ABO blood grouping and transfusion compatibility

Erythrocyte antigens have been explored this in the following SAQs:

  • Question 1  from the second paper of 2012 (“false chimerism”)
  • Question 24.1 from the second paper of 2010 (mismatched transfusion)
  • Question 24.2 from the second paper of 2010 (“Which of these blood products require a crossmatch?”)

The ABO grouping seems to be the most important, followed by rhesus status.

In case one needs to revise what these mean, the Australian Red Cross has some decent materials on the topic. Additionally, some local notes from the CICM First Part Exam section could be of interest.  In short, the grouping refers to which antigens your RBCs possess. Group A people have RBCs covered in type A antigens, and possess anti-B antibodies. Group O have both anti-A and anti-B antibodies, and group AB have no antibodies. And so forth. Its not rocket science. However, if you have serious problems remembering these things, here it is again:

  • Everyone can receive O blood (the cells have no agglutinins on them).
  • O people can have O blood only (they have antibodies to both A and B agglutinins)
  • A people can get A or O blood only (they have anti-B agglutinins)
  • B people can get B or O nlood only (they have anti-A agglutinins)
  • AB people can receive any blood: they have no anti-aggutinin antibodies, but their AB cells are covered in agglutinins.
  • Nobody other than other AB people can receive AB blood (as it is covered in A and B agglutinins)

Which products need a crossmatch?

The CICM examiners love to ask this question. One can reason though it logically. What causes reactions to the transfusion of blood products? It is the binding of antibodies to antigens on the red cell surface. Thus it is probably quite safe to receive plasma, or any cells that dont have ABO antigen molecules on their surface. The table below illustrates this concept, and is repeated several times in the CICM fellowship exam.

Blood Product

Need for Crossmatch

Packed red blood cells




Fresh Frozen Plasma




Prothrombin concentrate


Granulocyte concentrate


Intravenous immunoglobulin


The use of uncrossmatched blood

Type O uncrossmatched blood generally seems safe enough to use when needed.

It is also possible to give Rhesus-positive blood to a rhesus-negative person, as a gesture of desperation.

Adverse events associated with blood transfusion

In general, the adverse events associated with blood transfusion are diminishing in incidence, but one should know what they are:

  • ABO-incompatible blood transfusion (due to administrative error)
  • Bacterial contamination of platelet components (1:2,000)
  • Sepsis from bacterial contamination of red cell components(1:500,000)
  • HIV infection ( 1:2,135,000)
  • Hep C infection (1:1,935,000)
  • Hep B infection (1:205,000)
  • Human T-lymphocytic viruses (1:2,993,000)
  • Transfusion-related acute lung injury (TRALI)
  • Fluid overload and heart failure
  • Dilutional coagulopathy

Mixed-field agglutination

Attempts at ABO blood grouping following a transfusion of uncrossmatched blood causes "Mixed-field RBC agglutination", which is a case of "false chimerism". This is a situation where there are two very different blood cell populations, confusing the automated testing apparatus. It may take longer for the technicians to identify some safely transfuseable crossmatched blood after receiving a specimen like that. On top of this, sensitization can occur, leading to hemolytic reactions. The chances of this happening are around 0.4%.


SCHWAB, C. WILLIAM, JOHN P. SHAYNE, and JOHN TURNER. "Immediate trauma resuscitation with type O uncrossmatched blood: a two-year prospective experience." Journal of Trauma and Acute Care Surgery 26.10 (1986): 897-902.

Busch, Michael P., Steven H. Kleinman, and George J. Nemo. "Current and emerging infectious risks of blood transfusions." Jama 289.8 (2003): 959-962.

Sandler, S. G., H. Yu, and N. Rassai. "Risks of blood transfusion and their prevention." Clinical advances in hematology & oncology: H&O 1.5 (2003): 307-313.

Bluth, Martin H., Marion E. Reid, and Noga Manny. "Chimerism in the immunohematology laboratory in the molecular biology era." Transfusion medicine reviews 21.2 (2007): 134-146.

Goodell, Pamela P., et al. "Risk of hemolytic transfusion reactions following emergency-release RBC transfusion." American journal of clinical pathology134.2 (2010): 202-206.