Blood is composed of several distinct components, including plasma, platelets, and various types of blood cells. When a patient requires a transfusion, medical practice generally focuses on providing only the specific component that is needed. Among these separated products, Packed Red Blood Cells (PRBCs) represent the most frequently transfused component globally. PRBCs play a fundamental role in modern healthcare by directly addressing the body’s capacity to transport oxygen.
What PRBCs Are and How They Are Prepared
Packed Red Blood Cells are a specialized blood product consisting primarily of concentrated red blood cells (RBCs) with most of the plasma, platelets, and white blood cells removed. The goal is to provide a high concentration of oxygen-carrying cells in a reduced volume of fluid. A typical unit of PRBCs contains a hematocrit, or volume percentage of red cells, ranging from approximately 55% to 70%.
Preparation begins with the collection of whole blood from a donor into a bag containing an anticoagulant solution, such as citrate-phosphate-dextrose (CPD). The whole blood is then subjected to centrifugation, where it is spun at high speed to separate the components based on density. Red blood cells are the densest components, settling to the bottom of the collection bag.
The supernatant layers, including the plasma and the buffy coat containing platelets and most white blood cells, are then carefully removed. An additive solution is introduced to the remaining red cells to provide nutrients and preserve cell viability. This process yields the final PRBC product, which provides a significant mass of hemoglobin in a small volume, typically between 250 to 320 milliliters per unit.
Why PRBCs Are Used in Medicine
The primary purpose of transfusing PRBCs is to restore or improve the oxygen-carrying capacity of the blood, preventing tissue hypoxia, or oxygen deprivation. Red blood cells contain hemoglobin, the protein responsible for binding and transporting oxygen from the lungs to every tissue in the body. When the red cell mass is insufficient, the body’s oxygen supply is compromised.
The most common indication for PRBC transfusion is the treatment of symptomatic anemia, where a patient experiences symptoms like fatigue, dizziness, shortness of breath, or chest pain. While the clinical decision is not based on a single number, a general guideline for stable, non-bleeding adults is a hemoglobin level below 7 g/dL. This threshold may be higher, around 8 g/dL, for patients with pre-existing cardiovascular conditions or those undergoing orthopedic surgery.
PRBCs are also used to replace red cell mass following significant acute blood loss, such as from major trauma or complex surgery. Acute hemorrhage can lead to hemodynamic instability and shock, requiring rapid replacement of lost cells. Patients with chronic conditions, including kidney failure, certain cancers, or inherited disorders like sickle cell disease, may require regular transfusions. The administration of one unit of PRBCs typically raises the hemoglobin concentration in an average-sized adult by approximately 1 g/dL.
PRBCs Versus Whole Blood
The key distinction between PRBCs and whole blood (WB) lies in their composition and concentration. Whole blood contains all original components—red cells, plasma, and platelets—and is therefore more dilute than PRBCs. PRBCs, by contrast, are a concentrated product with most of the plasma removed.
The widespread use of PRBCs is part of component therapy, which allows clinicians to give patients only the specific blood component they are lacking. This approach prevents unnecessary exposure to other blood components, reducing the risk of certain adverse reactions. The concentrated nature of PRBCs minimizes the volume transfused, which is important for patients at risk of fluid overload, known as Transfusion-Associated Circulatory Overload (TACO).
Whole blood is rarely used in routine civilian medicine and is generally reserved for situations of massive, rapid hemorrhage, often seen in military or acute trauma settings. In these scenarios, the simultaneous replacement of clotting factors and volume provided by whole blood may offer a survival advantage. PRBCs remain the standard of care for correcting anemia and addressing most acute blood loss in a controlled hospital environment.
Shelf Life and Transfusion Safety
PRBC units are subject to strict storage and handling protocols to maintain their efficacy and ensure patient safety. They are stored under constant refrigeration at a temperature range of 1°C to 6°C. The addition of preservative solutions, such as those containing adenine, glucose, and mannitol, allows the red cells to be stored for up to 42 days while preserving their function.
Before a transfusion is administered, several safety procedures are mandatory to prevent potentially severe adverse reactions. The patient’s blood must first be typed to determine the ABO and Rh status, followed by cross-matching with the donor unit. Cross-matching confirms compatibility between the patient’s plasma and the donor’s red cells, which is necessary to avoid an acute hemolytic reaction.
Patients are monitored for acute transfusion reactions, which can include fever or allergic responses. Modern blood banking practices often include leukoreduction, a process that filters out most white blood cells from the PRBC unit. Leukoreduction reduces the risk of febrile non-hemolytic transfusion reactions and the transmission of certain viruses. Proper handling and administration, including completing the transfusion within a four-hour window, are necessary to ensure the therapeutic benefit and safety of the product.