SIGNIFICANCE OF DETECTION AND RESOLUTION OF BLOOD GROUP DISCREPANCIES Sazia Samir, Ashish Jain, Neelam Marwaha, R.R. Sharma Dept of Transfusion Medicine, PGIMER, Chandigarh

Introduction ABO discrepancy: The ABO system is the first recognized blood group system in humans. In 1901, Karl Landsteiner showed that an individual’s serum contained ABO- antibodies corresponding to the antigen(s) which are lacking on his red blood cells (RBCs). The Anti-A and anti-B antibodies are naturally occurring which usually appear from the age of approximately 6 months in immunocompetent individuals. These are predominantly IgM type, but IgG or IgA type are also commonly found. ABO discrepancy: ABO discrepancies occur when the reactions in forward grouping are not corroborative to those in the reverse grouping. Determination of correct ABO blood group of a donor in relation to reverse grouping is essential for preventing ABO incompatible transfusion reactions and preventing organ transplant rejections.

Introduction Rh blood group system: D antigen is the most immunogenic and clinically important because of the ability of anti-D to cause transfusion reactions and haemolytic disease of the foetus and newborn (HDFN). RhD typing discrepancies cause a significant problem during routine testing due to its weaker variants which include: Partial D variant, Weak D variant and Del phenotype. Resolution of D antigen status is necessary to assign the appropriate antigen status (D positive or D negative) to the donor and in administering appropriate product to the patient.

AIMS This was a retrospective study to determine the frequency and cause of ABO discrepancies in donor samples and to know the prevalence of weaker subgroups of A and B. We also determined the frequency of ‘weak D’ and frequency of alloantibodies (including their specificities and titer) in RhD negative donor samples which gave a positive result on an indirect antiglobulin test (IAT).

Methods This was a retrospective study on donor samples collected from 1stApril, 2013 to 30th September, 2015 (two and a half years). When a discrepancy was observed in ABO and RhD grouping using a fully automated immunohematology analyzer, the sample was handed over to special immunohematology lab for further resolution. The blood grouping was repeated using tube technique using commercial antisera. Adsorption-elution testing was done for detecting weak subgroups of A/B. Antibody screen (3-cell) and identification (11-cell) was done by gel technique (Bio-Rad, Switzerland). For RhD negative samples, a ‘Weak D’ testing, extended Rh typing (C, c, E, e), alloantibody specificity and typing for other RBC antigens (K, Jka, Jkb, Fya, Fyb, M, N, S, etc.) were also performed by gel technique. The donor details (name, age, registration/unit number) were checked to avoid repetition while data analysis.

Results In the study, 104 (0.072%) ABO discrepancies were observed, which were further distributed according to standard classification into Group I, II and IV discrepancies. Sr. No. ABO discrepancies Number (n=104) Frequency and rate as a fraction of total ABO discrepancies (n=104) Frequency and rate as a fraction of total donations (n=144279) 1 Group I discrepancy Frequency (%) Rate Frequency (%) 57 Weak anti-A antibody 24 23.07 1 In 4.33 0.016 1 in 6011 Weak anti-B antibody 33 31.73 1 in 3.15 0.022 1 in 4372 2 Group II discrepancy 29 Weak subgroups of A 1 in 4.33 Weak subgroups of B 5 4.8 1 in 20.8 0.0034 1 in 28855 3 Group IV discrepancy 18 17.3 1 in 5.77 0.012 1 in 8015 There was no discrepancy which could be classified as group III. Out of the total 144279 donor samples tested, 135043 (93.6%) were RhD positive and 9236(6.4%) were RhD negative.

Serological details of Weak Subgroups of A and B Weak Subgroups of A (n=24) Weak Subgroups of B (n=5)

Antibody Specificities and titer in group IV discrepancies (n=16) Alloantibody Specificity No. of samples (N=18) Percent (%) RhD typing Titer (number of samples) Anti-M 5 27.77 Positive (n=7) 1 (n=3); 2 (n=1); 16 (n=1) 1 (n=1) Anti-Lea 1 5.55 Anti-H 16 (n=1) Anti-D 7 38.88   Negative (n=11) 1 (n=2); 2 (n=1); 8 (n=2); 128 (n=2) Anti-D + anti-C 2 11.11 Anti-D: 2 and 8 (n=1) Anti-C: 1 and 2 (n=1) Anti-D + anti-E Anti-D: 8; anti-E: 2 (n=1) Anti-N One sample was found to be of Bombay’ (Oh) phenotype (frequency of 0.96%) giving a strong agglutination (4+) with O cells.

Working algorithm for detection and resolution of blood group discrepancies

Discussion This retrospective study of blood group discrepancies on 144279 donor samples is the largest one reported on the literature from our country. Weak anti-B antibodies was the most common cause of ABO discrepancy in our study (31.73%), as was in the study by Sharma et al (58.8%). This type of discrepancy falls under group I and is more common than the others. In all the studies, weak subgroup of A was more frequent than the weak subgroup of B. Author Year Sample size Frequency of ABO discrepancies Frequency of weak subgroups (A and B) Rate of weak subgroups of A B Thakral et al 2005 86687 Not determined 0.02% 1 in 43344 to 1 in 14448 1 in 86687 Sharma et al 2013 104010 0.04% 0.01% Kaur et al 44425 0.06% 1 in 11106 to 1 in 44425 1 in 22212 to 1 in 44425 Present study 2018 144279 0.072% 0.012% 1 in 6011 1 in 28855

Conclusion To the best of our knowledge, this was the first and largest study in donor population where the ABO blood group discrepancies were grouped according to a standard classification. Identification of weak subgroups of ABO system helps avoiding ‘mistyping' of blood components specially the donor red cell units which can potentially lead to haemolytic transfusion reaction in the recipient if not detected. The weak subgroups of A and B identified in our study require further confirmation by molecular studies, which may help in better understanding of alleles and the genetic mutations occurring in our population.

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