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 being easy to overlook next to those more familiar blood cells, plasma is what keeps everything moving, dissolved, and in balance throughout your body.
The word “plasma” also refers to something completely different in physics: a state of matter. Both meanings come up frequently, so this article covers both, starting with the one most people are searching for.
What Blood Plasma Is Made Of
Plasma is mostly water, about 91% to 92% by volume. The remaining 8% to 9% is a mix of dissolved solids: proteins, electrolytes (salts like sodium and potassium), nutrients like glucose, hormones, waste products, and dissolved gases like oxygen and carbon dioxide. It has a pale yellow color, which you can see if blood is spun in a centrifuge to separate the cells from the liquid.
The proteins in plasma do most of the heavy lifting. The three major types are albumin, globulins, and fibrinogen, and each serves a distinct purpose. Albumin is the most abundant. It acts like a sponge, pulling water into blood vessels to maintain the right fluid balance and preventing tissues from swelling. Globulins include antibodies that fight infections, along with proteins that transport fats and vitamins through the bloodstream. Fibrinogen is the protein responsible for blood clotting. When you get a cut, fibrinogen converts into fibrin threads that form a mesh over the wound.
The electrolytes dissolved in plasma are tightly regulated. Normal sodium levels fall between 135 and 145 milliequivalents per liter, while potassium sits between 3.5 and 5. Even small shifts outside these ranges can cause serious problems with nerve signaling, muscle contraction, and heart rhythm, which is why the body works hard to keep them stable.
What Plasma Does in Your Body
Plasma serves as the body’s transportation network. Every hormone released by a gland, every nutrient absorbed from food, and every waste product headed for the kidneys travels through plasma. Without it, none of the chemical signals your organs rely on would reach their destinations.
Beyond transport, plasma helps regulate body temperature by distributing heat evenly, and it plays a role in maintaining blood pH within a very narrow range. The proteins and electrolytes in plasma act as buffers, neutralizing small amounts of acid or base to keep your blood from becoming too acidic or too alkaline. Plasma also maintains osmotic pressure, the force that keeps the right amount of fluid inside your blood vessels rather than leaking into surrounding tissues.
Plasma vs. Serum
These two terms get confused often, but the difference is straightforward. Plasma is collected by adding an anticoagulant (a substance that prevents clotting) to blood before separating out the cells. Serum is what you get when blood is allowed to clot first. The fibrin clot and clotting factors are then removed by centrifugation, leaving behind a liquid that looks similar to plasma but is missing fibrinogen and several other clotting proteins.
In clinical labs, the choice between plasma and serum depends on what’s being tested. Some blood tests require serum, others require plasma, and the results can differ slightly between the two because of these missing proteins.
Medical Uses of Donated Plasma
Plasma donations are used to create therapies for a surprisingly wide range of conditions. Trauma patients and burn victims receive plasma directly to help with blood clotting and to restore blood volume, which prevents shock. But the majority of donated plasma is processed into specific protein therapies.
These therapies treat people with immune deficiencies, bleeding disorders like hemophilia and von Willebrand disease, certain lung conditions, autoimmune diseases, and neurological conditions like chronic inflammatory polyneuropathy and myasthenia gravis. Plasma-derived antibodies are also used to treat tetanus and rabies infections, and to protect babies during pregnancies complicated by Rh sensitization.
The scale of plasma needed for these treatments is staggering. According to the U.S. Department of Health and Human Services, treating one person with a 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 explain why plasma donation centers are always recruiting.
Plasma as a State of Matter
In physics, plasma refers to something entirely unrelated to blood. It is the fourth state of matter, alongside solids, liquids, and gases. When a gas is heated to extreme temperatures or exposed to a strong electromagnetic field, electrons get stripped away from their atoms. The atoms become positively charged ions, and the freed electrons move independently. This mixture of ions and free electrons is plasma.
Unlike ordinary gas, plasma conducts electricity. The charged particles also interact in complex ways, creating waves and instabilities that make plasma behave very differently from a neutral gas. Lightning, the sun, neon signs, and the aurora borealis are all examples of plasma in action.
Most plasma in the universe exists at extremely high temperatures, often exceeding 10,000 degrees Fahrenheit, with atoms fully stripped of their electrons. But low-temperature plasmas also exist, where atoms are only partially ionized. Some of these can even exist at room temperature. Fluorescent light bulbs, for instance, contain a low-temperature plasma. In fact, plasma is by far the most common state of matter in the visible universe, making up stars, nebulae, and the thin gas between galaxies.