Haem 11 Flashcards
Where is blood from for donation
Human source - no synthetics yet (research) - not risk free
When is blood used
When no safer alternative
If massive bleeding - if ‘plain fluids’ not sufficient
If anaemic - if iron/ B12/ folate not appropriate
Outline the basis of blood group
All have common H antigen:
A has galnac added on
B has gal added on
AB has some with either, O just has H stem
What are antigens determined by
Antigens determined by corresponding genes
A gene codes for enzyme which adds N-acetyl galactosamine to common glycoprotein and fucose stem
B gene codes for enzyme which adds galactose
Inheritence of O
It is receissive, so must have 2 O groups if you are blood group O
Possible blood group for A
AA, or OA
Which antibodies do you have against antigens
Person has antibodies against any antigen NOT present on own red cells
What type of antibody is made against the blood cell antigens that you do not have
Naturally occurring (nearly from birth) - IgM: it is a ‘complete’ antibody, so:- fully activates complement cascade to cause haemolysis of red cells
(pentameric so it cross links, activates complemet, and causes MAC and punches holes in the red cell membranes, and cytokine storms)
Group A given to group O patient
blood group A given to patient who is group O - so has anti-A and anti-B - then antibody/ antigen interaction often fatal
What i shown in tests to determine blood group
In laboratory tests, IgM Abs interact with corresponding ag to cause agglutination eg: if patient is group B, he has anti-A antibody in plasma - when add to group A cells - agglutination seen (clump) - shows cells are incompatible
How is ABO blood group determined (slide 9)
Commonest blood group in UK
O, A, B and AB
Which antibodies for each blood group
A: anti B
B: Anti A
O: Anti A and Anti B
AB: none
What is the Cross match
Final check, adding patient’s plasma to the blood you are going to transfuse to ensure it doesnt agglutinate
What types of RH groups
RhD is most important
What are the types of RhD groups
RhD positive or RhD negative
What are the potential genotypes for RhD positive and RhD negative
RhD +ve: DD or Dd
RhD -ve: dd
Most RhD positive in UK
How are antibodies made against RhD in RhD negative people
RhD-ve people CAN make anti-D antibodies AFTER they are exposed to the RhD antigen - either by transfusion of RhD positive blood or in women, if they are pregnant with an RhD positive fetus
What type of antibodies made against RhD antigens
IgG antibodies
What is the consequence of IgG coating of the RhD antien
Not MAC, but complex recognised by spleen, and has membrane pinched out, leading to spherocytes and then are taken out second time around… causes delayed haemolytic transfusion reaction - anaemia; high bilirubin; jaundice etc
Implications of anti-D antibodies (antibodies aginst RhD postiive)
- Future transfusions
- Haemolytic disease of the newborn (HDN)…
if RhD neg mother has anti-D - and in next pregnancy, fetus is RhD pos - mother’s IgG anti-D antibodies can cross placenta - causes haemolysis of fetal red cells - if severe: hydrops fetalis; death
Why isn’t RhD neg given to RhD positive people
no harm to give RhD neg to a pos patient - just wasteful
What blood group can be used for everyone
O neg used as emergency blood when patient’s blood group not known (NB only 6-7% of donors are O neg)
….
What other antigens can be present on red cells, do they matter
Don’t routinely match blood for all these, eg Rh group -C, c, E, e; others - Kell, Duffy, Kidd, etc
about 8% of patients transfused will form antibody to one or more of these antigens…..
It is important….
Once have formed antibody must use corresponding antigen negative blood; or else risk of delayed haemolytic reaction (can be severe)
What is done to avoid the delayed haemolysis associated with these other antibodues
as well as testing their ABO and RhD group BEFORE each transfusion episode, test patient’s blood sample for red cell antibodies
you need to do a new one each time
Questions on slide 16
Cannot be AB or O
Components of blood
How much is collected from each donor
Why is blood not kept as whole blood
Why is red cells + plasma not given to patients needing RBC
What layers appear after centrifugation of blood
1 unit (‘pint’) blood collected into a bag containing anticoagulant
Whole blood not given:
- more efficient, less waste
- some components degenerate if stored as whole blood
Red cells – concentrated, as plasma
removed; also avoids fluid overloading patients
Split one unit of blood by centrifuging whole bag (red cells bottom, platelets + leukocytes middle (=buffy coat), plasma top) then squeeze each layer into satellite bags and cut free (closed system)
What can whole blood be used to make
- Red cells
- Platelets
- Plasma
Why would you use cryoprecipitate
it’s fibrinogen rich
What can you do with plasma
-into fresh frozen plasma (FFP) or cryopreciptate, or plasma for fractionation, in which you pool thousands…
What can plasma for fractionation be used for
Can take out albumin, factor VIII, IX immunoglobulins, anti-D etc.
