Blood groups and Anti-D in pregnancy

• Antibodies are immunoglobulins (Globular proteins with immune functions). They bind to receptors called antigens in a lock and key fashion. They may alert other cells to targets with foreign antigens, they may also directly cause dysfunction, destroy the cell or cause agglutination (clumping).
• ABO +ve/-ve system

  • default state is having immunoglobulins to all these antigens (A, B and Rhesus)
  • if you have a positive antigen (A, B, both AB or Rh) you must not have the immunoglobulin
  • The body has made an allowance for these antigens to exist without reacting to them
• For blood transfusion

  • test patients blood group, what antigens do they have?
  • These are the antigens they will tolerate, you cannot give them alternative antigens, but you can give the blood without antigens (O and Rh negative)
  • Therefore those with AB positive blood, tolerate all antigens and are universal acceptors
  • Those who are O negative (no AB antigens and no Rhesus antigen) are universal donors
• Effects of incompatible blood transfusion

  • antibody-antigen reaction (agglutination)
  • activates plasma proteins of complement family
  • Plasma membrane of RBC leaky
  • clumps form blockages in vessels and clots
  • acute kidney injury, blocked nephrons by haem
  • haemolysis of RBC and release of haemoglobin and toxins into circulation
• Testing for antigens

  • add a sample of patient’s blood to solutions containing immunoglobulins
  • can see if the blood agglutinates or stays in solution
  • clumping suggests that the antigen complimentary to the immunoglobulin is present
• Blood typing - single drops of blood are mixed with different antibodies, if agglutination occurs it corresponds to the antigen in the red blood cell.
• Blood Crossmatching - donor blood selected which is ABO compatible. donor and recipient blood mixed. If no agglutination - compatible.
• Haemolytic disease of the newborn - if a small amount of Rh+ fetal blood leaks from the foetus through the placenta into the bloodstream of the Rh- mother, mother will make anti-Rh antibodies. Blood mixing happens at birth, so does not affect first pregnancy.

  In subsequent pregnancies if foetus is Rh+ agglutination and haemolysis of fetal blood occurs as anti-Rh antibodies can cross placenta.

  Anti-Rhesus Gamma Globulin is given to Rh- mothers close after delivery, miscarriage or abortion. Works by binding and inactivating Rh antigens before the mothers immune system can
• • A mother who has no Rhesus antigens may give birth to a newborn who does have Rhesus antigens (e.g. from a Rhesus positive father)
  • the mother's antibodies may attack the newborn's RBC and cause severe haemolysis, ranging from anaemia to fatal hydrops fetalis
  • does not affect the first born (unless invasive procedure) as mother does not detect baby's blood until birth but subsequent children will be affected
  • we give Rhesus immunoglobulin (anti-D) to mothers before and after birth intramuscularly - this competitively blocks the Rhesus antigen, keeping them undetected by maternal antibodies
• A type blood has A cell surface proteins on its red blood cells and anti-B proteins in plasma. It is compatible with O and A blood types.
• B type blood has B cell surface proteins, and anti-A proteins in plasma. It is compatible with O and B blood.
• AB blood has A and B cell surface proteins and no proteins in plasma. It is compatible with all ABO blood types.
• o blood has no cell surface proteins, and anti-A and anti-B proteins in plasma. It is only compatible with O type blood.
• Direct Coombs test

  • blood sample from a patient with immune mediated haemolytic anaemia
  • the patient's washed RBCs are incubated with antihuman antibodies (Coombs reagent)
  • RBCs agglutinate: antihuman antibodies form links between RBCs by binding to the human antibodies on the RBCs
• Indirect Coombs test

  • recipient's serum is obtained, containing antibodies
  • donor's blood sample is added to the tube with serum
  • recipient's antibodies that target the donor's red blood ells form antibody-antigen complexes
  • anti-human antibodies (Coombs antibodies) are added to the solution
  • agglutination of red blood cells occurs, because human antibodies are attached to red blood cells
• Blood typing is a method of classifying blood into different blood groups depending on the presence of different antigens on the surface of red blood cells (RBCs). Understanding the different blood groups is vital in preventing complications from blood transfusion.
• Erythrocytes (RBCs) have multiple glycoprotein antigens attached to their cell surface. The most important are ABO antigens, which determine a person's ABO blood group. An individual inherits one ABO allele from each parent, with A and B alleles being codominant and producing the A and B antigens respectively.
• Group A - have antigen A attached to the erythrocyte cell surface

