blood transfusion n Flashcards
wwhat are the major ABO blood groups *
A - AA/AO
B - BB/BO
AB - AB
O - OO (recessive)
where do you get blood from
human source - no synthetics yet - human source so not risk free
it is a scarce resource, 1 donor gives 1 pint - max every 2-4 months - we need 9000 units of blood/day in uk and cant stockpile it because blood shelf life is only 5 weeks
when do we use blood
when there is no safer alternative eg if massive bleeding (1L) plain fluids will not be sufficient
if anaemic - iron/B12/folate alone is not appropriate - if you can replace any of these directly then this is better because they can malke up the rest themselves
describe ABO blood groups *
this is the most important opf all blood groups - people die if you get it wrong
A and B antigens on red cells are formed by adding onee or other sugar residue onto a common glycoprotein and fucose stem on a red cell membrane
n-acetylgalactosamine is added to A
galactose residue is added to B
all red cells have H antigen - this is the common antigen
consequences of ABO groups *
if you dont have the antigens the body recognises them as foreign and makes antibodies
how are the blood groups made *
they are controlled by genetics
A gene codes for enzyme that adds N-acetyl galatosamine to common glucoprotein and fucose stem
B codes for enzyme that attches galactose stem
A and B genes are codominant
O gene is recessive - codes for nothing, noting is added to H
describe the formation of Ab against te ABO groups, and the siggnificnace of the type of Ab *
Ab against the antigen not present in blood
they are made from birth - because from birth you are exposed to bacteria that make proteins similar to A and B - body makes Ab against these that then attack ABO antigens
they are IgM Ab - complete Ab so fully activates complemet to the membrane attack complex - make holes in the red cell membrane = release of Hb and BR = jaundic e- induces cytokine storm - reduction in BP = shock
in lab tests - Igm Abs interact with ag to form agglutins - agglutination is seen as clumping and shows the blood types are incompatable
which blood group can give to anybody *
O
what blood group cna get blood from anybody *
AB - no Ab
when we transfuse it is only the red cells that is transfused not the plasma so teh Ab in donated blood doesnt matter
describe how you test for ABO blood groups *
take patient blood sample with plasma and cells
centrifuge so cells are at bottom - but cells in bottom of well
ABO group test with known anti-A and anti-B
anti-a soln is blue to avoid error, anti-b is yellow
if there is a clump - those red cells have the matching antigens ie a antigens with anti-a
test your plasma to see what ab are present
select donor with the right grroup - ie have the same antigens
cross match - mix bit of patient’s serum with donor red cells- there should be no reaction - if there is agglutination blood is incompatible
this is all automated
what are the RH blood groups *
RhD is most important - most immunogenic after ABO
have RhD positive or negative
what are the genes for RhD
D - codes for D antigen on the red cell surface membrane
d - codes for no antigen - recessive
dd = no D antigen = D -ve 15%
DD/Dd = D +ve 85%
describe the formation of anti-D Ab *
made by people wo are D -ve
have to have 1st exposure eg pregnancy or transfusion - when fine
on 2nd exposure the Ab detect this and cause effects
describe the anti-D Ab and which groups make them *
IgG
D +ve have antigens - cant make the ab
-ve - dont have the ag so if exposed - make the ab = problems on second exposure
what are the impilcations of anti-D ab *
patients with anti-d ab must have d - ve blood - otherwise ab attack transfused blood = delayed haemolysis (5-10 days after transfusion) dont activate the whole complement pathway - only as far as CD3 = anaemia - plasma Hb causes renal failure , high BR = jaundice
in pregnancy - if RhD -ve mother and RhD +ve father - if foetus is RhD - IgG Ab cross placenta give mother 1st exposure (fetomaternal leakage of red cells across the placenta occurs at delivery, silent bleeds are not uncommon during late pregnancy) - if 2nd preg is RhD +ve - IgG from mother pass through placenta and destroy red cell in foetus - anaemia - in pregnancy the rise in BR can be taklen out by placenta, or cross the BBB = brain damage causes hyperextension of the arms, legs and neck and death (BR stain the brain columns) - if anaemia severe die in pregnancy becuase not enough O2 transportation so eart work faster = HR
