ABO Group Type

ABO antigens are primarily glycolipids found on the surface of human red blood cells as well as in various body tissues. ABO grouping consists of two components:

1. Direct (Forward) Grouping:
   Uses known anti-A and anti-B typing antisera to test unknown red blood cells. Agglutination indicates the presence of the corresponding antigen (A, B, or both). Lack of agglutination with both antisera indicates group O.
2. Indirect (Reverse or Back) Grouping:
   Uses a pool of known group A and B cells. Agglutination occurs when antibodies in the patient’s serum react with corresponding antigens on reagent red blood cells.

– Anti-A or anti-B in patient serum will agglutinate cells with A and/or B antigens.
– Group O red blood cells should show no reaction with patient serum.

Both forward and reverse typing is routinely performed to confirm accuracy.

Approximate ABO frequencies in a Caucasian population:
• A – 41%
• B – 9%
• AB – 4%
• O – 46%

Tubes containing serum separator gel (may cause false agglutination; will be rejected)

None required

Reported as blood group A, B, AB, or O.

• American Association of Blood Banks. Technical Manual, 9th ed. Arlington, VA: AABB; 1985.

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