A call to implement both the forward and reverse ABO typing for pre-transfusion testing in sub-Saharan Africa

The weak expression of A and B antigens on the RBC surface give rise to weak sub-groups/phenotypes of A and B. This is a common cause of ABO forward & reverse typing discrepancies. Examples of weak sub-groups in the group A are; A1, A2 A3, Ax, Ael and Am. These are more common than the B-subtypes, which include; B1, B2, B3, B4, Bv, Bw, Bx, Bm, Bh, Bint and Bel. In the literature, the terminologies and nomenclature of these weak subgroups can be diverse and sometimes confusing, but in general, they are based on serological reactions [1-3].

The subgroups of A are not rare in SSA, as Cserti-Gazdewich et al, has shown in a cohort of 1933 children, who were 45.8% group O, 26.8% group A (518/1933), 22.2% group B, and 5.2% (101/1933) group AB. Using anti-A1 Lectin antisera, expression of A1 in 497/619 of the A and AB individuals was determined. The authors found that 91.1% were A1 positives (A1 or A1B), while 8.9% (44/497) were A1 negative [4]. The latter represent the other weak-A sub-types such as A2 and A3. These individuals, especially A2, can make alloanti-A1 which can cause ABO typing discrepancies and incompatible crossmatches. In the setting where reverse typing is not performed, these may go undetected and can cause hemolytic transfusion reactions. In other settings, weak ABO subtypes and alloanti-A1 antibody are responsible for 25·4% and 2·2% of ABO typing discrepancies in patients [5].

Commercial A1- and B-cells to perform reverse typing are available in most parts of SSA. Alternatively, these A1-cells and B-cells can also be prepared in-house by making pools of known A-cells and B-cells from the national blood centers – making it cost effective.

Performing both the forward and reverse typing during pretransfusion testing should therefore be the recommended practice in SSA. This may not require special skills, yet will help mitigate hemolytic transfusion reaction risks.