the dilemmas of blood transfusion Flashcards
what is a group and screen test
a blood group and antibody screen - conducted in the lab to identify a patient’s ABO and RhD blood group and then to screen the pt’s serum for antibodies against red blood cells
if a pt is blood group A what antibodies will they have in their serum
B antibodies
what does the serum screen look for
AB antibodies and non-AB antibodies -> there are 300 red cell antigens but only few are clinically significant
how long is the serum sample saved for after antibody screening
7 days
when are anti-A and anti-B antibodies produced and in response to what
produce in early childhood (18mo); in response to food antigens and bacteria in the environment
why is ABO incompatibility rarely a problem in pregnancy
Anti-A/B antibodies are IgM antibodies and so very large -> cannot cross the placenta
how do labs test for serum antibodies
by placing the serum in a centrifuge with RBCs of a known antigen and seeing whether agglutination occurs -> antibodies to the specific RBC will cause them to agglutinate, these will stay at the top of the sample as they are too big to spin down through the pores in the gel
i.e. type A RBCs are put in a serum with anti-A antibodies and so will agglutinate, this will not happen in a serum with anti-B antibodies only
blood groups and what antigens are on their RBC
group A - A
group B - B
group AB - A + B
group O - small H (too small to trigger antibody formation)
blood groups and what antibodies are present in their serum
group A - antiB
group B - antiA
group AB - none
group 0 - A + B
as well as ABO grouping, what is tested for in the blood grouping test
Rh D status - also tested for via centrifuge
what is cross-check and who is it not used in
a check using a reverse group which compares the pt’s blood against a known sample -> shows the pt’s serum contains expected antibodies
what is an electronic crossmatch/issue and what must be done prior to its use
the use of a computer to choose suitable units without performing a physical crossmatch in the lab as any unit of ABO + RhD compatible blood can be issued - done after further antibody screening against RBC panels with specific clinically important antigens
what is done if the RBC panel identifies agglutination with clinically significant antibodies
screen against a larger panel to pinpoint the antobody
in pts with RBC antibodies (clinically significant antibodies) what must be done before blood is issued to them
check there is no agglutination reaction in the lab between the pt’s serum and a small quantity of rbcs from the unit wanting to be transfused
how is safety ensured with blood transfusions? (3)
2 group and screen sample records required in the blood bank before ABO-matched blood can be issued; only correctly labeled samples accepted; barcodes and electronic pt identification checked against eachother
what is done in emergency transfusions situations where there are no/only one group and screen records
group O blood is given
what are examples of alternatives to blood transfusion (2)
- increasing RBC production using erythropeitin (EPO), anabolic steroids (e.g. danazol) - may also improve Hb;
- supporting haematopoesis with extra haemantinics (B12, folate, iron)
by how much does Hb typically rise with 1 unit of RBCs
10g/L
what else should be checked prior to transfusion and why
ferritin levels - prevent iron overload
what components is whole blood split up into before it can be transfused
red cells; platelets; plasma; plasma derivatives (non-UK plasma source)
all blood is leucodepleted
process of blood fractionation (6)
- blood is donated;
- blood tested for diseases e.g. HIV, Hep B, syphilis etc.
- filtered to remove leukocytes (leucodepletion);
- platelets removed by plateletpheresis
- fractionated into components -> red cells, pooled platelets, plasma + cyroprecipitate
- components stored for use
how are the components of blood stored and how long is each one useable for
red cells: 4°C, 35 days;
platelets: 22°C kept in an agitator, 5 days;
plasma : -25°C, 36 months
which blood component is usually given in an emergecny and why
red cells - they can be used straight away (no need for thawing)
what should be considered if a massive red cell transfusion is given
pt bleeds out all components and so will need other components of blood too - esp platelets and plasma as this is an important source of clotting factors
what may be triggered in a pt who is bleeding and unstable
massive blood loss protocol
what is given by the blood bank in the massive blood loss protocol
- “packs” of fresh frozen plasma with red cells in set ratios;
- cryoprecipitate and platelets in the second pack if bleeding continues
what will 1 unit of platelets raise the count by
20-30 x10^9/L (not normal level)
do platelets need to be ABO/D identical?
no, but need to be compatible
what is the universal plasma donor group and why
AB - there are no antibodies present
why are people more susceptible to reacting to platelet transfusions
allergic reactions to plasma proteins; bacterial contamination (due to them being kept at room temp)
what pts may need platelet transfusions
pts w a low count who need procedures; are bleeding; are having chemotherapy; thrombocytopenia due to bone marrow failure; abnormal platelet function; multifactorial thrombocytopaenia
what does cryoprecipitate contain
concentrated levels of fibrinogen and factor VIII
what is used in pts who need large amounts of plasma
octaplas -> inactivates any pathogens in large pools of plasma that are made from a large number of blood donors
what factor deficiency is plasma transfusion still used for
rare conditions such as factor V
on average how much plasma is given to a pt
3-4 pools; calculated by their weight
when is fresh frozen plasma used (5)
DIC (disseminated intravascular coagulation) with bleeding; massive transfusion; plasma exchange in thrombotic thrombocytopenic purpura (octaplas); liver disease with abnormal clotting; rare factor deficiencies where factor concentrate is not available
when might somone make antibodies for non-ABO or RhD antigens that they don’t express on their own red cells
after exposure during pregnancy or transfusion
what is an alloantibody
immune antibodies that are only produced following exposure to foreign red blood cell antigens - IgG
what time period must a group and screen sample be taken within to be used in someone who has had a transfusion or been pregnant in the last 3 months
72hrs
what might occur if a pt if transfused w blood containing an antigen for a red cell antibody they have
delayed haemolytic transfusion
consequences of IgG antibody mismatch in pregnancy
I gG antibodies are smaller and so can cross the placenta -> cause haemolyisis of fetal cells -> cause serious haemolytic disease of the fetus/newborn
what can delayed haemolytic transfusion reactions cause (3)
jaundice; fever; poor haemoglobin rise
what can cause transfusion reactions (3)
allergy to foreign plasma proteins; bacterial contamination; incompatible blood transfusion
what can be used to raise Hb levels in renal impairment/myelodysplastic syndrome
erythropoeitin
what drugs should be avoided in pts w thrombocytopenia and why
NSAIDs - impair the function of the remaining platelets
What is haptoglobin
Binds to and transports free Hb
Why do schistocytes form
RBI’s sliced by fibrin strands
