Blood transfusion

A blood transfusion is the medical process of transferring blood products into a person's circulation intravenously. This means the blood is delivered through a tube into a vein.

Transfusions are vital for treating various medical conditions. They allow doctors to replace specific components of blood that a patient has lost. While early medicine used whole blood, modern practice usually involves specific parts of the blood. This targeted approach helps ensure patients receive exactly what their bodies need to function correctly.

Blood is composed of several distinct parts that perform different roles. Red blood cells (RBC) contain hemoglobin, which is a protein that supplies oxygen to the body's cells.

Plasma is the yellowish liquid portion of the blood. It acts as a buffer and contains proteins and other substances necessary for overall health.

Platelets are small components involved in blood clotting to prevent bleeding. White blood cells are part of the immune system and fight infections, but they are rarely used in transfusions. Modern doctors can separate these parts to treat specific issues, such as clotting deficiencies or low oxygen levels.

To create these individual parts, donated blood undergoes a process called centrifugation. During centrifugation, the blood is spun at high speeds to separate it into red blood cells, plasma, and platelets.

Plasma can even be processed further to create specific products like albumin protein or clotting factor concentrates. Some components can be donated individually through a more complex method called apheresis. Each component requires very specific storage conditions to remain safe and effective. Red blood cells are typically kept at 1–6 °C. Platelets must be stored at 20–24 °C and require continuous agitation. Plasma is stored frozen at −18 °C or even lower to preserve its clotting factors.

Safety is the most important part of the transfusion process. Before any blood is given, scientists must perform compatibility testing.

This begins by typing the recipient's blood to determine their ABO and Rh status. Scientists also screen the patient for any alloantibodies, which are antibodies that might react poorly to donor blood. This screening process takes about 45 minutes. If a patient has a history of specific antibodies, doctors must find donor cells that lack the corresponding antigens. In urgent emergencies where time is critical, doctors may use O-negative blood. This is a universal type used when the risk of waiting for a crossmatch is too high.

Testing also protects against the spread of diseases. The World Health Organization (WHO) recommends testing all donated blood for transfusion-transmissible infections. These include HIV, hepatitis B, hepatitis C, and syphilis.

Some products, like platelets, are also tested for bacterial contamination because they are stored at room temperature. In many countries, specialized filtration is used for leukocyte reduction. This process removes white blood cells to reduce the risk of transfusion reactions. Another method called pathogen reduction treatment uses riboflavin and UV light to inactivate viruses, bacteria, and parasites.

Medical decisions for transfusions are based on precise measurements. For example, red cell transfusions were historically considered when hemoglobin levels fell below 100g/L. However, modern medical evidence shows that using a lower trigger level of 70 to 80g/L leads to better patient outcomes.

For hospitalized patients who are not actively bleeding, a single unit of blood is the standard treatment. After the unit is given, doctors re-assess the patient's symptoms and hemoglobin concentration. If a patient has low hemoglobin due to iron deficiency but is stable, doctors may prefer oral or parenteral iron instead of a transfusion.

Blood can come from different sources. An autologous transfusion is when a person uses their own blood. An allogeneic transfusion is when a person receives blood from someone else, which is much more common.

In many developed countries, donations are anonymous to the recipient. However, every product in a blood bank remains individually traceable. This traceability allows for investigations if a transfusion-related disease or reaction is suspected. This rigorous system of tracking and testing connects the science of hematology to the practical reality of saving lives in hospitals every day.