What is RBCs
Red blood cells (RBCs) are also known as erythrocytes. The functions of red blood cells are to deliver oxygen from the lungs to tissues and carry waste products, such as carbon dioxide, to the lungs for exhalation. Red blood cells (RBCs) can carry oxygen because they possess hemoglobin, a protein that binds to oxygen and facilitates its transport throughout the body. RBCs are developed in the bone marrow. The very first stage of RBC development is the transformation of a hemocytoblast, a stem cell in the bone marrow, into an erythroblast, a cell that synthesizes hemoglobin; second, as the erythroblast fills with hemoglobin, both nucleus and mitochondria will disappear; last, after 7 days maturation, it becomes reticulocyte, a mature RBC. Since mature RBCs do not contain a nucleus, they become more flexible to move in human body tissue and have a biconcave shape. Moreover, the life span of a red blood cell is from 100 to 120 days.
What is the hemolysis reaction
Hemolysis reaction, or hemolytic transfusion reaction (HTR), is the destruction process of red blood cells. It occurs when the red blood cells given during the transfusion were destroyed by one’s immune system. Blood-related factors differ among people, including ABO and Rh. To further explain, bloods that contain Rh factors are called Rh positive, while bloods without Rh factors are called Rh negative. Due to structural differences (with or without protein on the surface), antibodies against Rh factors would be formed when Rh negative people receive Rh positive blood. Similarly, speaking of ABO blood group, individuals tend to produce antibodies against antigens absent on their RBC surfaces; for instance, people with blood type A make antibodies to B and vice versa. That said, when incompatible blood groups meet, the immune system of the blood recipient would attack and destroy the donated blood cells.
Hemolysis reactions can occur in both intravascular and extravascular spaces, in circulation and in the reticuloendothelial system respectively. Intravascular hemolysis happens when an antibody that activates complement activation attaches to an RBC antigen. On the other hand, extravascular hemolysis takes place when an antibody that targets an RBC antigen opsonizes the RBC, causing it to be sequestered and phagocytosed by macrophages, dendritic cells, and neutrophils.
While hemolytic reactions can react acutely (within 24 hours of transfusion), a delayed reaction is possible as well, which usually occurs in the range of 2 weeks to 30 days post-transfusion.
Introduction to Rh blood system
The Rh blood group system is one of the most significant blood group systems, second only to the ABO system in importance. It includes numerous antigens, with the most notable being the RhD antigen, which determines whether blood is classified as Rh-positive or Rh-negative. Discovered in 1940, the Rh system plays a critical role in blood transfusions and pregnancy. An incompatibility between a Rh-negative mother and Rh-positive fetus can lead to hemolytic disease of the newborn, a potentially serious condition. The Rh system's complexity arises from the presence of over 50 antigens, primarily located on the RHD and RHCE genes. Understanding Rh typing is essential in clinical settings to prevent adverse transfusion reactions and manage pregnancies at risk of Rh incompatibility. Regular screening for Rh status is standard practice in prenatal care and blood donation.
Rh negative blood shortage issues
The shortage of Rh-negative blood has become a critical issue, with health authorities issuing urgent appeals for donations. Rh-negative blood, found in only about 1.5% of the population, is particularly vital for emergency situations and in treating women of childbearing age. The NHS in the UK has declared a national alert, stating that national stocks of O-negative and O-positive blood have fallen to "unprecedentedly low levels" due to increased hospital demand and a significant drop in donor appointments. Washington State in the U.S. is also facing dangerously low supplies, especially for O and Rh-negative types, attributed to the lingering effects of the COVID-19 pandemic on donor participation. Transfusing RhD-positive blood to RhD-negative patients carries significant risks, primarily related to the potential for alloimmunization. Studies indicate that there is a minimum 20% risk of alloimmunization when RhD-negative patients receive RhD-positive red blood cells. This can lead to the development of anti-D antibodies, which may complicate future transfusions and pregnancies. Alloimmunization can result in significant clinical implications, including delayed transfusion compatibility and increased risk of hemolytic reactions in future transfusions. Patients who become sensitized may require RhD-negative blood for all future transfusions, which can be challenging during shortages. For RhD-negative women of childbearing age, the presence of anti-D antibodies poses a risk of hemolytic disease of the fetus and newborn (HDFN) in subsequent pregnancies.
References
Chérif-Zahar B;Bony V;Steffensen R;Gane P;Raynal V;Goosens D;Laursen JS;Varming K;Jersild C;Cartron JP;, B, et al. “Shift from Rh-Positive to Rh-Negative Phenotype Caused by a Somatic Mutation within the RHD Gene in a Patient with Chronic Myelocytic Leukaemia.” British Journal of Haematology, U.S. National Library of Medicine, Sept. 1998, pubmed.ncbi.nlm.nih.gov/9753055/.
