Other Subgroups

A3

The A3 subgroup is a fairly rare subgroup (1/1000). Macroscopic reactions may range from negative, to w+, to 1+, to 2+. Microscopically, mixed-field agglutination (MFA) is present.

The main distinguishing feature of A3 red cells is MFA with anti-A and anti-A,B.

Ax(Ao)

This is a very rare subgroup (1/40,000).

The main distinguishing features of Ax cells are:

  1. the A antigen is so weak it may only be detectable by using anti-A,B; and
  2. anti-A1 is usually present in the serum. If anti-A,B is not used, Ao cells may be mistyped as group O.

Am

This is a very rare subgroup.

The main distinguishing features of Am cells are:

  1. no reaction with anti-A or anti-A,B in routine testing, and
  2. anti-A1 is not present in the serum.

NOTE: Many more subgroups of A exist, such as A4, Abantu and Afinn.

Table 4-4. Rare subgroups of A.

Group anti-A,B anti-A anit-B A1 cells B cells
A3 1+* 1+* -- -- 4+
Ax(Ao) 1+* --/w+ -- 2+ 4+
Am --** --* -- -- 4+
* Macroscopic reactions typically range from negative to w+ to 1+.
** The red cells usually do not react with anti-A or anti-A,B but are capable of absorbing and eluting anti-A.

B subgroups: These exist but are very rare.

Other Subgroups

©1999 Division of Medical Laboratory Science
University of Alberta