Transfusion Medicine

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    Prevalence of unexpected red cell antibodies in healthy donor population in a tertiary care center in south kerala
    (SCTIMST, 2019-12) Gayathri A M
    Naturally occurring anti-A and anti-B are the only red cell antibodies that are commonly found in human serum or plasma. All other antibodies are called “unexpected red cell antibodies [1]. There are two types of unexpected red cell antibodies: alloantibodies and auto-antibodies. Alloimmunization occurs because of red cells antigenic differences between donor and recipient in previous transfusions or between mother and fetus. Auto-antibodies are those produced against one’s own antigens. Immune humoral response in the presence of autoantibodies against intracellular antigens characteristically occurs in a majority of connective tissue diseases namely systemic lupus erythematous, systemic sclerosis, Sjögren syndrome, mixed connective tissue disease, polymyositis, and dermatomyositis [2]. Presence of these antibodies, alone or in combination, makes difficulties with compatibility testing, thereby delaying in issue of a compatible blood unit or may reduce post transfusion RBC life span [3]. The compatibility test comprises ABO/Rh determination, antibody screen and cross-match. Type & cross-match technique/Immediate spin cross match is routinely practised now which only detects ABO incompatibility between donor RBCs and recipient serum/plasma. Type & screen method is performed only when the recipient has unexpected alloantibodies to detect additional RBC incompatibility [4]. Because of the presence of auto-antibodies, all crossmatches become incompatible. Studies conducted based on these unexpected antibodies have largely concentrated on multiply transfused patient populations or antenatal women. Alloimmunization in these groups has a reported incidence up to 60 percent, with an up to fourfold increased risk of multiple antibodies compared to the risk of single antibodies [5]. However, such studies related to healthy donor population are not done extensively. The incidence of RBC alloimmunization depends on the demography and characteristics of the population being studied. The specificity, Ig class, thermal range and concentration of the antibody can predict its clinical significance as well as patient’s individual immune response is also significant factors. The balance between sensitivity and specificity can be influenced by the methods and technologies selected. It is not possible to detect all potentially clinically significant antibodies, or to avoid detecting all clinically insignificant antibodies [6]. The Direct Antiglobulin test (DAT) is a simple test used to determine if red cells have been coated in vivo with immunoglobulin (Ig), complement or both. It is used primarily for the investigation of hemolytic transfusion reactions, haemolytic disease of the fetus and newborn (HDFN), autoimmune hemolytic anemia (AIHA), and drug-induced immune hemolysis. An indirect antiglobulin test (IAT) is used to detect and identify unexpected antibodies in the serum of blood donors, prospective transfusion recipients, and prenatal patients [7]. IAT detect in vitro antibody-antigen reactions and detect very low concentrations of antibodies present in an individual’s plasma/serum. When unexpected antibodies are present, as indicated by positive screening tests, they must be identified. At a minimum, this involves testing the patient’s serum against a panel of fully phenotyped reagent red cell samples as well as the patient’s own cells [6]. A recent study suggests that a positive DAT result in a healthy blood donor may be a marker of risk of future development of malignancy [8]. All these point towards the need of Type & Screening system to be followed routinely in transfusion practices rather than Type & Matching system. Antibody screening is mandatory as laid down by Drug and Cosmetic Act 1940 and Directorate General of Health Services (DGHS) guidelines. Hence through this thesis work, we are implementing routine antibody screening along with DAT testing in every donated units in our Institute. Our donor pool consists of 100% voluntary regular donors who are considered to be absolutely safe and almost free of any infections and highly motivated. This study also helps to find the prevalence of irregular antibodies in such healthy donors there by aiding best transfusion practices to be followed in the institution since there is scarce data available on prevalence and type of irregular antibodies in Indian donor population.
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