ABO blood groups Flashcards
what are the two important blood group antibodies in the ABO system
igM and igG
properties of igM
Pentameric structure
10 antigen binding sites
Red cells repel one another and do not come closer than within 12 nm of one another
A single IgM antibody can bridge the gap and cause agglutination of red cells
properties of igG
Monomeric structure
2 antigen binding sites
Binding site can only reach 10 nm apart
A single IgG antibody cannot cause agglutination of red cells
what antibody can pass the placenta
igG
which antibody binds complemet
igM
what do igG antibodies do
Primarily cause the removal of red cells by extravascular haemolysis (Fc regions of red cell bound IgG interacts with Fc Receptors on macrophages of reticuloendothelial system).
what antibody is the main ABO blood group antibody
igM
what are the percentages of ABO blood groups in the UK
Group O 47%
Group A 42%
Group B 8%
Group AB 3%
what do the ABO blood group genes code for
glycosyltransferase enzymes
what are the ABO genes
H gene
A gene
B gene
where is the H gene located
chromosome 19
where are the A and B gene located and what is important about it
both on chromosome 9, are co-dominant alleles
what does the H gene code for
H enzyme (H substance=O)
What do A and B genes code for
A enzyme or B enzyme
what does the terminal carbohydrate added to the H substance depend on
enzyme coded
briefly describe the ABO genetics
precursor substance + H gene = H substance
+ A gene = A substance
OR
+ B gene = B substance
what are the ABO subgroups and frequency
A1- 80%
A2- 20%
what is the possible genotypes for blood group A1
A1A1, A1A2, A1O
what is the possible genotypes for blood group A2
A2A2, A2O
what is the possible genotypes for blood group A2B
A2B
which A subtype is dominant and which is recessive
A1- Dominant
A2- recessive
what is the difference between subgroups A1, A2 and A2B
The difference is largely a quantitative one, but may be qualitative in some cases where anti-A1 is produced.
ABO antibodies and antigens are present at birth, true or false
ANTIBODIES - FALSE
antibodies develop within the first 4 months an dreach max at 5 years
ANTIGENS - PARTIAL
antigens are not fully developed at birth- development over first 1-2 years
what are the suggested possibilities of where ABO antibodies come back
Some immunoglobulin just happens to ‘fit’. (c.f. Lectins)
Via maternal milk
From environmental factors (Experiments with chickens)
Genetic basis
where are antibodies and antigens within the blood
antigens are on the red cells
antibodies are in the plasma
what antigens/antibodies does blood group O have?
Antigens- none
Antibodies- anti-A and anti-B
what antigens/antibodies does blood group A have?
Antigens- A
Antibodies- anti-B
what antigens/antibodies does blood group B have?
Antigens- B
Antibodies- anti-A
what antigens/antibodies does blood group AB have?
Antigens- A and B
Antibodies-none
how many rhesus antigens are they and name them
5
- D
- C
- c
- E
- e
what does the RhAG gene do and where is it found
chromosome 6
The unlinked RhAG gene on chromosome 6 incorporates the antigen into the cell membrane
where is the RhD gene found
chromosome no 1
frequencies of RhD in the UK
85% RhD positive
15% RhD negative
what are the variations of Rh D groups
Weak D
Partial D
what is weak D
Possesses all of a normal D blood group, but has quantitatively less
Is Rh positive as a donor, patient and an antenatal patient.
Cannot produce anti-D
what is partial D
Lacks part of a normal D blood group
Can produce anti-D
Can cause the production of anti-D in a D negative recipient
Regarded as Rh pos as a donor
Rh neg as a recipient
Antenatal patients require anti-D prophylaxis
how are the Rh antigens inherited
as a group of 3 antigens which are inherited together
C and c antigens are alleles
E and e antigens are alleles
There is no d antigen, Rh negative individuals lack the D antigen
what are 1st order Rh combinations, include short hand
CDe R1
cDE R2
cde r
what are 2nd order Rh combinations, include short hand
Cde r’
cdE r’’
what are 1st order Rh combinations in black people, include short hand
cDe Ro
rare in white people
what are the rare and extremely rare Rh combinations, include short hand
CDE RZ Rare
CdE ry Extremely rare
What is the major cause of Haemolytic Disease of the Newborn (HDN)
Anti-D
how does anti-D come about
Produced in women as a result of sensitisation by red cells from D positive fetus
May be produced in males as a result of transfusion with D positive blood.
facts about anti-c
Clinically significant
Relatively common
May cause HDN or HTR
Often found together with anti-E
facts about anti-E
Clinically significant Relatively common May cause HDN or HTR Less clinically significant than anti-c Often found together with anti-c in individuals who lack c and E antigens
facts about anti-C
Clinically significant
Relatively common, often seen with anti-D
May cause HTR
HDFN rare when on its own
facts about anti-e
Clinically significant
May cause HTR
how do we prevent Rh antibody production
Type patients for full Rh groups and match the donations. This is important for:
All female patients under 60 yrs of age
Patients who may need regular transfusions (e.g. Sickle cell disease)
Patients who have already produced other antibodies
what is Haemolytic disease of the Newborn (HDN)
An illness in fetuses and newborn infants caused by a blood group antibody in the mother attacking red cells in the infant which carry the corresponding antigen inherited form the father.
The most potent disease results when the mother is Rh D negative and the fetus is Rh D positive
how does HDN come about
1st pregnancy fine
during delivery - small quantity or red cells transferred from fetus to mother
Mother is sensitised to foreign red cell antigens on fetus
Antigens more fully developed on foetal cells more likely to cause sensitisation
Subsequent pregnancy-
antibodies transferred from mother to baby
what is the test for diagnosis of HDN
Direct antiglobulin test on cord blood.
