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Resolution of blood group discrepancy and serological evaluation of weak B phenotype in a healthy blood donor: A case report from West Bengal

 Department of Transfusion Medicine and Blood Centre, Peerless Hospital, Kolkata, West Bengal, India

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Date of Submission11-Feb-2021
Date of Decision07-Apr-2021
Date of Acceptance02-May-2021
Date of Web Publication04-Jun-2022


Several weaker subgroups of B have been described (e.g. B3, Bx, Bm, and Bel) which are very infrequently encountered. These subgroups show weaker and variable serologic reactivity with the commonly used human polyclonal antisera, thus causing group discrepancy and dilemma to resolve these problems and mismatch blood transfusion. Here, we present a case of weak B subgroup detected in a 40-year-old male voluntary blood donor. His red cells showed weak agglutination with anti-B and anti-AB, and in his serum, there were potent anti-A and weak anti-B which were not detected at 37°C. After adsorption with anti-B, an eluate was prepared from the patient's cells which agglutinate with B and AB cells but did not agglutinate with A or O cells. His probable blood group is Bx . With special serological testing, a rare group is detected and decision is made to provide blood to the right patient at the right time.

Keywords: Adsorption–elution, group discrepancy, weak B

How to cite this URL:
Mukherjee S, Dastidar AG, Kumar V, Chatterjee P. Resolution of blood group discrepancy and serological evaluation of weak B phenotype in a healthy blood donor: A case report from West Bengal. Asian J Transfus Sci [Epub ahead of print] [cited 2023 Mar 24]. Available from:

   Introduction Top

The ABO system is the most important of all blood groups in transfusion practice. It is the only blood group system in which individuals have antibodies in their serum to antigens that are absent from their red blood cells (RBCs). Transfusion of ABO-incompatible blood can be associated with acute intravascular hemolysis and renal failure, and can be fatal. ABO antigens are found in substantial amount on red cells and platelets, body fluids in secretors, and many other tissues.[1]

ABO subgroups are phenotypes that differ in the amount of A and B antigens carried on red cells and present in secretions. Variable erythrocyte antigenic expressions (qualitative and/or quantitative difference) owing to allelic heterogeneity, give rise to subgroups. Multiple weak B subgroups (e.g. B3, Bx, Bm, and Bel) have been described.[2] Subgroups of “B” with decreased expression of the B antigen are of very rare occurrence in the general population as very few cases have been reported before. It was usually recognized by apparent discrepancies between red cell (forward) and serum (reverse) grouping. It is important to detect and resolve discrepant ABO grouping results so as to prevent ABO mismatch transfusions. Such individuals should also be informed of their respective blood donor and transfusion recipient status, as well.

Here, we present a case of subtype B, serological characteristics similar to Bx blood type and steps of resoluting group discrepancy problem.

   Case Report Top

A 40-year-old male donated at our center as a voluntary blood donor. He is a first-time donor and known to be O-positive blood group. Three hundred and fifty milliliters of blood was collected in triple blood bag, and the sample was taken in ethylenediaminetetraacetic acid vial for blood grouping. Initial blood grouping was done in DiaMed-ID typing gel card (Bio-Rad, Cressier, Switzerland). The following result was noted at room temperature [Figure 1].
Figure 1: Group discrepancy in DiaMed ID typing gel card (Bio Rad, Cressier, Switzerland)

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Initial interpretation

  • Forward grouping: O Rh D positive
  • Reverse grouping: B Reaction with anti-H: 4+.

Repeat testing was done by conventional tube technique method at room temperature, 4°C, and 37°C. At 4°C, mild transient reaction with B cells shown in reverse grouping which confirms the presence of weak B in the donor's serum. The results are given in [Table 1].
Table 1: Antigens and antibodies found in the patient's sample

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Since these results were inconclusive, further tests were done.

Cold adsorption and heat elution techniques were performed for confirmation of blood group.[3],[4] The presence of A antigen or B antigen or both requires adsorbing anti-A or anti-B to the red cells, followed by elution of bound antibody. The eluate is then evaluated for the presence of anti-A or anti-B by testing against A1 or B reagent red cells.

Cold adsorption

One milliliter of the patient's red cell was mixed with 1 ml of anti-B (human polyclonal) and incubated at 4°C for 1 h. The cells were washed with cold normal saline for eight times and the final wash was preserved.

Heat elution

Equal volume of washed red cell and 6% bovine albumin was mixed and placed at 56°C for 10 min. After centrifugation, the eluate was transferred into a fresh tube.

Both the final wash and eluate were tested against three different O cells and three B cells. The results are shown in [Table 2].
Table 2: Result of cold adsorption and heat elution

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The results indicate the presence of anti-B in the eluate, thereby demonstrating the presence of B antigen on the surface of the patient's blood cells. During crossmatching with B-positive donors, the sample shows compatibility at 37°C. Direct Coombs test and indirect Coombs test on the patient's sample were found to be negative.

