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 Table of Contents  
Year : 2020  |  Volume : 11  |  Issue : 3  |  Page : 112-115

Prevalence of A2and A2B subgroups along with anti-A1antibody in patients and donor population and its clinical significance

Department of Transfusion Medicine, All India Institute of Medical Sciences, Bhubaneswar, Odisha, India

Date of Submission14-Feb-2020
Date of Decision25-Mar-2020
Date of Acceptance13-Apr-2020
Date of Web Publication16-Sep-2020

Correspondence Address:
Dr. Somnath Mukherjee
Department of Transfusion Medicine, All India Institute of Medical Sciences, Bhubaneswar, Odisha
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/joah.joah_15_20

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BACKGROUND: The clinical significance of anti-A1antibody among A2and A2B subgroups is controversial. Few case reports have shown clinically significant anti-A1antibody at 37°C, causing hemolysis of donor red cells. The present study aims to find the prevalence of A2and A2B and the clinical significance of anti-A1antibody in these subgroups of A.
MATERIALS AND METHODS: This prospective observational study was done in a tertiary care center in the eastern part of India. Gold standard test tube technique was used to determine blood group and distinguish A1from A2based on agglutination reaction with anti-A1lectin. Serum of A2and A2B subgroups was tested with A1red cells to confirm the presence of anti-A1antibodies. Further testing of anti-A1antibody was also performed to determine whether the antibody is IgM or IgG and of any clinical significance.
RESULTS: A total of 2874 blood samples of both patients and donors were analyzed. Among A blood group, 98.4% were A1 and, whereas 1.6% were A2, whereas among AB blood group, A1B and A2B were 93.9% and 6.1%, respectively. Only 3 out of 13, A2B patients (23.07%) showed the presence of anti-A1antibody but without any clinical significance.
CONCLUSIONS: Our study could not find any clinically significant anti-A1antibodies. Thus, we insinuate any requirement of mandatory testing for the determination of A1, A2,and anti-A1antibodies. Subtyping will help in the use of A2donor for renal transplant in O and B group patients and the use of A2platelets also in O and B group patients.

Keywords: ABH blood group, blood group A enzyme, isoantibodies, lectins

How to cite this article:
Mishra D, Prakash S, Sahoo D, Ray GK, Routray SS, Das PK, Mukherjee S. Prevalence of A2and A2B subgroups along with anti-A1antibody in patients and donor population and its clinical significance. J Appl Hematol 2020;11:112-5

How to cite this URL:
Mishra D, Prakash S, Sahoo D, Ray GK, Routray SS, Das PK, Mukherjee S. Prevalence of A2and A2B subgroups along with anti-A1antibody in patients and donor population and its clinical significance. J Appl Hematol [serial online] 2020 [cited 2020 Dec 3];11:112-5. Available from: https://www.jahjournal.org/text.asp?2020/11/3/112/295116

  Introduction Top

It has been more than a century ago, ABO blood group system was discovered, but still, ambiguity remains in immunohematology while detection of ABO subtypes or weaker variants. The expression of ABO blood group antigens is due to carbohydrate moieties present on red blood cell surfaces, and these antigens are also found in various tissues or cells such as epithelium, vascular endothelium, and platelets.[1] The subgroup of A and AB blood groups arises due to polymorphism in the genes encoding for the ABO blood group system (A and B genes), which leads to the diminished amount of A or B antigens on red blood cells. A1 and A2 are the major subgroups of A and AB blood groups, which differ both qualitatively and quantitatively.[2] Red cells of both A1 and A2 subgroups react strongly with the monoclonal anti-A reagent. Based on reactivity with lectin from Dolichos biflorus seeds, A and AB blood groups are divided into A1 and A2 major subgroups. The D. biflorus lectin specifically agglutinates A1 red cells but will not agglutinate A2 red cells. Different studies from India show that the frequency of A1 and A2 subgroups among A blood group was 98.14% and 1.07%, respectively, whereas among AB group, the frequency of A1B was 89.28% and that of A2B was 8.99%.[3]