Detects IgG antibody bound to the surface of the infant’s red cells.
what is the treatment of HDN depending on results of diagnostics?
Mild – Phototherapy under UV light
Moderate – Top up or exchange transfusion
Severe – Exchange transfusion or IUT
Treatment - Requirements for IUT / exchange transfusion red cells
5 days old or less, CPD red cells CMV negative Sickle cell negative Negative for any red cell antibodies Low level of anti-A and anti-B Gamma irradiated Hct 0.5 – 0.6 for ET up to 0.7 for IUT
prevention of HDN?
Known that ABO offered some protection Standard dose of prophylactic anti-D 500 i.u. up to 4ml bleed 1250 i.u. up to 10ml bleed Antenatal prophylaxis Monoclonal anti-D
what is the International Society for Blood Transfusion view on antibody identification
No antibody investigation technique or combination of techniques can be guaranteed to detect all red cell antibodies.
what are the British Committee for Standards in Haematology Guidelines for Compatibility Procedures in antibody identification
The specificity of the antibody should only be assigned when it is reactive with at least two examples of reagent cells carrying the antigen and non reactive with two examples lacking the antigen
what are the Characteristic properties of a red cell antibody investigation panel.
Identify a single antibody Separate common mixtures If possible in a single pass Not give the same pattern of results with two different antibodies Give “confidence” in the findings
what are the significant factors of an Antibody risk assessmentfor transfusion
ABO Rh (all of them!) Kell system Kidd system Duffy system anti-M 37oC active Anti-S, -s
what are the three main factors forAntibody risk assessment for HDFN
Anti-D
Anti-c
Anti-K
what is classed as the gold standard in antibody identification and what does it include
Indirect Antiglobulin Technique
detects 37oC active antibodies
detects IgG antibodies
detects complement fixing antibodies
Detects all Rh antibodies, anti-K, k, Fya, Fyb, Jka, Jkb, M (reactive at 37 deg C), S, s, Kpa, Kpb, Lua, Lub
what is the Indirect Antiglobulin Technique (IAT)
Antigen – Antibody complex forms
(Reagent Red cells (known phenotype) + Antibodies in patient’s plasma)
AHG added
(Anti-Human Globulin)
Agglutination seen
Enzyme treated cell techniques (Papain) features
good for all Rh antibodies and anti-Jka, Jkb, Lea, Leb, P1
do not detect anti-Fya, -Fyb, -M, -N, -S because these blood groups are destroyed by papain
excellent in resolving mixtures
what are the different techniques for identifying antibodies
Enzyme treated cell techniques (Papain
Saline 20oC
other:
PEG IAT, 2-stage IAT, enzyme IAT,
Capture R, albumin displacement, polybrene,
37oC saline, 31oC saline 4oC saline,
NISS, LISS, BLISS, adsorptions, elutions, neutralisations………….
Saline 20oC technique features
Saline 20oC
detects IgM antibodies, e.g anti-M, N, P1, Lea, Leb, H, I and ABO
detects usually clinically insignificant antibodies (ABO antibodies excepted)
detects antibodies which may give unclear IAT
good for resolving mixtures
antibody identification criteria
To be certain of the identification of an antibody the panel used must give
Positive results against two cells which contain the antigen
Negative results against two cells which lack the antigen
Exclude the presence of any other antibodies
Antibody mixturesHow do you know it’s a mix?
No fit for a single specificity, auto negative
? Different strengths of reactions
? Different patterns with different techniques?
Additional reactions to those in previous sample
How to identify elements of a mixture
Getting some negative results? Try to identify at least one component (there’s usually some Rh in there) Use negatives to eliminate something! Try to find more negatives
How does the phenotype help
to identify elements of a mixture (antibody identification)
Tells you what alloantibodies patient can form Helps you to find more panel cells May help in providing safe transfusion BEWARE The transfused patient The “untransfused” patient The Positive Direct Antiglobulin Test
RCI Molecular RBC Typing facts
Can provide a full genetic type for highly prevalent antigens
Simple 3 step procedure with minimal ‘hands-on’ time, giving results in under 3 hours
Most technology (PCR cyclers) already present in H&I laboratories
Specialised Reader
Clinical Value of Molecular RBC Typing
DAT positive patients Multi-transfused patients Patients with pan-reactive autoantibody that resists absorption procedures Patients with weak expression of antigen Where liquid reagents are unavailable
RBC Genotyping
Extract DNA (30 mins)
Prepare tests - microplate (10-30 mins)
Amplify DNA – thermocyclers (c2 hours)
Analysis (10 mins)
TaqMan Probe PCR-SSP
steps
- Assay components an DNA technique
- Denatured template and annealing assay components
- Polymerisation and signal generation
TaqMan Probe PCR-SSP
workflow
Samples processed in a single day
3 Samples per run, up to 8 runs a day
Results available in approx 2.5 hours
Good reliability with low failure rate
advantages of TaqMan Probe PCR-SSP
Most useful in multi-transfused and AIHA cases
Results can be obtained the same day
Reproducible, Low fail rate
Good concordance with serological typing results
Simple to use and not labour intensive
No significant wastage
Direct download of results
disadvantages of TaqMan Probe PCR-SSP
Not suitable for urgent cases
Not as fast as serological typing (see urgent cases above)
Not suitable for rare genotypes – require sequencing
ABO – simple serologically but complex genetically (not performed on this assay).
