Blood groups and blood transfusions Flashcards
1
Q
ABO typing
A
- Karl Landsteiner discovered if he added red cells and plasma of 6 different colleagues the samples would agglutinate
- ABO system is so potently antigenic because the corresponding antibodies to each antigen occur naturally
- ABO antigens are inherited in a mendelian pattern – each group has 25% chance of production, genes code for its enzyme rather than for the sugar itself
- Another gene also codes for the sugar base the ‘A’ or ‘B’
2
Q
ABO antibodies development
A
- Theories they develop against environmental antigens
- Infants <3 months will produce little to no antibodies (maternal prior to this)
- First true antibodies will be >3 months
- Maximal titre 5-10 years
- Titre decreases as we age
- Mixture of IgM and IgG
- IgM mainly for group A and B
- Wide thermal range means they are able to react at 37
3
Q
Rhesus antigens
A
- Over 45 different antigens
- Genetic locus on chromosome 1 (co-dominant allele, 2 genes, RHD (coding for Rh D), RHCE (coding for Rh C and Rh E))
- Highly immunogenic – high proportion of D neg people will form anti-D if exposed to D pos blood
- Can cause haemolytic transfusion reactions and haemolytic disease of the fetus and newborn (HDFN)
4
Q
HDFN
A
- Haemolytic disease of the fetus/newborn
- Rh D sensation most common cause (but there are others)
- Development of antibodies from sensitising event – severe fetal aneamia
- Hydrops fetalis
- Prevention: detect mothers risk, maternal fetal free DNA, anti D prophylaxis
5
Q
cross-matching blood
A
- Units of blood deemed to be suitable will be chosen from the stocks available
- Either an exact match (eg. A+ for A+)
- Or ‘compatible’ blood (eg. O- for A+)
- Serological test
6
Q
Direct Antiglobulin Test (DAT or direct coombs test)
A
- Blood grouping for ABO and rhesus D = indirect antiglobulin test – detecting Ab in patients serum
- Method needed to detect Ab already on RBCs
- Indicated – patients with possible autoimmune haemolysis, transfusion reactions, detecting haemolysis due to fetal/maternal group incompatibility, can be positive for many other reasons too unfortunately (many of which are clinically significant)
7
Q
donation
A
Donation: donors screened, questionnaire, body weight (min 50kg), test for anaemia, temporary and permanent exclusion, either whole blood or apheresis – blood is removed and separated externally and then the components not needed are returned
Tests on donations: mandatory – Hep B, HIV, Hep C, Syphilis, Human T cell lymphotropic virus, groups and antibodies : some are tested for CMV, malaria, west nile virus, typanosoma
8
Q
separation and storage
A
- Whole blood donated into closed system bags
- Blood spun to separate down to packed red cells/ buffy coat and plasma
- Plasma only kept from male donors
- Plasma can be frozen to make FFP (or further processed to make cryoprecipitate)
- Red cells kept at ambient temperature for a short time then passed through a leucodepletion filter and resuspended in additive
- Buffy coats pooled with donations of matching ABO and D type and then leucodepleted to make platelets
9
Q
blood products
A
- Stored at 4◦C, shelf life of 35 days
- Some units will be irradiated (to eliminate risk of transfusion associated graft vs host disease
- Indications: severe anaemia (not purely iron deficiency)
- Transfusion threshold: <70 or <80 if symptomatic, transfuse 1 unit and re-check (unless massive transfusion required)
- Emergency stocks of O Rh D-blood available in certain areas in the hospital (A+E, maternity)
10
Q
platelets
A
- Most units are pooled from 4 donations
- Some single donor apheresis units
- Stored at 22◦C with continuous agitation
- 7 day shelf life if they are monitored for bacterial contamination
- Indications: Thrombocytopenia and bleeding, severe thrombocytopenia <10 due to marrow failure
- ABO type still important (antibodies present in plasma still able to cause recipient red cell haemolysis)
11
Q
fresh frozen plasma
A
- From whole blood donations or apheresis
- From male donors only
- Patients born >1996 , can only receive plasma from low vCID risk (not UK plasma)
- Single donor packs have variable amounts of clotting factor, Pooled versions can be more standardized
- Indications: multiple clotting factor deficiencies and bleeding (DIC), come single clotting factor deficiencies where a concentrate isn’t available
12
Q
Cryoprecipitate
A
- Made by thawing FFP to 4◦C and skimming off fibrinogen rich layer
- Therapeutic dose is 2 packs each pooled from 5 donations of plasma
- Used in DIC with bleeding and massive transfusion
13
Q
Immunoglobulin (IVIg)
A
- Made from large pools of donor plasma
- Normal IVIg: contains Ab to viruses common in the population, used predominantly in immune conditions such as ITP
- Specific IVIg: from selected patients, known high Ab levels to particular infections/ conditions ( anti D immunoglobulin used in pregnancy, VZV immunoglobulin in severe infection)
14
Q
Granulocytes
A
- Used very rarely
- Effectiveness controversial
- For severely neutropenic patients with life threatening bacterial infections
- Must be irradiated
15
Q
Factor concentrates
A
Single factor concentrates:
• Factor VIII for severe haemophilia A (recombinant version which carries no risk of viral or prion transmission)
• Fibrinogen concentrate (factor I)
Prothrombin complex concentrate (Beriplex, Octaplex)
• Multiple factors
• Rapid reversal of warfarin
