Description
Which blood type is considered the universal donor, AND WHY. 150 WORDS
Unformatted Attachment Preview
JPAC
Joint United Kingdom (UK) Blood Transfusion and Tissue
Transplantation Services Professional Advisory Committee
PDF Generated
14/01/2024 20:01
Transfusion Handbook
2: Basics of blood groups and antibodies
http://www.transfusionguidelines.org/transfusion-handbook/2-basics-of-blood-groups-and-antibodies
Please note the Transfusion Handbook has not been updated since 2014 and requires review.
Guidance within the Handbook may therefore be out of date with other current guidelines.
Contact [email protected] for more information.
2: Basics of blood groups and antibodies
Essentials
ABO-incompatible red cell transfusion is often fatal and its prevention is the most important step in clinical
transfusion practice.
Alloantibodies produced by exposure to blood of a different group by transfusion or pregnancy can cause
transfusion reactions, haemolytic disease of the fetus and newborn (HDFN) or problems in selecting blood
for regularly transfused patients.
To prevent sensitisation and the risk of HDFN, RhD negative or Kell (K) negative girls and women of childbearing potential should not be transfused with RhD or K positive red cells except in an emergency.
Use of automated analysers, linked to laboratory information systems, for blood grouping and antibody
screening reduces human error and is essential for the issuing of blood by electronic selection or remote
issue.
When electronic issue is not appropriate and in procedures with a high probability of requiring transfusion a
maximum surgical blood ordering schedule (MSBOS) should be agreed between the surgical team and
transfusion laboratory.
There are more than 300 human blood groups but only a minority cause clinically significant transfusion
reactions. The two most important in clinical practice are the ABO and Rh systems.
Please note the Transfusion Handbook has not been updated since 2014 and requires review.
Guidance within the Handbook may therefore be out of date with other current guidelines.
Contact [email protected] for more information.
page 1 of 7
Transfusion Handbook / 2: Basics of blood groups and antibodies
2.1: Blood group antigens
Blood group antigens are molecules present on the surface of red blood cells. Some, such as the ABO
groups, are also present on platelets and other tissues of the body. The genes for most blood groups have
now been identified and tests based on this technology are gradually entering clinical practice.
Please note the Transfusion Handbook has not been updated since 2014 and requires review.
Guidance within the Handbook may therefore be out of date with other current guidelines.
Contact [email protected] for more information.
2.2: Blood group antibodies
These are usually produced when an individual is exposed to blood of a different group by transfusion or
pregnancy (‘alloantibodies’). This is a particular problem in patients who require repeated transfusions, for
conditions such as thalassaemia or sickle cell disease, and can cause difficulties in providing fully
compatible blood if the patient is immunised to several different groups (see Chapter 8). Some antibodies
react with red cells around the normal body temperature of 37°C (warm antibodies). Others are only active
at lower temperatures (cold antibodies) and do not usually cause clinical problems although they may be
picked up on laboratory testing.
Please note the Transfusion Handbook has not been updated since 2014 and requires review.
Guidance within the Handbook may therefore be out of date with other current guidelines.
Contact [email protected] for more information.
2.3: Testing for red cell antigens and antibodies in the laboratory
The ABO blood group system was the first to be discovered because anti-A and anti-B are mainly of the
IgM immunoglobulin class and cause visible agglutination of group A or B red cells in laboratory mixing
tests. Antibodies to ABO antigens are naturally occurring and are found in everyone after the first 3 months
of life. Many other blood group antibodies, such as those against the Rh antigens, are smaller IgG
molecules and do not directly cause agglutination of red cells. These ‘incomplete antibodies’ can be
detected by the antiglobulin test (Coombs’ test) using antibodies to human IgG, IgM or complement
components (‘antiglobulin’) raised in laboratory animals. The direct antiglobulin test (DAT) is used to detect
antibodies present on circulating red cells, as in autoimmune haemolytic anaemia or after mismatch blood
transfusion. Blood group antibodies in plasma are demonstrated by the indirect antiglobulin test (IAT).
Nearly all clinically significant red cell antibodies can be detected by an IAT antibody screen carried out at
37°C (see section 2.7).
page 2 of 7
Transfusion Handbook / 2: Basics of blood groups and antibodies
Please note the Transfusion Handbook has not been updated since 2014 and requires review.
Guidance within the Handbook may therefore be out of date with other current guidelines.
Contact [email protected] for more information.
2.4: The ABO system
There are four main blood groups: A, B, AB and O. All normal individuals have antibodies to the A or B
antigens that are not present on their own red cells (Table 2.1). The frequency of ABO groups varies in
different ethnic populations and this must be taken into account when recruiting representative blood donor
panels. For example, people of Asian origin have a higher frequency of group B than white Europeans.
