In routine practice, specially prepared blood grouping sera containing anti-A, anti-B, (and optionally anti-A,B) are used to identify the four types of red cells (see Table 2). These sera will agglutinate cells with the corresponding antigen. This is called forward typing.
Table 2. Testing the Patient Red Cells with Known Antisera (Forward Typing).| ABO Blood Group | Patient Red Cells Tested with Known Antisera |
| Anti-A | Anti-B | Anti-A,B |
A | 3–4+ | 0 | 3–4+ |
B | 0 | 3–4+ | 3–4+ |
O | 0 | 0 | 0 |
AB | 3–4+ | 3–4+ | 3–4+ |
+ = agglutination (graded 1+ to 4+); 0 = no agglutination
