect anti-globulin test?
addition of anti-human globulin (AHG) to plasma/red cell suspension facilitates red cell agglutination
what is the indirect anti-globulin test?
reagent red cells expressing known antigen(s)
patient plasma is added
anti-human globulin is added
look for agglutination (indicates presence of an antibody)
how is blood selected for transfusion?
matched for, or compatible with, patient’s ABO and RhD group
consider presence of RBC antibodies
perform crossmatch to check donor cells are compatible with patient plasma
how is an IAT crossmatch performed?
donor red cells in test tube patient plasma is added anti-human globulin is added look for agglutination - agglutination = donor cells are incompatible with patient plasma - no agglutination = compatible
indications for RBC transfusion (rather than tablets)?
symptomatic anaemia with Hb <70g/L (80g/L if cardiac disease also present)
major bleeding
transfuse a single unit of RBCs and then reassess
indications for platelet transfusion?
prophylaxis in patients with bone marrow failure and very low platelets
treatment of bleeding in thrombocytopenic patient
prophylaxis prior to surgery/procedure in thrombocytopenic patient
indications for fresh frozen plasma (FFP) transfusion?
treatment of bleeding in patient with coagulopathy (PT ratio >1.5)
prophylaxis prior to surgery or procedure in patient with coagulopathy (PT ratio >1.5)
management of massive haemorrhage (trauma)
not in absence of bleeding/planned procedure
how is a transfusion requested?
multi-step process correct labelling of sample - name, ward, gender, DOB, date and time of sampling, CHI number, signature document consent for transfusion blood authorisation document document transfusion and return to lab
how is transfusion monitored?
observations before blood is commenced
observations at 15 mins
observations within 60 mins of completion
