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Para-bombay blood group: Report of a rare blood group

1 Department of Haematology, School of Medical Sciences, Universiti Sains Malaysia, 16150 Kubang Kerian, Kelantan, Malaysia
2 Department of Haematology, School of Medical Sciences, Universiti Sains Malaysia; Transfusion Medicine Unit, Hospital Universiti Sains Malaysia, 16150 Kubang Kerian, Kelantan, Malaysia

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Date of Submission10-Jan-2021
Date of Decision29-Jun-2021
Date of Acceptance29-Aug-2021
Date of Web Publication04-Jun-2022


Para-Bombay blood group is a rare blood group typically characterized by the absence of H antigens on red blood cell and the presence of ABH substances on secretion. It can be easily missed and often mistaken as blood group O without extended testing. Detection is important as it significantly affect transfusion management. We report two cases of Para-Bombay A blood group in a teaching hospital in a North-Eastern state of Malaysia.

Keywords: Para Bombay, rare blood group, transfusion

How to cite this URL:
Joibi KF, Noor NH, Hassan MN, Iberahim S, Rahman WW, Yusoff SM, Ramli M, Bahar R, Nizam Akbar NA, Zulkafli Z. Para-bombay blood group: Report of a rare blood group. Asian J Transfus Sci [Epub ahead of print] [cited 2022 Dec 4]. Available from:

   Introduction Top

Bombay and Para-Bombay blood group are rare blood phenotypes which are seen more in Asia particularly India where Bombay phenotype are more common and in East Asian countries where Para-Bombay phenotype are more than in other regions.[1] Classical Bombay phenotype is defined by the complete absence of H antigens in both red blood cells (RBCs) and body secretions resulted from silenced FUT1 (H gene) and FUT2 (Se gene). A closely linked phenotype, the Para-Bombay, is characterized genetically by mutated FUT1 with or without a functioning FUT2, or a silenced FUT1 gene with a functioning FUT2 gene. Phenotypically, they either have a complete lack of ABH antigens on RBCs with the presence of ABH substances in body fluids or by having small amount of ABH antigens on RBCs with or without the presence of ABH substances in secretions.[1],[2] The concurrent inheritance of A or B genes gives rise to either Para-Bombay A or B.[2] Para- Bombay phenotype was often suspected when there is discordant finding between the forward and reverse grouping.[1],[3],[4] We reported two cases of Para-Bombay phenotype in our center that was detected because of discrepant forward and reverse typing.

   Case Report Top

The first patient is a 79-years-old female of Malay ethnicity with no known previous medical illness. She is para seven with her last childbirth was 30 years ago. She has no history of blood transfusion and no history of rare blood group in the family. She initially presented with anemic symptoms (lethargy, dyspnea, and angina pain). She was treated for anemic-induced angina complicated with findings of renal failure with metabolic acidosis and hyperkalemia. Hb level on admission was 4.6 g/dL. Hemodialysis was planned for her with transfusion of 2-pint packed cells during hemodialysis. However, the sample sent for blood grouping revealed ABO discrepancy between the forward and reverse grouping. Forward grouping at room temperature done using column agglutination method showed forward grouping of O Rh D positive and reverse grouping of blood group A. Results of her extended immunohematology work up as shown in [Table 1].
Table 1: Results of extended blood grouping for first patient

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Collectively, results were concluded as Para-Bombay A with no anti-H detected. Before transfusion, anti-H reactivity was tested at different temperatures (4°C, room temperature, and 37°C) with O RBC and showing no reactions in all three temperatures. She was transfused with two pints of AHG compatible group O RhD positive due to urgency and lack of the availability of Bombay blood units with no transfusion reaction.

The second patient is a 31-year-old female, primigravida, of Malay ethnicity with a background history of endometriosis and adenomyosis at 25 weeks of gestation. There was no previous history of transfusion or rare blood group in the family. She presented with premature prelabor rupture of the membrane. She delivered through spontaneous vaginal delivery; however, it was complicated with retained placenta. Manual removal of retained placenta was done under general anesthesia with estimated blood loss of 400 ml. In view of low preoperative hemoglobin level of 10.0 g/dL, she was planned for blood transfusion.

Initial blood grouping done at room temperature showed discrepancy in forward and reverse grouping. Forward showed blood group O RhD positive presence of extra antibodies in the reverse grouping. Results of her extended immunohematology work up shown in [Table 2]. Collectively the results were concluded as Para-Bombay A with anti-IH.
Table 2: Results of extended blood grouping for second patient

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   Discussion Top

Para-Bombay is a rare phenotype often discovered when there is ABO discrepancy between forward and reverse grouping. The first case remained undetected most throughout her adult life as she has no known medical illness and no prior history of requiring transfusion before the current presentation. We were unable to obtain records of blood grouping done from her previous hospital admission for delivery. Further extended blood grouping using anti-H in which there was no reaction raised the suspicion of a Bombay/Para-Bombay phenotype as opposed to subgroup as subgroup would have a stronger reaction with anti-H lectin.[2]

Para-Bombay persons would occasionally have weak ABH substances detected on RBCs resulting from passive adsorption from secretion, often discernible using adsorption-elution methods.[4],[5] Saliva secretor testing can demonstrate the secretor status of the suspected patient and plays some role in differentiating whether the patient is of Bombay or Para-Bombay phenotype. Bombay phenotype has a silenced FUT2/Se gene hence the detection of ABH substances is more suggestive of a Para-Bombay phenotype.[1],[6] Both our patients demonstrated ABH substances in their saliva. Secretor status can also be determined by typing for Lewis antigen as nonsecretors will type as Le (b-). However, Lewis phenotyping was not done for both patients. A caveat for distinguishing Para-Bombay from Bombay phenotypes using secretor status is that there are cases of Para-Bombay characterized from an H-weak nonsecretor (Hw/h, se/se) and H-deficient, weak secretor (hh, Sew/se).[6]

