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Blood Group System

Rh Blood Group System

The Rh blood group system includes several antigens, with the most significant being the Rh (D) antigen. This antigen is identified by the presence of a protein called Antigen-D on the surface of red blood cells. If Antigen-D is present, the blood type is classified as Rh Positive (Rh+). If Antigen-D is absent, the blood type is Rh Negative (Rh-). In the Thai population, about 99.7% are Rh+, while only around 0.3% are Rh-, which means there are approximately 3 individuals with Rh- blood in every 1,000. Thus, Rh- blood is considered “rare” or “special.”

  • Individuals with Rh+ blood can receive blood from both Rh+ and Rh- donors.
  • Individuals with Rh- blood can only receive Rh- blood.

Given its rarity, the National Blood Centre of the Thai Red Cross maintains a registry of Rh- donors. In urgent situations requiring this blood type, they can quickly locate Rh- donors to assist patients.

For patients with Rh- blood, it is crucial that they receive only Rh- blood to prevent the production of antibodies against Antigen-D. Such antibodies can lead to compatibility issues, making it increasingly difficult to find suitable blood in the future. Additionally, compatibility problems can arise between the blood of a mother and her fetus.

When providing blood to patients, it is essential to consider both the ABO blood group and the Rh factor to avoid potential complications. However, since Rh- blood is quite rare in Thailand, there is a constant demand for it, which could result in shortages.

For Rh- women who have developed Anti-D antibodies, there is a risk for fetuses that are Rh+ (like the father). The mother’s Antigen-D can cross the placenta and destroy the fetus’s red blood cells, leading to conditions such as jaundice during pregnancy and after birth.

ABO Blood Group System

The ABO blood group system is crucial and is determined by specific substances on the surface of red blood cells called antigens. There are two types of antigens: Antigen-A and Antigen-B. Each blood type also produces antibodies against the opposite blood group. For instance, a person with blood type A has Antigen-A in their red blood cells and Anti-B antibodies in their plasma.

  • Blood Type A: Individuals have Antigen-A on their red blood cells, lack Antigen-B, and produce Anti-B antibodies.
  • Blood Type B: Individuals have Antigen-B on their red blood cells, lack Antigen-A, and produce Anti-A antibodies.
  • Blood Type O: Individuals do not have either Antigen-A or Antigen-B on their red blood cells but have both Anti-A and Anti-B antibodies.

Blood Type AB: Individuals have both Antigen-A and Antigen-B on their red blood cells and do not produce either Anti-A or Anti-B antibodies.