Shelf life of the red cells
Shelf life 5 weeks; stored at 4oC (fridge)
1 unit from 1 donor - ‘packed cells’ (fluid plasma removed)
How are red cells given
Give through a ‘blood giving set’ - has filter to remove clumps/debris
What are frozen red cells needed for
for rare groups/ antibodies - poor recovery on thawing, rare… but you lose some red blood cells
Fresh frozen plasma how much from each donor
1 unit from 1 donor (300ml) can get small packs for children
How is FFP stores and shelf life
Stored at -30oC (frozen within 6h of donation to preserve coag factors)
Must thaw approx 20-30 mins before use (if too hot, proteins cook)
What dose of FFP needed
Dose 12-15ml/kg = usually 3 units
What is needed to match FFP
Need to know blood group - no x-match, just choose same group (as contains ABO antibodies from donor, which could cause a bit of haemolysis with receipient cells
When is FFP needed
- If bleeding + abnormal coag test results (PT, APTT)
- Monitor response - clinically and by coag tests
- Reversal of warfarin (anticoagulant) eg for urgent surgery (if PCC not available= Prothrombin complex concentrate, also known as factor IX complex, is a medication made up of blood clotting factors II, IX, and X. Some versions also contain factor VII. It is used to treat and prevent bleeding in hemophilia B if pure factor IX is not available.. )
- Other conditions occasionally
Cryoprecipitate storage
Same as FFP - store at -30oC for 2 yrs
Standard cryoprecipitate dose
Standard dose = from 10 donors (can split into 5 in each pack and give two bags)
Important feature of cryoprecipitate
Contains fibrinogen and factor VIII
Indication for cryoprecipiate
If massive bleeding and fibrinogen very low
Rarely hypofibrinogenaemia
How many donors needed for a pool of platelets
4 donors
or from 1 donor by apheresis (cell separator machine)
Shelf life of platelets
Shelf life 5 days only - (risk of bacterial infection)
What info is needed for platelet
Blood group:
No cross-match, just choose same group (as platelets have low levels of ABO antigens on, so wrong group platelets would be destroyed quickly) - and can cause RhD sensitisation, as some red cell contamination
Indications for platelets
Mostly haematology patients with bone marrow failure (if platelets <10 x 109/L)
Massive bleeding or acute DIC
If very low platelets and patient needs surgery
If for cardiac bypass and patient on anti-platelet drugs
How much plateltet is needed usually
1 pool
Which cotting factors affected by warfarin
2, 7, 9 and 10
How does fractionated plasma work
Fractionated (like oil)
What can be gleaned from fractionated plasma ..
Factor VIII and IX,
Immunoglobulins and albumin
When is factor VIII and IX needed from fractionated products
For haemophilia A and B respectively (males)
Factor VIII for von Willebrand’s disease
Heat treated - viral inactivation
Recombinant factor VIII or IX alternatives increasingly used, but expensive
When are immunoglobulins needed from fractionated products
IM: Specific - tetanus; anti-D; rabies
IM: Normal globulin - broad mix in population (eg: HAV)
IVIg – pre-op in patients with ITP or AIHA
When is albumin needed and at what dose
4.5%
Useful in burns, plasma exchanges, etc
Probably overused (not indicated in malnutrition)
20% (salt poor)
For certain severe liver and kidney conditions only
WHat does cross matching involve
X-match: patient’s serum mixed with donor red cells - should not react
WHat proportion of people have RhD negative and which proportion RhD positive blood
85% of people are RhD positive; 15% are RhD negative
