Yes, plasma is in your blood. It’s actually the largest single component, making up about 55% of your total blood volume. The other 45% consists of red blood cells, white blood cells, and platelets. While those cells tend to get more attention, plasma is the liquid that carries them through your body and performs a surprising number of jobs on its own.
What Plasma Actually Is
Plasma is a pale yellow liquid that serves as the base of your blood. It’s roughly 90% water, with the remaining 10% made up of proteins (about 8%), inorganic salts (0.9%), and a small fraction of other organic substances like glucose, hormones, and dissolved gases. If you removed every cell from your blood, what you’d have left is plasma.
The three major protein types floating in plasma are albumins, globulins, and fibrinogens. Each one has a distinct role. Albumins help regulate how much water moves in and out of your blood vessels. Globulins include antibodies that fight infections. Fibrinogen is the protein responsible for blood clotting, forming a mesh-like structure at wound sites to stop bleeding.
What Plasma Does in Your Body
Plasma works as your body’s delivery and waste removal system. It carries water, hormones, nutrients, and electrolytes to the tissues and organs that need them. At the same time, it picks up waste products and routes them to your liver or kidneys for disposal.
It also plays a critical role in maintaining blood pressure. The proteins in plasma, especially albumin, help keep fluid inside your blood vessels. Without enough plasma protein, water would leak out of the bloodstream and into surrounding tissues, causing swelling. This pressure-balancing act keeps your blood vessels open and circulation moving.
One of plasma’s less obvious functions is keeping your blood at the right pH, which hovers around 7.4. It does this through a chemical buffering system involving bicarbonate ions and carbonic acid. When something acidic enters your bloodstream, bicarbonate neutralizes it. When something basic enters, carbonic acid counteracts it. This constant back-and-forth keeps your blood chemistry stable enough for your cells to function normally.
What Healthy Plasma Looks Like
Separated from blood cells, plasma is typically a clear, straw-yellow color. But it can change shades depending on what’s in a person’s system. People taking oral contraceptives sometimes have light green plasma. High doses of vitamin A, or eating large quantities of carrots, can turn plasma bright orange. These color shifts are harmless and don’t indicate a health problem.
In a lab, plasma is separated from blood cells using a centrifuge, which spins a blood sample at high speed. The heavier cells sink to the bottom of the tube, and the lighter plasma rises to the top, where it can be drawn off with a pipette. The whole process needs to happen within about an hour of the blood draw to keep the sample usable.
Plasma vs. Serum
You’ll sometimes see the terms “plasma” and “serum” used in medical contexts, and they’re not the same thing. The difference comes down to clotting factors, particularly fibrinogen. Plasma retains fibrinogen and all other clotting proteins because an anticoagulant is added to the blood sample right at collection, preventing clotting. Serum is what you get when no anticoagulant is added: the blood clots naturally, fibrinogen gets used up in the clotting process, and the remaining liquid is serum. Think of serum as plasma minus the clotting factors.
Medical Uses for Donated Plasma
Because plasma carries antibodies and clotting proteins, it has direct therapeutic value. One well-known application is convalescent plasma therapy, where plasma from someone who has recovered from an infection is transfused into a patient still fighting the same illness. The donor’s antibodies give the recipient’s immune system a boost. This approach has been used for pandemic influenza, Ebola, and Lassa virus over the years.
During the COVID-19 pandemic, convalescent plasma became a widely discussed treatment. Healthcare professionals began using it in 2020, and by December 2024, the FDA had approved convalescent plasma specifically for treating COVID-19 in people with weakened immune systems.
Beyond convalescent therapy, plasma donations are used to manufacture treatments for bleeding disorders, immune deficiencies, and burn injuries. The proteins extracted from donated plasma, especially clotting factors and immunoglobulins, are processed into concentrated therapies that many patients depend on regularly.