ABO blood group discrepancies: Study of prevalence and related factors

Background: ABO discrepancy is any deviation from the expected pattern of red cell antigen grouping with serum-grouping or when the forward-grouping results do not correlate with reverse-grouping results. This study was done to determine the incidence and causes of ABO discrepancies and to identify the correct blood group for safe blood transfusions.


Introduction
ABO grouping is a simple, accurate, and precise procedure and for its validity, the results of cell grouping and serum grouping should agree. In ABO blood group system, the sorting of human blood is based on the inherited properties of red blood cells as determined by the occurrence or absence of the antigens A and B, which are carried on the surface of the red cells. Persons may therefore have type A, type B, type O, or type AB blood. Blood containing red cells with type A antigen on their surface has in its serum antibodies against type B red cells 1 .
The A, B, and O blood groups were first identified by Austrian immunologist Karl Landsteiner in 1901 2 .
When the red cell antigen grouping (Forward) results do not correlate with serum grouping (Reverse), a discrepancy is said to exist. In such cases, interpretation of the ABO type must be delayed until the discrepancy is resolved 3 . In a clinical urgency, group O, Rh-compatible RBCs can be transfused until the resolution of discrepancy 4 .
There are four types of ABO discrepancies.

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Group I discrepancies comprise the unexpected reactions in the reverse grouping due to weakly reacting or missing antibodies.
• Group II discrepancies are those from unexpected reactions in forward grouping due to weakly reacting or missing antigen.
• Group III discrepancies occur due to protein or plasma abnormalities, rouleaux formation and pseudo agglutination.
• Group IV discrepancies are of a miscellaneous group and may be due to transfusion of out of group plasma containing component, presence of cold alloantibody, or autoantibody, pH dependent autoantibody, a reagent dependent antibody (e.g. EDTA, paraben) and IVIG therapy (from ABO isoagglutinins). Mix field agglutination with circulating red cell of more than one ABO type and polyagglutination (e.g. T activation) resulting from inherited or acquire. The abnormalities of red cell membrane also constitute group IV discrepancies.
ABO and Rh blood group discrepancies account for a considerable number of reported transfusion associated reactions 5 . Human errors are a major contribution to blood grouping discrepancies but some errors are not unavoidable 6,7 , but luckily, most of these errors do not lead to a critically adverse effects. Since blood transfusion is an extended and complex process linking many steps and individuals, there is possibility for a high rate of error. ABO and Rh discrepancy can thus occur 6,7,8,9. . Most of the ABO discrepancies are due to the technical error, errors in collection, errors in documentation and registration, phlebotomy errors and occasionally due to physiological problems of the patients.

Objectives
The aim of this study was to assess the ABO discrepancies which occurred during the 1 year study period and how they were handled. To the best of our knowledge, Blood types errors found on different techniques have not been published, or the subject addressed from Nepal.

Materials & Methods
All blood bank ABO typing records kept at the GIH blood bank laboratory between June 2017 to May 2018 were reviewed. The following steps were followed: • ABO and Rh typing was done which included forward cell grouping and reverse serum grouping by 2 methods i.e. tube method and gel card method done through standard operating procedure. • For A subgroup anti-A lectin was used which reacts directly with A1 and A1B but not A2 or A2B red cells.
• Ortho Bio Vue system Anti-A/Anti-B/ Anti-D Control Reverse diluents gel card for gel card grouping o All technical errors, errors in sampling, reagent errors were excluded.
o Discrepancies were solved according to discrepancy type protocol.
o Results of work-up were interpreted using a table (Grande-BB-SOP-01, page5)

Results
During 1 year, 9970 blood grouping tests were performed at Grande International Hospital (GIH). ABO discrepancies occurred 26 times with a frequency of 0.26% (1 per 384 samples). Male to female ratio was 42 to 58. The discrepancies were found to be more prevalent in the child bearing age of 20-30 years (38%) and age 30-40 (26%). Discrepancies were most commonly found in patients with a history of pregnancy/miscarriage (30%), history of carcinoma (23%), and without any significant clinical history (23 %). The most common blood group involved was B (34%), followed by A (26%), AB (23%) &O (17%). Reverse discrepancy type i.e. 96% with 84 % extra antibody was resolved by incubating the sample at 37°C for 30-60 minutes respectively signifying most probably A and B subgroups and auto/ allo antibodies.

Discussion
The study on analysis of ABO discrepancies in 35 French hospitals showed the incidence of ABO discrepancies of 1 per 3400, most of which were due to phlebotomy errors, collection from wrong patient and clerical errors -in descending order 10 . Similar study done at a University hospital in Saudi Arabia showed 261 discrepancies in 549229 samples. The most common causes were errors of blood collection during phlebotomy and clerical errors 11 .
Another genomic study on 324 clinical samples showed that the number of definable alleles associated with ABO subgroups has increased from 14 to 29 from the earlier study 12 .
Clerical errors are common and are responsible for one third of transfusion related deaths. Mixup sample, phlebotomy errors, misidentification and the technical errors were found to be common in all other studied done previously. We have excluded all these errors in this study.

Conclusion
1 per 384 discrepancies in this study emphasizes the need of considering ABO discrepancies in blood banks for donors and recipients for safe blood transfusion to avoid any fatal complications. This discrepancy ratio is more than in other studied population of other countries. This incidence is also higher than ABO mismatched transfusions at standard centers in Nepal. Repeat testing and investigating for ABO subgroups and auto/ allo antibodies is important in patients with clinical significance or without any medical history.