Squeeze a story about blood donation into one image and it’s always red. But more than half of your blood isn’t red at all, it’s a pale straw-coloured liquid called plasma, and without it the red stuff would be a useless sediment at the bottom of a tube.
What plasma is
Plasma is the liquid portion of blood, roughly 55% of its volume. Its composition is beautifully simple and astonishingly busy at the same time:
- About 90% water, the universal solvent that keeps everything flowing.
- 7–8% proteins, the heavy hitters described below.
- The remainder, salts (electrolytes), glucose, fats, hormones, vitamins, and waste products on their way to the kidneys or liver.
Suspended in this liquid are your red cells, white cells and platelets. Plasma is the river; they’re the traffic.
The three great protein families
Plasma’s proteins do the heavy lifting:
- Albumin, the most abundant plasma protein. It acts like a sponge, holding fluid inside your blood vessels so they don’t leak it into tissues. It also shuttles hormones and drugs around the body.
- Clotting factors, a dozen-odd proteins that circulate quietly until injury activates them in a chain reaction (the cascade described in our platelet article), producing the fibrin mesh that seals wounds.
- Antibodies (immunoglobulins), the immune system’s guided missiles, made by B lymphocytes, tagging pathogens for destruction. Plasma from recovered patients even carries antibodies against diseases they’ve beaten, the basis of some therapies.
What plasma actually does
Beyond carrying its protein cargo, plasma performs the unglamorous logistics that keep you alive: distributing nutrients from your gut, collecting wastes for disposal, ferrying hormones between glands and targets, and buffering your body’s acid–base balance so your blood’s pH stays within a whisker of where it must be.
Why freezing matters
Different blood components have wildly different shelf lives. Red cells keep for weeks refrigerated. Platelets last about five days at room temperature. Plasma, by contrast, can be frozen quickly after donation and stored for up to a year at very low temperatures. Freezing preserves the clotting factors that are plasma’s main clinical value, which is why frozen plasma is a standard hospital stock item, ready for emergencies years after the donation that supplied it.
Who needs donated plasma
Plasma transfusions save lives in a specific set of situations:
- Massive bleeding and trauma, when a patient loses large volumes, replacing red cells alone isn’t enough; they need clotting factors too, or the bleeding won’t stop.
- Severe burns, burned skin leaks plasma at an enormous rate; restoring fluid and protein volume is critical.
- Liver disease, the liver makes most clotting factors, so a failing liver leaves patients deficient; plasma can temporarily supply what the liver can’t.
- Clotting disorders, when specific factors are missing or overwhelmed (such as in disseminated intravascular coagulation), donated plasma is a ready-made replacement.
The universal donor, in liquid form
Here’s a elegant twist: type AB plasma is special. While AB red cells can only go to AB patients, AB plasma contains neither anti-A nor anti-B antibodies, so it can be given to patients of any blood group. In an emergency where there’s no time to crossmatch, AB plasma is the universal stopgap. Our article on the AB positive blood group explains why this works.
Donate, carry everything to everyone
When you donate whole blood, your plasma is separated, frozen, and banked for up to a year of readiness. One donation quietly stocks the emergency shelf for burns, liver crises, and trauma cases.
Register as a blood donor, it takes minutes. Want to understand the full picture of what your donation becomes? Start with what blood actually is, or see how often you can donate.