Plasma is the liquid portion of your blood. 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 its simple appearance as a pale yellow fluid, plasma performs a surprising range of jobs, from transporting nutrients to fighting infections to helping your blood clot when you’re injured.
What Plasma Is Made Of
Plasma is mostly water, about 91% to 92%. The remaining 8% to 9% is a mix of dissolved solids: proteins, salts, sugars, fats, hormones, and waste products your body needs to move from one place to another. That small percentage of solids is what makes plasma so functionally important.
The three major protein groups in plasma are albumin, globulins, and fibrinogen. Albumin is the most abundant and acts like a sponge, holding water inside your blood vessels so fluid doesn’t leak into surrounding tissues. It also serves as a carrier molecule, binding to hormones, fatty acids, and medications to shuttle them through the bloodstream. Globulins include antibodies (the proteins your immune system produces to fight infections) along with other proteins that transport metals like iron and copper. Fibrinogen is the protein responsible for blood clotting. When you cut yourself, fibrinogen converts into fibrin threads that form a mesh over the wound.
Beyond proteins, plasma carries electrolytes like sodium, potassium, and calcium that keep your muscles, nerves, and heart functioning properly. It also contains dissolved gases, glucose for energy, and metabolic waste products like urea that are being ferried to the kidneys or liver for removal.
What Plasma Does in Your Body
Plasma is essentially your body’s delivery and waste-removal system. Every cell in your body depends on plasma to bring it nutrients and oxygen and to carry away what it no longer needs. Carbon dioxide, for example, is absorbed from cells by plasma and transported back to the lungs, where you exhale it. Some of that carbon dioxide also binds to hemoglobin inside red blood cells, but plasma handles a significant share of the work.
Hormones produced by glands throughout your body travel through plasma to reach their target organs. Insulin released by the pancreas, thyroid hormones, cortisol: all of these ride the plasma current to wherever they’re needed. Plasma also distributes heat evenly throughout your body, helping maintain a stable internal temperature.
One of plasma’s less obvious roles is maintaining blood pH. Your blood stays in a narrow range of 7.35 to 7.45, and even small shifts outside that window can be dangerous. Plasma contains a bicarbonate buffering system that neutralizes excess acid or base. When carbon dioxide dissolves in plasma, it forms carbonic acid, which can then release or absorb hydrogen ions depending on what the body needs. Your lungs help regulate this by breathing out more or less carbon dioxide, and your kidneys fine-tune it by adjusting how much bicarbonate they retain. This system keeps your blood chemistry remarkably stable even during exercise, illness, or changes in diet.
Plasma vs. Serum
You’ll sometimes see “plasma” and “serum” used in medical contexts, and they’re closely related but not the same thing. Plasma is what you get when you separate the liquid from whole blood using a spinning machine (a centrifuge) while preventing the blood from clotting. Serum is what’s left over after blood has been allowed to clot and the clot is removed. The key difference: plasma still contains fibrinogen and other clotting factors, while serum does not. Doctors choose one over the other depending on what lab test they’re running.
Medical Uses of Donated Plasma
Plasma donation saves lives in ways that whole blood donation cannot. Because plasma is rich in clotting factors and antibodies, it’s used to treat a wide variety of conditions, from emergency trauma to chronic genetic diseases.
Trauma patients and burn victims receive plasma transfusions to help their blood clot and to restore blood volume, which prevents shock. But the majority of donated plasma goes toward manufacturing specific therapies. Proteins are extracted from pooled plasma donations and concentrated into treatments for people with immune deficiencies, bleeding disorders, lung diseases, and autoimmune conditions. People with hemophilia, for instance, rely on clotting factors derived from plasma. Those with primary immunodeficiency receive antibody infusions made from donated plasma to compensate for an immune system that can’t produce enough on its own.
The scale of plasma needed for these therapies is striking. Treating one person with primary immunodeficiency for a single year requires about 130 plasma donations. Someone with hemophilia needs roughly 1,200 donations per year. A person with alpha-1 antitrypsin deficiency, a genetic condition affecting the lungs, requires around 900 donations annually. These numbers illustrate why plasma collection centers operate year-round and why demand consistently outpaces supply.
Plasma-derived antibodies also treat specific infections. People exposed to tetanus who haven’t been vaccinated can receive antibodies harvested from the plasma of vaccinated donors, sometimes as the only available treatment. Similar antibody therapies exist for rabies exposure. Pregnant individuals with Rh sensitization, a condition where the mother’s immune system attacks the baby’s blood cells, receive plasma-based treatments to protect the fetus from brain damage or death.
How Plasma Donation Works
Donating plasma is different from donating whole blood. In a process called plasmapheresis, blood is drawn from your arm, run through a machine that separates the plasma from the blood cells, and then the blood cells are returned to your body along with saline. The whole process typically takes longer than a standard blood draw, usually 60 to 90 minutes.
Because your body replaces plasma faster than it replaces red blood cells, you can donate plasma more frequently than whole blood. Current guidelines allow donation once every two days, with a maximum of twice per seven-day period. Your body replenishes the lost plasma within about 24 to 48 hours, though the proteins in it take a bit longer to fully restore.