Blood plasma is the pale yellow liquid that carries your blood cells through your body. It makes up about 55% of your total blood volume, with the remaining 45% consisting of red blood cells, white blood cells, and platelets. Despite being mostly water, plasma is packed with proteins, nutrients, hormones, and waste products that keep nearly every system in your body functioning.
What Plasma Is Made Of
Plasma is roughly 90% water. The remaining 10% is a complex mix of dissolved substances: proteins, salts (electrolytes like sodium and potassium), glucose, fats, hormones, vitamins, dissolved gases, and metabolic waste products your body needs to filter out. That 10% does a remarkable amount of work.
The proteins in plasma are the most functionally important component. They fall into three main categories:
- Albumin is the most abundant plasma protein. It acts like a sponge that holds water inside your blood vessels by maintaining what’s called oncotic pressure, about 25 to 28 mmHg of force across capillary walls. Without enough albumin, fluid leaks into surrounding tissues and causes swelling. Albumin also works as a transport vehicle, ferrying hormones, fatty acids, and medications throughout the body.
- Globulins include the immunoglobulins, which are your antibodies. These proteins recognize and fight off bacteria, viruses, fungi, and parasites. Other globulins help transport metals and fat-soluble vitamins in the bloodstream.
- Fibrinogen is the protein responsible for blood clotting. When you cut yourself, fibrinogen converts into fibrin strands that form a mesh over the wound. Fibrinogen levels also rise during inflammation, which is why doctors sometimes use related blood tests as a marker for infection or inflammatory disease.
What Plasma Does in Your Body
Plasma’s most obvious job is transportation. It carries oxygen and carbon dioxide (dissolved in the liquid, separate from what red blood cells carry), delivers glucose and amino acids to cells, and hauls metabolic waste to the kidneys and liver for removal. Hormones released by glands travel through plasma to reach their target organs. Fat-soluble substances that can’t dissolve easily in water hitch a ride on plasma proteins, particularly albumin.
Plasma also plays a critical role in maintaining blood pressure and fluid balance. The proteins dissolved in plasma create an osmotic pull that keeps water from leaving the bloodstream and flooding into tissues. Most capillary walls are too small for plasma proteins to pass through, so those proteins stay inside the vessels and hold fluid in place. When albumin levels drop, as they can in liver disease or severe malnutrition, the result is often visible swelling in the legs or abdomen.
Beyond transport and fluid balance, plasma proteins contribute about 7% of your blood’s total buffering capacity, helping keep blood pH in the narrow range (7.35 to 7.45) that your cells need to function. And fibrinogen, along with other clotting factors dissolved in plasma, stands ready to seal damaged blood vessels within seconds of an injury.
Plasma vs. Serum
These two terms come up frequently in lab work, and the difference is straightforward. Plasma is what you get when you prevent blood from clotting (by adding an anticoagulant) and then spin out the cells. Serum is what you get when you let blood clot first, then remove the clot and cells. The key distinction: serum lacks fibrinogen and other clotting factors because those proteins were used up forming the clot.
In clinical labs, serum is often the preferred sample for metabolic testing because it requires no additives that might interfere with measurements. Plasma is preferred when clotting factors themselves need to be measured, or when a lab needs to process samples quickly since you don’t have to wait for clotting to finish.
Medical Products Made From Plasma
Donated plasma is the raw material for a range of life-saving treatments. Pharmaceutical companies fractionate plasma (separate it into its component proteins) to produce specific therapies. The major ones include albumin solutions used to treat burns, shock, and liver failure; immunoglobulin infusions that provide antibodies to people with immune deficiencies or certain autoimmune conditions; and concentrated clotting factors for people with hemophilia. Prothrombin complex concentrates and antithrombin are also derived from plasma and used in emergency situations involving uncontrolled bleeding or clotting disorders.
These products cannot be synthesized artificially at scale, which is why plasma donation remains essential. Unlike whole blood donation, plasma donation uses a process that separates the plasma from your blood cells and returns those cells to your body during the same session.
How Quickly Plasma Regenerates
Your body replaces plasma faster than any other blood component. With proper hydration, your blood volume returns to normal within about 48 hours after a donation. This is largely because the water and salt portion of plasma is easy for your body to replenish from the fluids you drink. The protein component takes a bit longer to fully restore, since your liver needs to manufacture replacement albumin, globulins, and fibrinogen, but the overall volume recovery is remarkably fast. This rapid turnaround is why plasma donors can give more frequently than whole blood donors.