Blood transfusions are routine medical procedures that save lives, providing individuals with needed blood components. For a transfusion to be safe and effective, careful matching of blood types between the donor and recipient is necessary. Administering incompatible blood can lead to serious, even life-threatening, adverse reactions. Understanding these compatibility requirements is paramount to preventing complications.
Understanding Rh Factor Compatibility
Blood type classification includes the Rh factor, an inherited protein on the surface of red blood cells. Individuals are Rh-positive if their red blood cells have this Rh protein, specifically the D antigen. Those who lack the Rh D antigen are Rh-negative. Approximately 84% of the Australian population is Rh-positive, with 16% being Rh-negative. This distinction is important for transfusions, as an Rh-negative person’s immune system can recognize the Rh D antigen as foreign if exposed to Rh-positive blood.
Immediate Transfusion Reaction
When an Rh-negative person receives Rh-positive blood for the first time, their immune system identifies the Rh D antigen on the transfused red blood cells as foreign. This triggers an immune response, leading to the production of antibodies against the Rh D antigen. This initial exposure is known as sensitization, and while some antibodies may be produced, symptoms might be mild or absent. However, an acute hemolytic transfusion reaction (AHTR) can occur within 24 hours.
During an AHTR, these antibodies attack and destroy the transfused Rh-positive red blood cells, a process called hemolysis. This destruction releases free hemoglobin into the bloodstream. Common immediate symptoms include fever, chills, and pain in the abdomen, back, or flank. More severe signs can involve shortness of breath, a drop in blood pressure, and hemoglobinuria, potentially progressing to kidney failure or shock. In anesthetized patients, a sudden drop in blood pressure or evidence of disseminated intravascular coagulation (DIC) may be the first indication of a reaction.
Long-Term Implications and Future Risks
Initial exposure of an Rh-negative individual to Rh-positive blood leads to sensitization, even if the immediate reaction is mild. This means the immune system is primed and has developed memory cells against the Rh D antigen. If this individual receives Rh-positive blood again, their immune system will launch a faster, more aggressive attack. Subsequent transfusions could result in rapid, extensive red blood cell destruction, causing more pronounced and dangerous symptoms.
A significant long-term implication, particularly for Rh-negative women, involves future pregnancies. If a sensitized Rh-negative woman becomes pregnant with an Rh-positive baby, her antibodies can cross the placenta and attack the fetal red blood cells. This leads to Hemolytic Disease of the Fetus and Newborn (HDFN), also known as Rh disease, which can range from mild anemia to severe conditions like hydrops fetalis, potentially leading to fetal death. To prevent sensitization during pregnancy, Rh-negative mothers receive Rho(D) immune globulin (RhIg or RhoGAM), usually around 28 weeks of pregnancy and again within 72 hours after birth. This injection contains antibodies that bind to any Rh-positive fetal red blood cells, preventing the mother from developing her own permanent antibodies.
Preventing Incompatible Transfusions
Preventing incompatible blood transfusions relies on rigorous medical procedures and strict adherence to safety protocols. Before any transfusion, meticulous blood typing is performed, determining both the ABO blood group and the Rh factor of the recipient and the donor. This ensures major blood groups are compatible.
Following blood typing, a crucial step called cross-matching is carried out. This involves mixing a small sample of the recipient’s blood plasma with donor red blood cells to check for harmful interactions. If antibodies in the recipient’s plasma react with antigens on the donor red blood cells, it indicates an incompatibility, and the blood will not be used for transfusion. These comprehensive tests minimize the risk of adverse reactions, ensuring patients receive safe and compatible blood products.