Often, there are also reported cases of it being missed due to the patient being mistakenly grouped as blood group O resulted from the failure of detection of weak ABH antigens on the RBCs.[5] In the second case, Para-Bombay phenotype was missed, and the patient was typed as blood group O RhD positive during her earlier antenatal visits. However, her antibody screening showed panagglutination which lead to further immunohematological investigation. This patient would have been regarded as group O RhD positive rather than Para-Bombay A without the use of anti-H lectin. Therefore, this case provided an example on why anti-H lectin should be wisely utilized in blood grouping, especially when there is ABO discrepancy.[7],[8]

A distinguishing feature between both cases is the absence of anti-H in the first case while in the second case, an anti-IH was detected. Para-Bombay persons may develop anti-H, anti-IH, or the combination of both on top of having naturally occurring anti-A/anti-B.[4] The anti-H usually has weaker reactivity when compared to the anti-H in Bombay phenotype, although it may be reactive at 37°C (2). Generally, anti-H or anti-IH may have wide thermal amplitude with reactivity at 4°C, 22°C, and 37°C but predominantly are reactive at the colder temperature. Detecting these antibodies have significant implications in the transfusion therapy of the patients. In an urgent situation, in which a patient with an anti-H/anti-IH which predominantly reacts at colder temperature and not at body temperature (37°C), ABO blood groups which are AHG compatible can be given.[4],[7] Our first patient was urgently transfused with AHG compatible blood group O RhD positive blood without any transfusion reactions. Before transfusion, anti-H reactivity was tested at different temperatures (4°C, room temperature, and 37°C) with O red cells showing no reactions in all three temperatures. Unfortunately, due to unavailability, we did not test patient's red cells with the serum of a Bombay phenotype. Nevertheless, Para-Bombay blood group should be transfused with Bombay/Para-Bombay units if alloantibody anti-H and anti-IH present are clinically significant (reacting at 37oC).[4]

Fortunately, the second patient did not require any transfusion during this admission. Anti-IH was detected because of the reactivity of her serum toward adult O cells and nonreactivity toward cord O cells which do not possess the I antigen.[2],[4]

Therefore, in areas where rare blood is not easily obtainable for example being in a location far from a referral center where there is access to rare blood units, other alternatives should be considered if any urgent need arises. Measures include testing family members for eligible donors, keeping as frozen storage if facilities are available or considering autologous transfusion.[9]

   Conclusion Top

In blood bank, ABO grouping is among the most important test. Therefore, any ABO discrepancies should be regarded as a highly important issue to be resolved. The availability of reagents, for example, anti-H Lectin and O cells supplemented by tests such as saliva secretory tests and adsorption-elution tests should be available in most blood transfusion services in further investigating a suspected Bombay/Para-Bombay phenotype as it has significant transfusion implications. In cases where there is difficulty in confirming a Bombay/Para-Bombay phenotype, there is a role for molecular testing.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

Patel JN, Donta AB, Patel AC, Pandya AN, Kulkarni SS. Para-Bombay phenotype: A case report from a tertiary care hospital from South Gujarat. Asian J Transfus Sci 2018;12:180-2.  Back to cited text no. 1
[PUBMED]  [Full text]  
Harmening DM. Modern Blood Banking and Transfusion Practices. FA Davis; 2018.  Back to cited text no. 2
Arumugam P, Hamsavardhini S, Ravishankar J, Bharath R. Resolving ABO discrepancies by serological workup-an analysis of few cases. Int J Res Med Sci 2017;5:893-900.  Back to cited text no. 3
Subramaniyan R. AB Para-Bombay phenotype: A rare blood group variant and its clinical significance. Hematol Transfus Cell Ther 2018;40:96-7.  Back to cited text no. 4
Chacko MP, Mathan A, Daniel D. Para-Bombay: A blind spot in blood grouping? Asian J Transfus Sci 2011;5:182-3.  Back to cited text no. 5
[PUBMED]  [Full text]  
Simon TL, McCullough J, Snyder EL, Solheim BG, Strauss RG. Rossi's Principles of Transfusion Medicine. Wiley-Blackwell: John Wiley and Sons; 2016.  Back to cited text no. 6
Yashovardhan A, Kumar IC, Babu KS, Babu BS, Verma A, Kumar BS, et al. Para-Bombay phenotype: Report of a rare blood group. J Clin Sci Res 2012;1:141.  Back to cited text no. 7
Kim MS, Kim JS, Park H, Chung Y, Kim H, Ko DH, et al. The first case of Para-Bombay blood type encountered in a Korean tertiary hospital. J Korean Med Sci 2019;34:e258.  Back to cited text no. 8
Paccapelo C. Managing a rare donor programme: The immunohaematology laboratory perspective. ISBT Sci Ser 2018;13:11-5.  Back to cited text no. 9

Correspondence Address:
Noor Haslina Mohd Noor,
Transfusion Medicine Unit, Hospital Universiti Sains Malaysia, 16150 Kubang Kerian, Kelantan
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ajts.ajts_3_21


  [Table 1], [Table 2]


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