Individuals of blood group O are sometimes known as universal donors as their red cells have no A or B
antigens. However, their plasma does contain anti-A and anti-B that, if present in high titre, has the potential
to haemolyse the red cells of certain non-group O recipients (see below).
Table 2.1 Distribution of ABO blood groups and antibodies
Blood group
Antigens on red cells
Antibodies in plasma
UK blood donors
O
none
anti-A and anti-B
47%
A
A
anti-B
42%
B
B
anti-A
8%
AB
A and B
none
3%
2.4.1: Transfusion reactions due to ABO incompatibility
ABO-incompatible red cell transfusion is often fatal and its prevention is the most important step in clinical
transfusion practice (Chapter 5). Anti-A and/or anti-B in the recipient’s plasma binds to the transfused cells
and activates the complement pathway, leading to destruction of the transfused red cells (intravascular
haemolysis) and the release of inflammatory cytokines that can cause shock, renal failure and disseminated
intravascular coagulation (DIC). The accidental transfusion of ABO-incompatible blood is now classified as
a ‘never event’ by the UK Departments of Health.
Transfusion of ABO-incompatible plasma containing anti-A or anti-B, usually from a group O donor, can
cause haemolysis of the recipient’s red cells, especially in neonates and small infants. Red cells stored in
saline, adenine, glucose and mannitol (SAG-M) additive solution (see Chapter 3) contain less than 20 mL of
residual plasma so the risk of haemolytic reactions is very low. Group O red cell components for intrauterine
transfusion, neonatal exchange transfusion or large-volume transfusion of infants are screened to exclude
those with high-titre anti-A or anti-B. Group O plasma-rich blood components such as fresh frozen plasma
(FFP) or platelet concentrates should not be given to patients of group A, B or AB if ABO-compatible
page 3 of 7
Transfusion Handbook / 2: Basics of blood groups and antibodies
components are readily available (Table 2.2). Cryoprecipitate contains very little immunoglobulin and has
never been reported to cause significant haemolysis. In view of the importance of making AB plasma readily
available, AB cryoprecipitate manufacture and availability is a low priority for the UK Blood Services.
Table 2.2 Choice of group of red cells, platelets, fresh frozen plasma (FFP) and cryoprecipitate
according to recipient’s ABO group
Patient’s ABO group
Red cells
Plateletsa
Fresh frozen plasma (FFP)b
Cryoprecipitate
O
O
O
O
A
A or B
A or B
O
First choice
Second choice
Third choice
AB
A
First choice
A
A
A
A
Second choice
Oc
Od
AB
O or B
Bd
Third choice
B
First choice
B
Ad
B
B
Second choice
Oc
Od
AB
O or A
Ad
Third choice
AB
First choice
AB
Ad
AB
AB
Second choice
A or B
Od
Ad
A or B
page 4 of 7
Transfusion Handbook / 2: Basics of blood groups and antibodies
Third choice
Oc
Bd
O
a Group B or AB platelets are not routinely available
b Group AB FFP is often in short supply
c Screening for high-titre anti-A and anti-B is not required if plasma-depleted group O red cells in SAG-M are used
d Tested and negative for high-titre anti-A and anti-B
Please note the Transfusion Handbook has not been updated since 2014 and requires review.
Guidance within the Handbook may therefore be out of date with other current guidelines.
Contact [email protected] for more information.
2.5: The Rh system
There are five main Rh antigens on red cells for which individuals can be positive or negative: C/c, D and E
/e. RhD is the most important in clinical practice. Around 85% of white Northern Europeans are RhD
positive, rising to virtually 100% of people of Chinese origin. Antibodies to RhD (anti-D) are only present in
RhD negative individuals who have been transfused with RhD positive red cells or in RhD negative women
who have been pregnant with an RhD positive baby. IgG anti-D antibodies can cause acute or delayed
haemolytic transfusion reactions when RhD positive red cells are transfused and may cause haemolytic
disease of the fetus and newborn (HDFN – see Chapter 9). It is important to avoid exposing RhD negative
girls and women of child-bearing potential to RhD positive red cell transfusions except in extreme
emergencies when no other group is immediately available.
Please note the Transfusion Handbook has not been updated since 2014 and requires review.
Guidance within the Handbook may therefore be out of date with other current guidelines.
Contact [email protected] for more information.
2.6: Other clinically important blood group systems
Alloantibodies to the Kidd (Jk) system are an important cause of delayed haemolytic transfusion reactions (
see Chapter 5). Kell (anti-K) alloantibodies can cause HDFN and it is important to avoid transfusing K
positive red cells to K negative girls and women of child-bearing potential. Before red cell transfusion, the
plasma of recipients is screened for clinically important red cell alloantibodies so that compatible blood can
be selected.
page 5 of 7
Transfusion Handbook / 2: Basics of blood groups and antibodies
Please note the Transfusion Handbook has not been updated since 2014 and requires review.
