Immuno haematology: Blood Group Systems and Transfusion Science

Immunohaematology is the branch of haematology that deals with the study of blood groups, blood transfusion, and immune-related reactions to transfused blood.

The ABO and Rh blood group systems are the most significant among the numerous blood group systems known today.

I. ABO Blood Group System

The ABO blood group system classifies blood into four groups based on the presence or absence of two antigens, A and B, on red blood cells:

Blood Group A: Contains A antigen and anti-B antibodies.
Blood Group B: Contains B antigen and anti-A antibodies.
Blood Group AB: Contains both A and B antigens, but no antibodies.
Blood Group O: Contains neither A nor B antigens but has both anti-A and anti-B antibodies.

H Antigen and Bombay Blood Group

The H antigen is a precursor for A and B antigens and is present in all blood groups. However, a rare variation called the Bombay blood group (Oh) was discovered in 1952 by Bhende et al.

Individuals with this group lack A, B, and H antigens, and their serum contains anti-A, anti-B, and anti-H antibodies. They can only receive blood from other Bombay blood group individuals.

II. Rh Blood Group System

The Rh blood group system was identified by Landsteiner and Wiener. The Rh factor, particularly the D antigen, determines whether a person is Rh-positive or Rh-negative. Approximately 93% of Indians are Rh-positive, while 7% are Rh-negative.

Unlike the ABO system, natural Rh antibodies are absent. Rh antibodies develop only after exposure to Rh-positive blood through transfusion or pregnancy. The Coombs test is used to detect Rh antibodies in maternal and neonatal blood.

Also Read: ELISA Technique in Microbiology

III. Haemolytic Disease of the Newborn (HDN)

HDN occurs when an Rh-negative mother carries an Rh-positive fetus. During delivery, fetal blood enters the mother’s circulation, leading to antibody production.

In subsequent pregnancies, maternal Rh antibodies cross the placenta, attacking fetal red blood cells, leading to erythroblastosis fetalis or hydrops fetalis.

Prevention of HDN

HDN can be prevented by administering anti-Rh IgG (Rh immunoglobulin) immediately after the first delivery to block the immune response and prevent sensitization.

ABO Haemolytic Disease

ABO haemolytic disease occurs when an O blood group mother has an A or B group fetus. Unlike Rh disease, ABO HDN can occur in the first pregnancy because O group mothers produce IgG antibodies, which can cross the placenta. However, this disease is usually milder than Rh HDN.

IV. Complications of Blood Transfusion

Blood transfusion complications can be immunological or non-immunological.

1. Immunological Complications

Haemolytic reactions: Occur due to blood group incompatibility, leading to red cell destruction.
Allergic reactions: Manifest as fever, urticaria, and anaphylaxis due to hypersensitivity to donor proteins.

2. Non-Immunological Complications

Transmission of Infectious Diseases: Includes viruses (HIV, Hepatitis B and C, CMV), bacteria (Treponema pallidum, Leptospira interrogans), and protozoa (Plasmodium, Leishmania donovani, Toxoplasma gondii).
Iron Overload: Frequent transfusions can lead to excessive iron accumulation, causing organ damage.

Conclusion

Immunohaematology plays a vital role in blood transfusion safety and disease prevention. Understanding the ABO and Rh systems, along with transfusion risks, is crucial for ensuring compatible and safe blood transfusions. Research continues to enhance transfusion medicine, aiming for improved patient outcomes.