Prevalence of unexpected red cell antibodies in healthy donor population in a tertiary care center in south kerala
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Date
2019-12
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SCTIMST
Abstract
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.