What's in a blood draw: platelet-rich plasma and the cells you already carry

Most of us think of a blood draw as a way to learn something: cholesterol, iron, blood sugar. But the same tube of blood also carries a small supply of repair signals. Concentrating those signals is the idea behind platelet-rich plasma (PRP), the simplest and most widely used form of autologous (from yourself) regenerative therapy.

Your blood is more than red cells

About 55% of blood is plasma, a straw-colored fluid that carries proteins, nutrients, and hormones. The rest is cells. Red blood cells carry oxygen. White blood cells defend against infection. And platelets, tiny cell fragments, are the body's first responders to injury.

When you cut your finger, platelets rush to the site, clump together to stop the bleeding, and release a burst of signaling proteins. Researchers call these growth factors, and they include PDGF, TGF-β, and VEGF. They help recruit other cells, encourage new blood vessel growth, and begin the long work of rebuilding tissue.

How PRP is made

PRP takes that natural process and concentrates it. The steps are straightforward:

1. A small amount of blood is drawn from a vein in the arm, much like a routine lab test.
2. The sample is placed in a centrifuge, which spins it rapidly so its parts separate by weight.
3. Red cells settle to the bottom, and a platelet-rich layer of plasma forms above them.
4. That layer is collected, leaving a concentrate with several times the platelet count of ordinary blood.

The whole process usually takes well under an hour, and nothing is added from outside the body.

PRP doesn't introduce anything new. It gathers what your blood already carries and puts more of it in one place.

Mononuclear cells: the other passengers

Spinning blood also isolates mononuclear cells, a group of white blood cells with a single round nucleus that includes lymphocytes and monocytes. These cells help regulate inflammation and immune signaling. Researchers are studying whether they add to the effects of platelet concentrates.

One point of clarity matters here. Circulating blood contains very few mesenchymal stem cells. PRP works mainly through signals rather than through stem cells. If a source describes a standard blood draw as a stem cell treatment, it's worth asking questions.

What the research says

PRP has been studied for tendon injuries such as tennis elbow, for knee osteoarthritis, and for recovery after some surgeries. Some trials report improvements in pain and function. Others show little difference from comparison treatments. Results depend heavily on how the PRP is prepared, how concentrated it is, and whether white cells are included, and those details vary widely between studies.

The honest summary is that PRP is promising, reasonably well tolerated, and still being refined. It is not a settled answer for every condition.

Why blood is often the starting point

Among the three autologous sources (blood, fat, and bone marrow), blood is the easiest to collect. There's no incision, no anesthetic, and minimal recovery. The trade-off is that blood yields signals and immune cells rather than a rich supply of mesenchymal cells. For those, researchers turn to adipose tissue and bone marrow, which we cover in the next two articles in this series.

Medical Disclaimer: This article is for educational purposes only. Autologous cell therapy, including PRP, is considered investigational for many uses in the U.S., and results in published studies vary. Always consult a qualified healthcare provider before pursuing any treatment.