Whole blood is a complex fluid tissue that carries out functions from gas exchange to immune defense. This mixture is rarely used in its entirety for modern medical treatment. Instead, advanced processing techniques are used to separate whole blood into its constituent parts, a process known as fractionation. Fractionation allows healthcare providers to isolate specific components, creating specialized therapeutic products to treat a wide variety of medical conditions.
The Major Components of Whole Blood
Whole blood separates into four primary components: red blood cells, white blood cells, platelets, and plasma. Red blood cells (erythrocytes) are the most numerous cellular component and transport oxygen using hemoglobin.
White blood cells (leukocytes) form the body’s mobile defense system, playing a central role in the immune response. Platelets (thrombocytes) are small cell fragments that initiate the clotting cascade to prevent blood loss. The remaining volume is plasma, a straw-colored liquid that makes up about 55% of the total blood volume. Plasma is primarily water, carrying essential proteins, hormones, nutrients, and electrolytes throughout the body.
Isolation Techniques: How Blood is Separated
The initial separation of whole blood into its major components is most commonly achieved through centrifugation. This method applies high-speed rotational force to a blood sample, separating components based on density. Red blood cells settle at the bottom, plasma rises to the top, and platelets and white blood cells form the intermediary buffy coat.
Another technique, called apheresis, allows for the collection of a single, targeted component directly from a donor. A machine draws whole blood, uses a centrifuge to separate the desired element (such as platelets or plasma), and then returns the remaining components to the donor. This method allows for the collection of a therapeutic dose of a single component in one session.
Understanding Plasma Derivatives
The term “blood fractionation” is often used specifically to describe the further breakdown of plasma into therapeutic protein concentrates, or plasma derivatives. While plasma contains thousands of proteins, only a handful are isolated for large-scale medical use.
The foundational technique for this deep separation is the Cohn cold ethanol process, developed in the 1940s. This method uses precise adjustments of temperature, pH, and ethanol concentration to sequentially precipitate different proteins based on their solubility, enabling industrial-scale purification.
Key Plasma Derivatives
Albumin: Used to restore blood volume and maintain oncotic pressure in patients experiencing shock or severe burns.
Immunoglobulins: Purified antibodies used to treat patients with compromised immune systems or to provide passive immunity.
Clotting Factors: Concentrated proteins, such as Factor VIII, used to manage bleeding disorders like hemophilia A.
Clinical Applications of Blood Fractions
The ability to separate blood into specialized fractions allows clinicians to provide targeted treatment for various medical conditions. Packed red blood cells are routinely transfused to patients suffering from significant blood loss due to trauma, surgery, or severe anemia.
Platelet concentrates are administered to patients with low platelet counts, such as those undergoing chemotherapy, to prevent excessive bleeding. Plasma derivatives offer highly concentrated therapeutic solutions not possible with whole blood. Albumin is used to rapidly expand blood volume, while immunoglobulins provide immediate protection against infections or modify autoimmune responses. Clotting factor concentrates ensure that patients with hemophilia have the necessary proteins to form stable blood clots. Specialized component therapy provides targeted treatment, underscoring its value over the transfusion of whole blood.