Prevalence and Serological Characterisation of Weakly or Variably Expressed B Antigen (Weak B Subgroups) Among Blood Donors and Patients: A Systematic Review and Meta-Analysis

Background: The weak B subgroups — B3, Bx, Bm and Bel — carry reduced or atypical B antigen and react only weakly, or not at all, with anti-B, making them a recognised cause of ABO grouping discrepancy and of potential mistyping with transfusion-safety implications. Their reported frequency is inconsistent and has never been systematically synthesised. Methods: Following PRISMA 2020, PubMed, Embase, Scopus, Web of Science and Google Scholar were searched for studies reporting the frequency or serological characterisation of weak/variant B. Two reviewers independently screened and extracted data and appraised quality using the Joanna Briggs Institute checklist for prevalence studies. Study-level prevalence was expressed per 100,000 with exact (Clopper–Pearson) 95% confidence intervals (CIs); a random-effects (Freeman–Tukey) proportion meta-analysis was planned where three or more comparable cohorts were available. Results: In an Eastern Indian cohort of 84,534 donors, weak B occurred in 9 — 10.65 per 100,000 (95% CI 4.87–20.21), about 1 in 9,400 — ordered B3 > Bm > Bx = Bel; older Indian data report rarer figures (~1 in 24,000). A Chinese cohort of 2,945,643 samples reported all ABO subgroups at 31.47 per 100,000 (95% CI 29.48–33.56) and estimated that 27.81% were missed by routine testing. With only one comparable weak-B denominator, pooling criteria were not met; per-study estimates and a structured narrative synthesis are presented, and across the literature weak B characteristically presents as a forward/reverse discordance resolved by adsorption–elution, saliva testing and molecular analysis. Conclusion: Weakly expressed B antigen is rare (~1 in 9,000–24,000 donors) but routinely under-detected by low-sensitivity forward grouping. A definitive pooled prevalence awaits the full search; meanwhile, forward and reverse grouping should agree, confirmed by sensitive and molecular methods, before any B-containing group is reported. A practical resolution algorithm is provided to support transfusion services.

weak B subgroup; ABO discrepancy; reverse grouping; prevalence; transfusion safety

1. Storry, J. R., & Olsson, M. L. (2009). The ABO blood group system revisited: A review and update. Immunohematology, 25(2), 48–59. https://doi.org/10.21307/immunohematology-2019-231 [Google Scholar] [Crossref]

2. Seltsam, A., & Blasczyk, R. (2005). Missense mutations outside the catalytic domain of the ABO glycosyltransferase can cause weak blood group A and B phenotypes. Transfusion, 45(10), 1663–1669. https://doi.org/10.1111/j.1537-2995.2005.00558.x [Google Scholar] [Crossref]

3. Li, H.-Y., & Guo, K. (2022). Blood group testing. Frontiers in Medicine, 9, 827619. https://doi.org/10.3389/fmed.2022.827619 [Google Scholar] [Crossref]

4. Desai, P., Navkudkar, A., & Rajadhyaksha, S. (2024). ABO blood group discrepancies in blood donor and patient samples at a tertiary care oncology centre: Analysis and serological resolution. Hematology, Transfusion and Cell Therapy, 46(4), 402–407. https://doi.org/10.1016/j.htct.2023.07.011 [Google Scholar] [Crossref]

5. Thakral, B., Saluja, K., Bajpai, M., Sharma, R. R., & Marwaha, N. (2005). Importance of weak ABO subgroups. Laboratory Medicine, 36(1), 32–34. [Google Scholar] [Crossref]

6. Page, M. J., McKenzie, J. E., Bossuyt, P. M., Boutron, I., Hoffmann, T. C., Mulrow, C. D., et al. (2021). The PRISMA 2020 statement: An updated guideline for reporting systematic reviews. BMJ, 372, n71. https://doi.org/10.1136/bmj.n71 [Google Scholar] [Crossref]

7. Prevalence of “weak B” phenotypes and their evaluation and differentiation in healthy blood donor population in Eastern India. (2024). Asian Journal of Transfusion Science, 18(2), 225–229. https://doi.org/10.4103/ajts.ajts_36_23 [Google Scholar] [Crossref]

8. Wang, Z., Jin, S., Zheng, J., Qian, C., Cai, X., & Xiang, D. (2024). Prevalence and distribution of serological characteristics of weak ABO subgroups in the Chinese population. Hematology, Transfusion and Cell Therapy, 46, S115–S121. https://doi.org/10.1016/j.htct.2024.04.127 [Google Scholar] [Crossref]

9. Bhatia, H. M., & Sathe, M. S. (1974). Incidence of “Bombay” (Oh) phenotype and weaker variants of A and B antigen in Bombay (India). Vox Sanguinis, 27, 524–532. [Google Scholar] [Crossref]

10. Banerjee, S., Alwar, V. A., & Subramanian, S. (2021). The importance of testing for secretor status of ABH antigens: A case series. Iraqi Journal of Hematology, 10(2), 176–179. https://doi.org/10.4103/ijh.ijh_25_21 [Google Scholar] [Crossref]

11. Prasanth, V., Banerjee, P., Kaur, D., Kumari, D., Khiamniungan, C. B., Bhatia, J., Jain, A., & Negi, G. (2025). A or AB? Resolving the dilemma of weaker subgroup through serological evaluation: Reporting two cases from Uttarakhand. Asian Journal of Transfusion Science, 19(1), 154–157. https://doi.org/10.4103/ajts.ajts_154_23 [Google Scholar] [Crossref]

12. Meny, G. M. (2017). Recognizing and resolving ABO discrepancies. Immunohematology, 33(2), 76–81. [Google Scholar] [Crossref]

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