Investigating weak A subgroups in a healthy lady: The blood bank limitations.

Sir,

Weak A subgroups such as A3, Ax, Aend, Am, Ay, and Ael are often mistyped as group O and may be potentially dangerous with regards to whole blood transfusion. These subgroups can be serologically differentiated using recommended techniques.[12] Special tests like serum glycosyltransferase estimation and genotyping are performed in advanced laboratories to confirm these blood groups.[34]

We observed a discrepancy between the routine forward and reverse blood grouping of a 45-year old healthy lady. The forward group revealed ‘O’ positive and reverse showed ‘A’ group. No clerical errors and reagent problems were observed. We performed a detailed serological investigation on the lady's red cells with both tube technique and Gel method (DiaMed, Cressier s/Morat, Switzerland) [Table 1]. Since the red cells showed no agglutination with either Anti-A and Anti-AB, we suspected a possible Am or Ay or Ael phenotype. The red cells were then subjected to adsorption – elution tests using human polyclonal Anti-A as described elsewhere.[2] To our surprise the eluate reacted with the reagent ‘A’ cells indicating the presence of ‘A’ antigen on the test red cells. The result was then validated with a) the eluate showing agglutination with two different reagent ‘A’ cells at all phases b) eluate failing to agglutinate reagent ‘O’ cells and c) the final wash solution failing to agglutinate with all the four reagent red cells ‘A’, ‘B’, ‘AB’ and ‘O’[2] [Table 2]. Blood groups of her husband and one son who were available then were confirmed to be ‘O’ positive. Saliva study showed that the lady was a secretor and carried both ‘A’ and ‘H’ substances thus excluding the probability of Ael phenotype. Serologically ‘Ay’ is almost similar to ‘Am’ and even adsorption – elution test fails to differentiate the two phenotypes. In the present study Anti-A eluted from the lady's red cells reacted weakly with the corresponding reagent ‘A’ cells (Agglutination strength: 1+ by tube technique and 2+ by Gel) which is in favor of ‘Ay’ phenotype. In case of ‘Am’ phenotype such agglutination strength is significantly stronger.[1] Finally we reported the patient as “Weak A subgroup” Rh positive.

Table 1

Test on red cells and serum

Table 2

Adsorption-elution test

We advised both serum glycosyltransferase estimation and genotyping of the lady for confirmation of her weak ‘A’ subgroup. We were really in a dilemma as to how the reporting should be done in the present case. We were not sure whether designating the lady as “Weak A subgroup” Rh positive was a proper reporting format. Since confirmatory tests for weak ‘A’ phenotype is beyond the scope of most blood banks, there should be a system to report these weak ‘A’ individuals.