ABO Blood Groups
ABO Blood Groups. ABO blood groups are assigned based on the major blood group antigens present on a patient’s red cell. Patients can either have A, B, A and B or no antigens (blood group O). Patients have naturally-occuring antibodies to the antigens they lack; i.e., blood group A patients have anti-B antibodies, blood group B have anti-A antibodies, blood group AB have no antibodies and blood goup O has anti-A and anti-B antibodies. This has implications for blood transfusion, as anti-A and anti-B are IgM antibodies active at body temperature which directly agglutinate cells and fix complement, resulting in immediate complement-mediated haemolysis. Because a patient’s cells express antigens and their plasma contains antibodies, they must only receive blood products from specific groups of people. Note that the terms “universal donor”, which is usually applied to blood group O, and “universal recipient”, which is usually applied to blood group AB, is only true for the transfusion of red cells. Plasma products may contain donor A or B antibodies capable of reacting with recipient red cells; hence, the same compatibility rules do not apply as packed red cells.
  • ABO grouping is the single most important serological test performed on pre-transfusion samples, and the sensitivity and security of the testing system must never be compromised.
  • SHOT data has demonstrated that the majority of ABO errors arise from manual systems. Hence, the process should be fully automated insofar as possible. 
  • This reduces the risk of transcription and interpretation errors.
  • Full ABO grouping should include a forward and a reverse group.
    • Full groups must be performed on all first-time groups.
    • An exception to this is neonates, where the reverse groups are unhelpful due to the antibodies likely being maternal in origin.
      • In such cases, the forward group should be done twice.
    • Subsequent samples may omit the reverse group, but only after a full risk assessment, taking into account that the first sample may be from the wrong patient (risk of 1 in 2000).
    • If a reverse group is omitted:
      • No manual editing of results is permitted.
      • The forward group must match historical records.
      • There must be at least one historical record which contains both a forward and reverse group.
        • This must have been performed i n a fully-automated system.
  • Reverse grouping has several advantages:
    • It acts as a built-in check of the forward group.
    • It can highlight anomalies following ABO incompatible stem cell transplantation.
    • It may highlight anomalies following transfusion.
    • It may help  demonstrate cold agglutinins. 
  • Reagents:
    • Certain commercial reagents contain potentiators such as polyethylene glycol (PEG), which can cause false positives, especially when RBCs  are coated with in vivo immunoglobulin. Laboratories using such reagents should have policies in place to reduce the risk of misinterpretation (e.g. inclusion of a diluent control).
    • The anti-B reagent should not react with an acquired B antigen. 
  • Interpretation:
    • Manual intervention may be necessary in automated systems, but this should be auditable.
    • Original reaction patters should be stored and always accessible.
    • All reactions must be visually inspected (reviewing computer images is insufficient as mixed field reactions may be missed) prior to decisions being made.
    • For manual systems, the risk of error can be minimised by separating the procedure into distinct tasks, and using different members of staff for each task.
  • Prior to testing and prior to result release, patient demographics on the sample must be checked against the system, to ensure they match and that no errors have been made during data entry into the LIMS.
  • The ABO and RhD type must be verified against historical records. 
    • If there is a discrepancy, a further sample must be obtained and tested immediately.
    • If transfusion is urgently required in the meantime, group O blood must be given.

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