Anti-A1 antibodies appear as atypical cold agglutinins (react at room temperature), sometimes present in the sera of A2 or A2B individuals who lack the corresponding antigen.[4] Approximately, 0.4% of A2 and 25% of A2B individuals have anti-A1 in their serum, and these antibodies become clinically significant when they react at 37°C, leading to hemolysis of A1 red cells.[4],[5],[6] A1 adults have approximately 0.8 × 106 antigen sites per red cell, whereas A2 adults have 0.24 × 106 antigen sites per red cell, which is comparable to the number of antigen sites per red cell seen in A1 neonates, i.e., 0.25–0.37 × 106. Hence, newborn red cells may not or weakly react with anti-A1 reagents.[7] In the eastern part of India, there are few studies conducted only on blood donors for the prevalence of A1 and A2 subgroups. Therefore, this study was conducted with the objectives of the estimation of the prevalence of A1 and A2 subgroups along with anti-A1 antibody among both A and AB blood groups in donor and patient population and to find the presence of any clinically significant anti-A1 antibody in same blood group donor and patient population.

  Materials and Methods Top

Study design and study setting

This prospective observational study was conducted in the department of transfusion medicine from June 2017 to January 2019 in a tertiary care hospital, Odisha, one of the states in the eastern part of India. A total of 2874 blood samples of both donors and patients of A and AB blood groups were included in our study. Thirty-two blood samples of the neonate with four A2 and three A2B were excluded from the study. This is because ABO antigens are not fully developed at birth, and red cells of neonates of the A1 blood group may not react or react weakly with anti-A1.

Ethical permission and further testing procedures

Ethical permission was obtained from the institute's ethical committee before the initiation of the study. Informed consent was obtained from all the donors and patients. Blood grouping was done using the test tube technique as it is still considered as the gold standard. The forward grouping was done using monoclonal antisera anti-A, anti-B, anti-AB, and anti-D (Tulip Diagnostics, Goa, India), and reverse grouping was done using in-house prepared pooled A cells, B cells, and O cells. Blood samples of groups A and AB were further tested with anti-A1 lectin (Tulip Diagnostics, Goa, India) to classify them into A1 and A2 subgroups, considering the fact that after A1, A2 is most common.[8] Visible agglutinations with monoclonal anti-A reagents and no agglutination with anti-A1 were considered as A2 subgroups. Further, the plasma of A2 and A2B subgroups was tested with A1 red cells to confirm the presence of anti-A1 antibodies. The thermal amplitude of anti-A1 antibodies was determined by keeping the test tubes at 4°C, 22°C, and 37°C. The methodology of sample testing is shown in [Flowchart 1].

  Results Top

A total of 2874 blood samples from A and AB blood groups of both patients and donors were analyzed with 2321 of A blood group and 553 of AB blood group, respectively. Among A blood group, 2284 were A1, whereas rest 37 were A2. A1B and A2B were 519 and 34, respectively [Table 1]. Out of 2028 donors, the prevalence of A1, A2,A1B, and A2B was 98.9%, 1.1%, 94.7%, and 5.3%, respectively. Among 846 patients, A1 and A2 were 97.2% and 2.8%, whereas A1B and A2B subtypes were 91.6% and 8.4%, respectively. None of the A2 blood group donors or patients had anti-A1 antibody in their serum, whereas 3 out of 13 (23.07%) A2B patients had anti-A1 antibody. These anti-A1 antibodies were not clinically significant as they were not showing agglutination at 37°C [Table 2].
Table 1: Prevalence of A2 and A2B subgroups among A and AB blood groups (n=2874, A=2321, AB=553)

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Table 2: Prevalence of anti-A1 antibody in A2 and A2B subgroups

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  Discussion Top

A and AB blood groups were subdivided into major subgroups such as A1 and A2. These subgroups are equally reactive with monoclonal anti-A reagents. Anti-A1 lectin reagent obtained from D. biflorus seeds is required to identify the subgroups of A and AB. The prevalence of A2 was found to be 1.6% and 6.1%, respectively, among A and AB blood groups, which is similar to another study conducted in South India by Shamee S et al.[4] In other studies, the prevalence of A2 and A2B among blood donors was depicted as 4.1%–5.8% and 19.2%–31.5%, respectively.[8],[9] In this study, the prevalence of A1 and A2 among A blood group was comparable with a study from Giriyan et al., whereas the prevalence of A1B and A2B among AB blood group was slightly higher.[10] The higher prevalence of the A2B subgroup than A2 could be explained by the suppression of A1 activity by the presence of a strong B gene.[11]

