An Unusual Case of ABO Discrepancy: Lessons Learnt
Vandana Puri1, Shivali Sehgal2, Maria Khatoon3, Geetika Sharma4, Sarita Deorari5
1 Assistant Professor, Department of Blood Bank and Pathology, Lady Hardinge Medical College, New Delhi, Delhi, India.
2 Assistant Professor, Department of Blood Bank and Pathology, Lady Hardinge Medical College, New Delhi, Delhi, India.
3 Senior Resident, Department of Blood Bank and Pathology, Lady Hardinge Medical College, New Delhi, Delhi, India.
4 Assistant Professor, Department of Blood Bank and Pathology, Lady Hardinge Medical College, New Delhi, Delhi, India.
5 Blood Bank Officer, Department of Blood Bank, Northern Railway Central Hospital, New Delhi, Delhi, India.
NAME, ADDRESS, E-MAIL ID OF THE CORRESPONDING AUTHOR: Dr. Shivali Sehgal, Assistant Professor, Department of Pathology, Lady Hardinge Medical College, New Delhi-110029, Delhi, India.
E-mail: shivalisehgal@gmail.com
Dear Editor,
During the pre-transfusion testing, ABO blood group typing is mainly done by agglutination. Sometimes, weak agglutination reactions may be seen with the reagent antibodies, as a result of weak expression of A and B antigens on red cell surface. These antigens may lead to significant discrepancies in ABO typing during reverse and forward grouping.
A young male came for a regular voluntary blood donation to Blood Bank, Northern Railway Hospital, New Delhi, India. The blood group known to the donor was O+. The blood group was re-performed and on forward grouping, it was O+ while on reverse grouping, reaction with only B cells noted. This suggested presence of a weaker subgroup of “A”. He was referred to Blood Bank, Lady Harding Medical College for further work up. Similar results were obtained at three temperatures (4°C, 25°C and 37°C). His Direct Coombs Test (DCT) and Indirect Coombs Test (ICT) profile were negative. Anti H was strongly positive while that with anti A1 serum was negative [Table/Fig-1].
| Incubation time and temperature | Reactions of donor red cells with known antisera | Reactions of donor serum against reagent red blood cells |
|---|
| A | B | AB | H | A1 cells | B cells | O cells |
|---|
| At 22°C | 0 | 0 | 0 | 4+ | 0 | 3+ | 0 |
| At 37°C | 0 | 0 | 0 | 4+ | 0 | 3+ | 0 |
| 4°C (15 minutes) | 0 | 0 | 0 | 4+ | 0 | 3+ | 0 |
| 4°C (30 minutes) | 0 | 0 | 0 | 4+ | 0 | 3+ | 0 |
Key:0 = No red blood cell agglutination; 1+ to 4+ = Grades of red blood cell agglutination.
Red cells were subjected to adsorption-elution studies [1]. Polyclonal O and B group antisera were adsorbed to washed test red cells. Centrifugation at 3000 g for 5 minutes was done, supernatant was discarded. Adsorbed cells were washed six times with normal saline. The last supernatant was retained separately. Elution was done. This eluate and the last supernantant were kept in parallel and the reaction was seen with A, B, O cells separately. Agglutination with A cells and no reaction with B cells suggested presence of A subgroup. Final wash solution did not show agglutination with A, B and O cells thereby validating the test.
Weaker subgroups of A include A3, Ax, Ay, Aend, Am and Ael [2]. These are weaker than A2 and occur very infrequently (<1%) but they can be the cause of ABO discrepancy [3]. This patient showed no reaction with Anti A, B and AB; strong positivity with Anti H and no reaction with Anti A1. This suggested the possibilities of subgroups Ay, Am and Ael [Table/Fig-2].
Serological reactions observed in subgroups Ay, Am and Ael.
| Phenotypes | Testing of red cells | Naturally occurring antibodies in serum |
|---|
| Anti A | Anti B | Anti AB | Anti H | Anti A | Anti-B | Anti-A1 |
|---|
| A3 | mf 2+ | 0 | mf 2+ | 3+ | No | Common | Sometimes |
| Ax | Wk/0 | 0 | 2+ | 4+ | No | Common | Always |
| Aend | Wk mf | 0 | wk mf | 4+ | No | Common | Sometimes |
| Am | 0/wk | 0 | 0/+ | 4+ | No | Common | No |
| Ay | 0 | 0 | 0 | 4+ | No | Common | No |
| Ael | 0 | 0 | 0 | 4+ | Sometimes | Common | Yes |
Key: 0 = No red blood cell agglutination; wk= Weak red blood cell agglutination; 1+ to 4+ = Red blood cell agglutination of increasing strength; mf = mixed field pattern of agglutination
Identification of such weaker subgroups is necessary to avoid haemolytic transfusion reactions. The subgroup typing should include a series of tests as done in the present case. Identification of a weak reaction can be further facilitated by increasing the incubation time, lowering the reaction temperature and by treatment of red cells with enzymes. Confirmatory tests for diagnosing these weak subgroups are still beyond the scope of most of the Blood banks as the antisera for these are not routinely available. However, family studies, molecular studies and in certain cases, special tests like serum glycosyl transferase estimation can be helpful tools for confirmation of these subtypes [4].
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