ABO Discrepancies

ABO Discrepancies:
An important part of blood banking is knowing how to deal with unexpected results. Discrepancies in the blood bank are common and knowing how to solve them is critical. They can be caused by patient RBCs, patient serum, an underlying condition, human error, or a number of factors. Blood cannot be released if there is an unresolved discrepancy. Here are a few common discrepancies to be aware of.

1. Patient has A2 RBCs and anti-A1
     a. Remember not all people with A2 blood make anti-A1, in fact most don’t. The ones that do make anti-A1 will usually have a 1+ or 2+ reaction (weak reaction) in the reverse typing to A1 cells. The forward typing will usually be 4+ for anti-A, unless they are A2B in which case the forward typing may be 3+ with anti-A because the B antigens can slightly interfere with the reaction. (A patient with a cold autoantibody or alloantibody could have similar typing results so pay attention to all results and patient symptoms.) A patient with a cold autoantibody will have a positive autocontrol, whereas a patient with A2 RBCs and anti-A1 will have a negative autocontrol.

2. Rouleaux
     a. Rouleaux causes RBCs to stick together causing a false agglutination. This can be resolved by using a saline dilution. 2+ results in the forward typing (unexpected antibodies) is an indicator.

3. Acquired B antigen
     a. Patients with acquired B antigen will have results typical of a patient with A type blood but will also have a 1+ or 2+ reaction in the forward typing with anti-B. This can be caused by a type of gastrointestinal disease where bacteria change the A antigen sugar to appear like B antigen. The reagent anti-B weakly binds this creating a discrepancy.

4. Zeroes across the board
     a. Some blood type O individuals are unable to produce a sufficient amount of antibodies for the reverse type reaction. This can be due to old age, infancy, or immunodeficiency.

5. Cold alloantibody or autoantibody in patient serum
     a. A strong forward typing and a weak reverse typing is indicative of a cold allo or auto antibody in the patient serum. This can be resolved by warming the serum before repeating the reverse typing. Reagent A1 and B cells that are negative for the detected antibody could also be used to get a correct typing.

6. Mixed field
     a. A mixed field in the forward typing can be indicative of a blood transfusion. For example if you have a mixed field of 4+ and 0 in the forward typing, this could be due to a patient with A, B, or AB blood receiving O donor blood.