The prevalence of A1 and A2 between donors and patients was almost similar in our study population. Individuals with an A2B phenotype are more likely to produce anti-A1 than A2 phenotype because of the relative reduction of A antigens on A2B cells.[12] In this study, anti-A1 antibodies were detected in 3 out of 13 A2B patients only, and none of them showed reactivity at 37°C. Shastry and Bhat also found anti-A1 in 1.8% of A2 and 3.75% of A2B individuals, but none of them were clinically significant.[4] The genetic basis of high prevalence of anti-A1 antibodies in A2B is due to the *R101 allele. This allele is present in 41% of A2B individuals as compared to A2 (1%).[13] Furthermore, the *R101 allele is expressed in A1(*R101/*O) and A2(*R101/*B) individuals as heterozygote with O allele and B allele, respectively. A2 and A2B individuals sometimes produce blood group discrepancies due to the presence of Anti-A1 antibodies.[14] This type of blood group discrepancy was detected in three A2B patients, and none of our A2 study individuals have an anti-A1 antibody in their serum. These discrepancies are mainly seen in reverse typing and resolved by using A2 pooled cells instead of A1. Anti-A1 antibodies are generally cold agglutinins and react at room temperature. However, they rarely become clinically significant when they react at 37°C, and the extensive destruction of A1 cells has also been reported.[15],[16] Hence, typing with anti-A1 lectin will be required only in patients showing incompatible crossmatch in the anti-human globulin (AHG) phase. The patients with clinically significant anti-A1 antibodies should be transfused with either A2 or O blood group in case of A2 recipients, and A2B recipients should receive AHG crossmatch-compatible red cells of group A2B, B, A2, or O.[6],[14],[17] As we did not find any clinically significant anti-A1 antibody in either A2 or A2B subgroups, the effort toward distinguishing between A1 and A2 and testing for the presence of anti-A1 is not that much relevant in this population. A similar conclusion has also been envisaged that in a resource-poor country like India, routine subgrouping of A and AB is not advisable.[18] After A1, A2 is the most common subgroup of A with prevalence of 80% and 20%, respectively. Other subgroups such as A3 and Aend are very rare with a prevalence of 1:14,448 and 1:43,344, respectively. A3 subgroups are identified serologically as large agglutinates like a bunch of grapes in the background of a large number of free cells known as mixed field appearance.[2] In our study, we could not find any subgroups of A with mixed field appearance, suggesting the rarity of this subgroup. Various literatures have described that even A2 blood donors have donated kidney successfully to O and B patients.[19] Therefore, subtyping will help in the optimum use of A2 donor as a prospective donor for renal transplants in O and B group patients.[20] Moreover, subtyping will also help in managing platelet inventory as A2, and A2B platelets can be safely transfused with good recovery and corrected count increment in O and B group patients, respectively.[21] However, it is recommended to further perform subtyping of group A in some critical situations such as anti-A1 lectin negative weaker subgroups of A, i.e. (Aint-O) incompatible solid organ transplantation, where reports of hyperacute rejection of A subgroup renal allografts in O recipients were acknowledged.[22]

