Plasma is the liquid portion of your blood. It makes up about 55% of your total blood volume and serves as the river that carries red blood cells, white blood cells, and platelets throughout your body. When you donate plasma, a machine draws your blood, separates out this straw-colored liquid, and returns your blood cells back to you. The plasma you give is then used to manufacture medications and therapies for people with immune deficiencies, bleeding disorders, burns, and other serious conditions.
What Plasma Actually Is
Plasma is roughly 90% water. The remaining 10% is what makes it medically valuable: a concentrated mix of proteins, salts, hormones, and lipids. The most abundant protein is albumin, which keeps fluid from leaking out of your blood vessels and into surrounding tissues. Albumin is responsible for about 80% of the pressure that holds fluid inside your capillaries. It also acts as a transport vehicle, carrying fatty acids, trace minerals, and certain medications through the bloodstream.
Beyond albumin, plasma contains immunoglobulins, which are antibodies your immune system produces to fight bacteria, viruses, and toxins. There are several types, each with a different job. Some coat invading bacteria so your immune cells can destroy them more easily. Others line the surfaces of your respiratory and digestive tracts, catching pathogens before they can take hold. One type even crosses the placenta during pregnancy to give newborns temporary immunity.
Plasma also carries clotting factors, the proteins that stop bleeding when you get a cut. Fibrinogen is the most well-known of these. When a blood vessel is damaged, fibrinogen converts into long, sticky threads that form a mesh over the wound. Other clotting proteins in plasma exist in inactive forms, ready to activate in a cascade when needed. People with hemophilia and other bleeding disorders lack some of these factors, which is one reason donated plasma is so critical.
Why Donated Plasma Is Valuable
Most donated plasma goes to pharmaceutical companies that fractionate it, meaning they break it down into its individual protein components. These components become specific therapies. Immunoglobulin products, for instance, are concentrated antibodies given to people whose immune systems can’t produce enough on their own. Clotting factor concentrates go to patients with hemophilia. Albumin solutions are used in hospitals to treat severe burns, liver failure, and shock.
Some plasma is also frozen shortly after collection and stored as fresh frozen plasma (FFP), which can be transfused directly into patients who need rapid replacement of multiple clotting factors at once, such as during major surgery or massive blood loss. Frozen plasma stays usable for up to 24 months when stored at minus 25°C or colder.
How the Donation Process Works
Plasma donation uses a process called plasmapheresis, which is different from a standard blood draw. A needle is placed in your arm, and blood flows into a machine that separates plasma from blood cells. The separation happens one of two ways: the machine either spins your blood in a centrifuge, using centrifugal force to push the heavier cells to the outside while the lighter plasma stays in the center, or it passes blood through a bundle of hollow fiber membranes with tiny pores. These pores are large enough to let plasma through but too small for blood cells, which range from 1 to 25 micrometers in diameter.
Once the plasma is collected, the machine returns your red blood cells, white blood cells, and platelets back into your arm along with a small amount of saline. This return cycle is why plasmapheresis takes longer than a regular blood donation, typically 60 to 90 minutes. It’s also why you can donate plasma more frequently than whole blood: you’re keeping your cells, so recovery is faster.
How Much Plasma Is Collected
The volume collected depends on your body weight. The FDA sets specific limits:
- 110 to 149 pounds: up to 625 mL of plasma per session
- 150 to 174 pounds: up to 750 mL per session
- 175 pounds and above: up to 800 mL per session
For reference, 800 mL is a little less than a quart. These weight-based limits exist because a larger body has a greater total blood volume and can safely spare more plasma at one time. Most donation centers in the U.S. allow two donations per seven-day period, with at least one day between visits.
What Happens to Your Body Afterward
Your body begins replacing the donated plasma almost immediately. The fluid volume, which is mostly water and salts, is typically restored within 24 hours as long as you drink extra fluids. The protein component takes a bit longer. Your liver manufactures albumin, clotting factors, and other plasma proteins continuously, and most donors see their levels return to normal within 48 to 72 hours.
Because your red blood cells are returned to you during donation, you don’t experience the same drop in oxygen-carrying capacity that comes with whole blood donation. This is why the recovery window is shorter and repeat donations are permitted more frequently. Still, staying well-hydrated and eating protein-rich meals before and after a session helps your body rebuild its plasma protein supply efficiently.
Eligibility Requirements
Plasma donors in the U.S. must pass a medical exam and an extensive screening process before their first donation. This includes testing negative for hepatitis and HIV, providing identification and proof of address, and answering a detailed health questionnaire. At each subsequent visit, staff check your vital signs and may test a small blood sample to ensure you’re healthy enough to donate that day. Weight minimums typically start at 110 pounds, since the FDA’s volume guidelines don’t cover anyone lighter than that. Age requirements vary by center but generally range from 18 to 69.