Blood plasma is the pale, straw-colored liquid component of blood that serves as the medium for all other blood cells to circulate throughout the body. This fluid makes up approximately 55% of the total blood volume. Plasma is primarily composed of water (about 92% by volume) but also contains dissolved substances, including proteins, electrolytes, hormones, and nutrients. Extracting this fluid is necessary for diagnostic testing, manufacturing medicines, and providing direct patient therapies.
The Principle of Plasma Separation
The most common method used to separate plasma from whole blood relies on the physical principle of differential density. This process, known as centrifugation, subjects a sample of whole blood to a high-speed spinning force that amplifies gravity. Since blood components possess distinct densities, the centrifugal force causes them to separate into visible layers within a collection tube.
When blood treated with an anticoagulant is spun, the heaviest components are forced to the bottom. Red blood cells, which have the highest density, form the lowest and largest layer. Plasma, the least dense component, remains at the very top.
A thin, whitish layer called the buffy coat forms between the red blood cells and the plasma. This intermediate layer contains the white blood cells and platelets. In a laboratory setting, spinning the sample is sufficient to achieve clean separation, allowing the plasma to be drawn off for subsequent use.
Clinical Plasmapheresis and Donation
For high-volume collection needed for therapeutic manufacturing or donation, the separation process is automated using a procedure called plasmapheresis. This method continuously draws blood from the donor, separates the plasma, and returns the remaining blood components in a cycle. Returning the red blood cells, white blood cells, and platelets allows for a much larger volume of plasma to be collected than a traditional whole blood donation.
The apheresis machine uses a sterile, single-use kit connected to the donor’s vein. Inside the machine, a centrifuge or filtration system separates the plasma from the cellular components based on density. The device collects the plasma into a separate bag while mixing the remaining blood components with a saline solution for reinfusion.
Because the donor’s red blood cells are returned, the body can quickly replace the fluid volume removed, enabling donors to participate more frequently than with whole blood donation. A typical plasma donation session takes between 45 and 90 minutes. This automated process makes it possible to collect up to a liter of plasma in a single sitting.
Essential Applications of Plasma Products
The extracted plasma is utilized in two primary ways: direct transfusion and industrial fractionation. Direct transfusion involves quickly freezing the collected plasma to create Fresh Frozen Plasma (FFP). FFP is administered to patients experiencing blood loss, trauma, or liver failure to replace clotting factors necessary for proper hemostasis.
The majority of donated plasma is sent for fractionation, a manufacturing process that isolates and purifies specific proteins. This process yields specialized medications that treat a variety of conditions. Immunoglobulins, for example, are extracted and concentrated for use in patients with compromised immune systems or autoimmune disorders.
Other proteins purified through fractionation include albumin, which is used to treat burn victims and patients in shock by helping to maintain fluid volume. Clotting factors, such as those used to treat hemophilia, are also separated and concentrated from large pools of plasma. These medications manage congenital deficiencies and life-threatening conditions.