  Conclusions Top

To the best of our knowledge, the importance of identification of A2 and A2B subgroups along with anti-A1 antibody among blood donors as well as patient populations has never been explored from the eastern part of India. The findings from our study suggest that routine identification of anti-A1 antibody in A2 and A2B subgroups is not necessary. However, it is judicious to perform subtyping of A and AB along with the identification of anti-A1 antibody in organ transplant settings.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Storry JR, Olsson ML. The ABO blood group system revisited: A review and update. Immunohematology 2009;25:48-59.  Back to cited text no. 1
Thakral B, Saluja K, Bajpai M, Sharma RR, Marwaha N. Importance of weak ABO subgroups. Lab Med 2005;36:32-4.  Back to cited text no. 2
Elnour MA, Ali NY, Mohammed HA, Hummeda SA, Alshazally WY, Elderdery AY. Frequency of the A2-subgroup among blood group a and blood group AB among students of faculty of medicine and health sciences at Alimam Almahadi university, White Nile, Sudan. Hematol Transfus Int J 2016;1:104-6. DOI: 10.15406/htij.2016.01.00022.  Back to cited text no. 3
Shastry S, Bhat S. Imbalance in A2 and A2B phenotype frequency of ABO group in South India. Blood Transfus 2010;8:267-70.  Back to cited text no. 4
Rudmann SV. Textbook of Blood Banking and Transfusion Medicine. 1st ed. USA: WB Saunders; 1995. p. 73-5.  Back to cited text no. 5
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Mahapatra S, Mishra D, Sahoo D, Sahoo BB. Study of prevalence of A2, A2B along with major ABO blood groups to minimize the transfusion reactions. Int J Sci Res 2016;5:189-90.  Back to cited text no. 8
Chaitanya Kumar IS, Yashovardhan A, Suresh Babu B, Verma A, SreedharBabu KV, JothiBai DS. The prevalence of A2 and A2B subgroups in blood donors at a tertiary care teaching hospital blood bank of Rayalasemma region: A pilot study. J Clin Sci Res 2012;1:50.  Back to cited text no. 9
Giriyan SS, Agrawal A, Bajpai R, Nirala NK. A1 and A2 Sub-types of blood group 'A': A reflection of their prevalence in North Karnataka Region. J Clin Diagn Res 2017;11:40-2.  Back to cited text no. 10
Voak D, Lodge TW, Reed JV. A possible explanation for the expression of A2B phenotypes observed in some populations. Vox Sang 1970;18:471-4.  Back to cited text no. 11
Hosseini-Maaf B, Hellberg A, Rodrigues MJ, Chester MA, Olsson ML. ABO exon and intron analysis in individuals with the AweakB phenotype reveals a novel O1v-A2 hybrid allele that causes four missense mutations in the A transferase. BMC Genet 2003;4:17.  Back to cited text no. 12
Ogasawara K, Yabe R, Uchikawa M, Bannai M, Nakata K, Takenaka M, et al. Different alleles cause an imbalance in A2 and A2B phenotypes of the ABO blood group. Vox Sang 1998;74:242-7.  Back to cited text no. 13
Cooling L. ABO, H and Lewis structurally related antigens. In: Fung M, Grossman B, Hillyer C, Westhoff C, editors. Technical Manual. 18th ed. Bethesda: AABB; 2018. p. 295-7.  Back to cited text no. 14
Helmich F, Baas I, Ligthart P, Bosch M, Jonkers F, de Haas M, et al. Acute hemolytic transfusion reaction due to a warm reactive anti-A (1). Transfusion 2018;58:1163-70.  Back to cited text no. 15
Preece J, Magrin G, Webb A, Akers C, Davis A. Transfusion medicine illustrated. A bloody mistake: Unrecognized warm reactive anti-A1 resulting in acute hemolytic transfusion reaction. Transfusion 2011;51:914-5.  Back to cited text no. 16
Guidelines for Pretransfusion Laboratory Practice. Version: 5th ed. Australian and New Zealand Society of Blood Transfusion. Available from: https://www.anzsbt.org.au/data/documents/guidlines/PLP_Guidelines_Mar07.pdf. [Last accessed on 2019 Jul 16].  Back to cited text no. 17
Hazarika R, Basu S, Kaur P. Subgrouping of A and AB blood groups in Indian blood centres: Is it required? J Indian Med Assoc 2011;109:561-2.  Back to cited text no. 18
Sorensen JB, Grant WJ, Belnap LP, Stinson J, Fuller TC. Transplantation of ABO group A2 kidneys from living donors into group O and B recipients. Am J Transplant 2001;1:296-9.  Back to cited text no. 19
Redfield RR, Parsons RF, Rodriguez E, Mustafa M, Cassuto J, Vivek K, et al. Underutilization of A2 ABO incompatible kidney transplantation. Clin Transplant 2012;26:489-94.  Back to cited text no. 20
O'Donghaile D, Kelley W, Klein HG, Flegel WA. Recommendations for transfusion in ABO-incompatible hematopoietic stem cell transplantation. Transfusion 2012;52:456-8.  Back to cited text no. 21
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  [Table 1], [Table 2]


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