Guidance within the Handbook may therefore be out of date with other current guidelines.
Contact [email protected] for more information.
2.7: Compatibility procedures in the hospital transfusion laboratory
2.7.1: Group and screen
The patient’s pre-transfusion blood sample is tested to determine the ABO and RhD groups and the plasma
is screened for the presence of red cell alloantibodies capable of causing transfusion reactions. Antibody
screening is performed using a panel of red cells that contains examples of the clinically important blood
groups most often seen in practice. Blood units of a compatible ABO and Rh group, negative for any blood
group alloantibodies detected, can then be selected from the blood bank, taking into account any special
requirements on the transfusion request such as irradiated or cytomegalovirus (CMV) negative components.
Almost all hospital laboratories carry out blood grouping and antibody screening using automated analysers
with computer control of specimen identification and result allocation. This is much safer than traditional
manual techniques and eliminates most transcription and interpretation errors. ABO grouping is the single
most important test performed on pre-transfusion samples and the sensitivity and security of testing
systems must never be compromised. Robust identification procedures outside the laboratory at patient
blood sampling, collection of blood from the blood bank and administration of blood at the bedside are vital (
see Chapter 4). The current British Committee for Standards in Haematology (BCSH) guideline for pretransfusion compatibility procedures (2012) recommends that a second sample should be requested for
confirmation of the ABO group of a first-time transfused patient provided this does not impede the delivery
of urgent red cells or components (http://www.bcshguidelines.com).
2.7.2: Compatibility testing
Traditionally, the final step in providing safe blood is to carry out a serological crossmatch between the
patient’s plasma and a sample of red cells from the units of blood selected for transfusion. This is performed
by the IAT method at 37°C, looking for evidence of a reaction that would indicate incompatibility.
2.7.3: Electronic issue
This is sometimes known as computer crossmatching. Most hospitals now issue the majority of blood by
this safe and rapid technique. It relies on the fact that if the patient’s ABO and RhD groups are reliably
established, and a sensitive antibody screen is negative, the possibility of issuing incompatible blood is
negligible. The laboratory computer can identify all compatible units in the blood bank inventory without the
need for further testing. National guidelines require the use of automated testing systems interfaced with
laboratory information systems before electronic selection is used and all results must be transmitted
electronically to remove human error. Electronic issue should not be used:
If the patient’s plasma contains, or has been known to contain, red cell alloantibodies of clinical
significance
If the antibody screen is positive
If the patient has had an ABO-incompatible marrow or haemopoietic stem cell transplant
page 6 of 7
Transfusion Handbook / 2: Basics of blood groups and antibodies
If the patient has had an ABO-incompatible solid organ transplant in the last 3 months
For neonates or fetuses, if the mother has an IgG red cell antibody present in her plasma.
2.7.4: Blood for planned procedures
Many operations rarely need transfusion. As long as the laboratory can provide components quickly in an
emergency, there is no need to reserve blood units in the blood bank. Group and screen and electronic
issue are now widely used in this situation and allow more efficient use of blood stocks and laboratory
scientist time.
Patients undergoing planned procedures that may require transfusion, such as major surgery, ideally have
samples for group and screen taken at preadmission clinics. Problems in providing compatible blood are
then identified before admission to hospital. There is a (usually small) risk that the patient may develop new
blood group alloantibodies between the time of initial testing and the date of operation, especially if they
have recently been transfused or become pregnant. Having reviewed current evidence, the BCSH
guidelines for pre-transfusion compatibility procedures (Milkins et al., 2012) made the following pragmatic
recommendations for timing of pre-transfusion blood samples:
Testing should be performed on samples collected no more than 3 days in advance of the
transfusion when the patient has been transfused or become pregnant within the preceding 3
months.
An extension to 7 days may be considered for regularly/frequently transfused patients with no
alloantibodies and pregnant women with no significant alloantibodies who need to have blood
standing by for a potential obstetric emergency such as placenta praevia.
Remote issue of compatible blood components from satellite blood refrigerators electronically linked to the
laboratory computer system allows safe and efficient provision of blood when the transfusion laboratory and
operating theatres are on different hospital sites. Successful adoption of this approach requires close
collaboration with the clinical team and clear local guidelines and policies.
When electronic issue is not available or appropriate and in procedures with a high probability of requiring
transfusion a maximum surgical blood ordering schedule (MSBOS) should be agreed between the surgical
team and transfusion laboratory. This specifies how many blood units will be routinely reserved (in the blood
bank or satellite refrigerator) for standard procedures, based on audits of local practice. When developing
an MSBOS it is usual to aim for a crossmatched to transfused ratio of no more than 3:1 and actual blood
use should be audited and reviewed at regular intervals.
page 7 of 7
Purchase answer to see full
attachment