The donor was again recalled at the blood center and a repeat sample was taken. A saliva sample was taken for secretor status.

Repeat testing also confirms the presence of weak B on red cells and saliva testing for secretor status shows H secretor only.[5]

   Discussion Top

ABO subgroups are phenotypes that differ in the amount of A and B antigens carried on red cells and present in secretions. Subgroups of B are very rare and much less frequent than A subgroups. Subgroups of B are usually recognized by variations in the strength of the reaction using anti-B and anti-A, B. Inheritance of B subgroups, is considered to be a result of alternate alleles at the B locus.[6] Criteria used for differentiation of weak B phenotypes include the following serologic techniques: (1) strength and type of agglutination with anti-B, anti-A, B, and anti-H; (2) presence or absence of ABO isoagglutinins in the serum; (3) adsorption–elution studies with anti-B; (4) presence of B substance in saliva; and (5) molecular testing.

Here, in this case, blood group is confirmed as a weaker subtype of B. No reaction is seen at room temperature and 37°C with B cells, but at 4°C, weak-positive reaction is seen with B cells in reverse grouping. This positive reaction is probably due to anti-B present in the serum whose activity is enhanced at 4°C as it is immunoglobulin M in nature. This anti-B is only causing group discrepancy but is clinically insignificant.

The pattern shows probable blood group is Bx.[7] Since we could not perform molecular testing, the exact subtype of B could not be determined.

This study shows the importance of doing both cell grouping (forward) and serum grouping (reverse) for resolving group discrepancy problems. This study also illustrates the application of special serological tests such as adsorption–elution and saliva testing for secretor status to detect weak subgroups.

This subgroup, if transfused to group 'O' recipients, can result an adverse haemolytic transfusion reaction. On the contrary, when this individual present as transfusion recipients, he should be transfused with group 'O' red cell components and group matched/compatible plasma and platelet components.[8]

   Conclusion Top

Any discrepancy in blood grouping must be checked by tube method. This study shows the importance of both cell and serum grouping in detecting possible blood group discrepancies. Special serological tests such as cold adsorption and heat elution techniques are useful tools in detecting rare subtypes of B. Detection of weaker subgroups of ABO system will help blood centres to establish defined transfusion protocol and prepare an elaborate rare blood donor registry.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the donor has given his consent for images and other clinical information to be reported in the journal. The donor understands that name and initials will not be published and due efforts will be made to conceal patient identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

Marionneau S, Cailleau-Thomas A, Rocher J, Le Moullac-Vaidye B, Ruvoën N, Clément M, et al. ABH and Lewis histo-blood group antigens, a model for the meaning of oligosaccharide diversity in the face of a changing world. Biochimie 2001;83:565-73.  Back to cited text no. 1
Cai XH, Jin S, Liu X, Shen W, Lu Q, Wang JL, et al. Molecular genetic analysis for the B subgroup revealing two novel alleles in the ABO gene. Transfusion 2008;48:2442-7.  Back to cited text no. 2
Beattie KM. Identifying the cause of weak or “missing” antigens in ABO grouping tests. The Investigation of Typing and Compatibility Problems Caused by Red Blood Cells. Washington, DC: AABB; 1975. p. 15-37.  Back to cited text no. 3
Judd WJ, Johnson ST, Storry JR. Judd's Methods in Immunohematology. 3rd ed. Bethesda, MD: AABB Press; 2008.  Back to cited text no. 4
Claudia SC, Meghan D, Susan T, Johnson MK. Testing saliva for A, B, H, Lea, and Leb antigens. Methods 2-8. 20th ed. Bethesda, MD: AABB Technical Manua; 2020.  Back to cited text no. 5
Hosseini-Maaf B, Letts JA, Persson M, Smart E, LePennec PY, Hustinx H, et al. Structural basis for red cell phenotypic changes in newly identified, naturally occurring subgroup mutants of the human blood group B glycosyltransferase. Transfusion 2007;47:864-75.  Back to cited text no. 6
Watkins WM. The ABO blood group system: Historical background. Transfus Med 2001;11:243-65.  Back to cited text no. 7
Chaurasia R, Rout D, Dogra K, Coshic P, Chatterjee K. Discrepancy in blood grouping: subgroups of B-challenges and dilemma. Indian J Hematol Blood Transfus 2017;33:628-9.  Back to cited text no. 8

Correspondence Address:
Sourav Mukherjee,
Department of Transfusion Medicine and Blood Centre, Peerless Hospitex Hospital 360, Panchasayar, Kolkata 700094
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ajts.ajts_21_21


  [Figure 1]

  [Table 1], [Table 2]


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