  Group B - have antigen B attached to the erythrocyte cell surface

  Group AB - have both antigen A and B attached to the erythrocyte cell surface

  Group O - have neither antigen attached to the erythrocyte cell surface
• Each person also has ABO antibodies in their plasma, which will recognise and attack RBCs expressing foreign antigens. These antibodies develop over the first months and years of life. This is crucial in blood transfusion as giving someone an incompatible blood group can be potentially fatal. The A and B antibodies are predominantly IgM.
• Group A - have anti-B antibodies

  Group B - have anti-A antibodies

  Group AB - have neither antibody

  Group O - have both anti-A and anti-B antibodies
• The second most important blood grouping system is based on Rhesus (Rh) antigens. There are many different Rh antigens but only 5 are clinically significant: D, C, c, E and e.

  RhD is the most immunogenic (i.e. likely to produce an immune response) and therefore the most likely to precipitate a transfusion reaction. The presence or absence of Rh D antigen on the erythrocyte cell surface determines whether the person has Rh positive (Rh+) or Rh negative (Rh-) blood groups.
• Rh positive: have the Rh D antigen and can receive both Rh+ and Rh- blood

  Rh negative: lack the Rh D antigen and should only receive Rh- blood
• Rh negativity is generally more prevalent in Caucasian populations (15%) than Afro-Caribbean (8%) and Asian (1%) populations but prevalence varies in different parts of the world.
• Anti-D antibody is usually absent in Rh- patients (until they have been exposed to Rh+ erythrocytes). Rh- patients should not be transfused with Rh+ blood as this can cause them to develop anti-D antibodies. This may cause transfusion reactions in the future.
• Alongside ABO and Rh blood groups, there are many other grouping systems based on other antigens. These antigens can also, more rarely, cause transfusion reactions.
• A person should not receive blood products containing antigens for which they have the corresponding antibodies. Transfusing an incompatible blood type will precipitate a potentially fatal transfusion reaction as the recipient's ABO antibodies attack the donor's antigen (seen as foreign). Patients having blood transfusions need to be frequently monitored, particularly at the start of each unit.
• People with blood type O- are universal donors - they can donate their blood to anyone. This is because their RBCs have no A, B or RhD antigens which the recipient's immune system could attack.
• People with blood type AB+ are universal recipients - they can receive blood from anyone. This is because their plasma does not contain anti-A, anti-B or anti-D antibodies, so they will usually not mount an immune response to the donor blood.
• Anti-D antibodies cause the most severe type of haemolytic disease of the newborn.
• Exposure of a Rh- person to the RhD antigen causes RhD sensitisation. For instance, during a first pregnancy if the foetus is Rh+. The presence of RhD antigens in the maternal circulation stimulates the production of anti-D antibodies.
• Maternal anti-D antibodies recognise and destroy foetal Rh+ RBCs. Upon first exposure, the antibodies are IgM which cannot cross the placenta and will not cause issues in the first pregnancy. However, future Rh+ pregnancies will result in the production of large amounts of IgG anti-D which can cross the placenta and cause haemolysis.
• The administration of anti-D Ig prophylaxis to unsensitised Rh- mothers has significantly reduced the incidence of HDN caused by anti-D antibodies. The prophylaxis works by destroying foetal RBCs that leak into the maternal circulation, reducing the chance of Rh D sensitisation.
• Blood typing (also known as a group and save) followed by cross-matching helps avoid transfusion of incompatible blood types. ABO typing tests the patient's blood for the presence of A/B antigens, and A/B antibodies. This is followed by Rh typing. The lab will also screen the patient's blood for atypical antibodies. Cross-matching involves mixing the donor's blood with the recipient's blood to detect any immune reaction.
• Direct Antiglobulin testing detects whether a patient's RBCs have antibodies directly attached to them. Coombs' reagent binds to specific immunoglobulins on the RBCs. It is added to the patient's blood. A positive test results in the RBCs agglutinating (clumping together). A positive DAT indicates that haemolysis has an immune aetiology, causes include autoimmune haemolytic anaemia, haemolytic transfusion reactions, and HDN.
• Indirect Antiglobulin testing detects antibodies present in the patient's plasma. This can be used in cross-matching or to detect maternal anti-D IgG. Donor's RBCs and Coombs' reagent is combined with the patient's isolated plasma. The test is positive if agglutination occurs. This indicates the patient has antibodies against the antigens present on the donor's RBCs.