Blood transfusions

• Describe the red cell antigens

  Surface antigens on RBCs are composed of glycoproteins or glycolipids. There are approximately 400 red cell group antigens, with the most clinically relevant groups being ABO and Rh.
• Describe the ABO system

  Blood group A: RBCs contain A antigens on their surface and anti-B antibodies in their plasma

  Blood group B: RBCs contain B antigens on their surface and anti-A antibodies in their plasma

  Blood group AB: RBCs contain A and B antigens on their surface and no anti-A or anti-B antibodies in their plasma

  Blood group O: contain no A or B antigens on their surface and have both anti-A and anti-B antibodies in their plasma
• Describe the genetics underlying the ABO system

  • Genes encoding the ABO antigens are present on chromosome 9
  • Autosomal dominant inheritance, with Co-dominance between the A and B alleles.
  • ABO system consists of three alleles genes; A, B and O
  • O is recessive
• Describe ABO antigens

  The ABO genes produce specific glycosyltransferases, which add sugars to a basic precursor substance, such as a glycolipid and glycoprotein, to produce H substance. These ABO genes control the synthesis of enzymes that are responsible for the addition of single carbohydrate residues. The O gene has no effect on H substance, N-acetyl galactosamine is added for group A and D-galactose is added for group B.
• How does the body develop Anti-A or Anti-B antibodies?

  Following birth, these antibodies develop due to interactions with the environment, for example specific sugars that mimic these antigens on the surface Of RBCs.
• Describe the different subtypes of blood group A

  Blood group A can be split into two different subtypes; A1 and A2. A1 accounts for around 80% of antigens, whereas A2 accounts for the remaining 20%.
• What is the Bombay phenotype?

  These is an extremely rare blood group variant, which is incapable of forming 2-L-fucosyltransferase necessary for formation of H substance. Therefore, RBCs lack expression of H substance and their plasma contains antibodies to H substance as well as A and B antigens. Individuals with this phenotype can only be transfused with blood from other Bombay phenotype individuals.
• Describe the universal donor and recipient

  • Blood group O is the universal donor (Rh -ve)
  • However, group O people have anti-A and anti-B in their plasma, so cannot be universal donors for blood plasma; instead this is group AB
  • Blood group AB are universal recipients as they do not have any anti-A or anti-B antibodies.
• Describe the Rh blood group system 


  There is up to 49 antigens in the Rh blood group system, but this consist of only 5 main antigens; C, c, D, E and e. D has the largest clinical influence. Two genes exist; RhD and RhCE. The RhD gene encodes protein with the D antigen and the RhCE gene encodes the RhCE protein with the C, c, E and e antigens.
• Describe inheritance in the Rh blood groups

  The RhD gene has two alleles:

  • Rh+, encodes the D antigen- dominant
  • Rh-, does not encode the D antigen- recessive

  ABO and Rhesus genes are not linked and are inherited independently.
• What is the R0 subtype?

  This refers to when the RHD and RHCE genes combine to produce 'Dce'. If someone has this subtype, then they have to have the RHD gene and thereby a positive blood group. This also means that people with the R0 subtype always have to have Rh+ blood.
• Why are blood group subtypes important?

  Some medical conditions require multiple blood transfusions, so these patients need to be given more extensively matched blood, usually the same subtype. For example, people with sickle cell anaemia may require multiple transfusions.
• Describe the frequency of the R0 subtype

  • 3% of the regular blood donors in England have the R0 subtype
  • Demand for this subtype is increasing by 10-15% each year
  • The R0 subtype is more than 10 times as common in individuals from Black African or Black Caribbean and mixed heritage backgrounds
• Describe haemolytic disease of the newborn

  This disease can occur in Rh- mothers carrying Rh+ foetuses.

  1. During the first pregnancy, Rh antigens enter the mother's circulation through breaks in the placenta.
  2. The mother then produces anti-Rh antibodies in response
  3. During the second pregnancy, the mother's anti-Rh antibodies cross the placenta and destroy foetal blood cells.
• How is haemolytic disease of the newborn prevented?

  All pregnant women are tested for their blood type. Then all pregnant women can be given anti-D immunoglobulin at various points during pregnancy and after birth to "mop up" and destroy Rh D positive foetal cells before they can sensitise the immune system of the mother to produce its own anti-D.
• Describe the method of blood transfusion

  Blood is collected from a donor by aseptic technique into plastic bags that contain an anticoagulant. Prior to use ABO and Rh status are determined. The collected blood is processed and separated into components before use. The blood bags are then stored in store units in hospitals.
• Describe the storage of red cells

  • One unit: 280ml. (leukodepleted=WBCs removed)
  • Each unit of red cells increases the Hb by approx. 10g/L
  • Stored at around 4 degrees C
  • Shelf-life: up to 35 days
  • Each bag contains a side tube which allows you to take a sample without opening the blood bag
• Describe fresh frozen plasma (FFP)

  • One unit: 200-250ml
  • Prepared from anticoagulated whole blood by separating and freezing to -30 degree C within 6 hours of collection
  • Contains all coagulation factors
  • Group specific
  • Shelf-life: up to 36 months frozen and 24 hours at 4 degrees C after thawing
• Describe platelet transfusions

  • One adult dose of platelets is pooled from 4 different platelet donations
  • Expected to increase platelet count by 20-49 x 10^9
  • Shelf-life: 5 days
• Describe ABO forward and reverse grouping

  Forward grouping: adding patient's red cells to tubes containing antibodies to detect coagulation

  Reverse grouping: adding patient's red cells to tubes containing antigens to detect coagulation