plasma
Meaning of plasma: Plasma and serum are not interchangeable, since serum is what remains after blood clots and has given up its clotting proteins in the process.
Definition of plasma
Plasma is the liquid part of blood, a straw-colored fluid making up a little over half its volume and holding the blood cells in suspension. It is mostly water, carrying dissolved proteins, salts, sugars, hormones, gases, nutrients and waste. Its proteins include albumin, the clotting factors and antibodies, so plasma does considerably more than transport.
What do the plasma proteins do?
Albumin is the most abundant. It binds and carries hormones, drugs and waste products that will not dissolve in water on their own, and it exerts the pull that holds fluid inside vessels. When albumin falls, as in liver disease or severe malnutrition, that pull weakens and fluid seeps into tissue, producing swelling. Clotting factors circulate inactive until injury triggers a cascade that converts fibrinogen into a fibrin mesh. Antibodies, made by plasma cells, circulate here too, which is why the fluid rather than the cells carries much of the body's immune function.
How does it differ from serum and whole blood?
| Sample | What it contains |
|---|---|
| Whole blood | Cells plus plasma, as drawn |
| Plasma | The fluid separated with an anticoagulant, so clotting proteins remain |
| Serum | The fluid left after blood has clotted; clotting factors are consumed |
| Packed red cells | The cellular portion with most of the fluid removed |
Laboratories specify which is required, because a test measuring a clotting factor is meaningless in serum, and some measurements differ between the two.
How is donated plasma used?
It can be given directly, as fresh frozen plasma, to replace clotting factors when many are missing at once, such as in severe bleeding or liver failure. More often it is fractionated, meaning individual proteins are separated out on an industrial scale: albumin solutions, immunoglobulin preparations for people who cannot make antibodies, and concentrated clotting factors for hemophilia. Because these products are pooled from many donors, screening and viral inactivation steps are built into manufacture. A related procedure, plasma exchange, removes a person's own plasma and replaces it, in order to strip out harmful antibodies rather than to correct a shortage, and it is distinct from blood transfusion in purpose.
Used in a sentence
The laboratory separated plasma from the blood sample for further protein analysis.
Good to know
Plasma is distinct from serum, the fluid that remains after blood has been allowed to clot, since serum lacks the clotting proteins that plasma still contains.
Word origin
Where “plasma” comes from
From Greek plasma, meaning something formed or molded, later adopted to describe the fluid portion of blood.