Platelet rich plasma (PRP) injections use a concentrated sample of your own platelets, taken from a routine blood draw and spun in a centrifuge, to deliver growth factors directly into an injured tendon, joint, or area of skin. The idea is to support the body’s natural repair process. PRP has been described as a revolutionary approach in regenerative medicine, and it is widely used for knee osteoarthritis, tendon problems, and hair loss, but the evidence varies considerably between conditions.
From a hematology point of view, PRP is interesting because it repurposes something platelets already do every day. Below, I explain how PRP works, how it is prepared, which conditions it is used for, who should avoid it, and what a realistic outcome looks like.
What Is Platelet Rich Plasma?
Plasma is the yellowish liquid part of blood. Platelets, also called thrombocytes, are small cell fragments that circulate in it. Their best-known job is to plug damaged blood vessels and start clotting, but they also carry granules packed with signaling proteins that help tissues heal.
Platelet rich plasma is plasma with a platelet concentration several times higher than normal blood. A normal platelet count is roughly 150 to 450 × 10⁹ per liter. PRP concentrates those platelets into a small volume so that more healing signals can be delivered to one spot.
Because PRP comes from your own blood, it is called autologous. That means there is no risk of an allergic or immune reaction to donor material and no risk of catching an infection from another person’s blood.
How PRP Works: Growth Factors and Platelet Activation
When platelets are activated, they release proteins stored in their granules. The best known is platelet-derived growth factor (PDGF), which attracts repair cells and stimulates them to divide. Our article on PDGF’s role in vascular biology and disease goes deeper into its effects on blood vessels.
Other important signals include transforming growth factor-beta (TGF-beta), which influences collagen production and scar formation, and vascular endothelial growth factor (VEGF), which promotes new small blood vessels. Together they help regulate inflammation, cell growth, and tissue remodeling.
How and when platelets release these signals depends on platelet activation. Some PRP systems add an activating agent before injection; others rely on contact with the injured tissue to trigger release.
How PRP Is Prepared and Injected
A PRP treatment is usually done in a single outpatient visit and follows a predictable sequence.
- Blood draw: a small amount of blood is taken from the arm, similar to a routine blood test.
- Centrifugation: the tube is spun at high speed, which separates red cells, a thin platelet and white cell layer, and plasma.
- Concentration: the platelet-rich layer is drawn off. Depending on the system, it may be leukocyte-rich (containing more white cells) or leukocyte-poor.
- Injection: the PRP is injected into the target area, often with ultrasound guidance for tendons and joints.
Preparation methods are not standardized, so the platelet concentration and white cell content vary between clinics and devices. This variability is one reason research results differ.
What PRP Is Used For
PRP is used across orthopedics, sports medicine, dermatology, and dentistry. The strength of evidence is not the same for each use.
| Condition | How PRP is used | State of the evidence |
|---|---|---|
| Knee osteoarthritis | Injection into the joint | Among the most studied uses; may reduce pain for some patients |
| Tennis elbow and other tendinopathies | Injection into the damaged tendon | Widely used; results vary between tendons and studies |
| Androgenetic hair loss | Series of scalp injections | Used increasingly; response is variable |
| Chronic wounds | Applied topically or as a gel | Used in selected wound-care settings |
| Acute muscle injuries | Injection into the injured muscle | Evidence of benefit is limited |
PRP is usually combined with physiotherapy, activity modification, and strengthening. It works best as part of a rehabilitation plan rather than as a standalone fix.
Who Should Avoid PRP
PRP depends on healthy, functioning platelets, so blood conditions matter. Contraindications usually include:
- a low platelet count (thrombocytopenia) or a known platelet function disorder
- other hematologic disorders that affect clotting or blood counts
- active infection at or near the injection site, or a systemic infection
- active cancer, particularly blood cancers or cancer near the treatment area
- significant anemia or being generally unwell on the day
If you take blood thinners or anti-inflammatory medicines, tell the clinician beforehand. Anti-inflammatory drugs can blunt platelet function, and clinics often ask patients to pause them for a period before and after treatment where it is safe to do so. For more on how platelets work and what can go wrong with them, see our platelets guide.
Side Effects, Recovery, and Cost
Because PRP is autologous, serious side effects are uncommon. The most frequent are pain, swelling, and stiffness at the injection site for a few days, along with bruising where blood was drawn. Infection is rare when sterile technique is used.
Improvement, if it comes, is gradual. Growth factors support repair over weeks, so patients are usually reassessed after several weeks to a few months, and some protocols involve a series of injections. PRP is often not covered by insurance. Our article on the cost and value of platelet rich plasma injection covers pricing and how to weigh it.
Questions to ask before booking
- What diagnosis is the PRP treating, and has it been confirmed by examination or imaging?
- Which preparation system is used, and is the PRP leukocyte-rich or leukocyte-poor?
- Will the injection be guided by ultrasound?
- How many injections are planned, and what is the total cost?
- What rehabilitation or physiotherapy should go alongside it?
- How will we judge whether it has worked, and when?
A clinician who answers these clearly, and who is honest about the limits of the evidence for your condition, is a good sign.
Frequently Asked Questions
Are platelet rich plasma injections painful?
The blood draw feels like a routine blood test. The injection itself can be uncomfortable, especially into a tendon, and many clinics use local anesthetic. Soreness for a few days afterwards is common and usually settles on its own.
How many PRP injections will I need?
It depends on the condition and the protocol. Some tendon problems are treated with a single injection, while knee arthritis and hair loss protocols often involve a series spaced weeks apart. Your clinician should explain the plan before you start.
Is PRP safe if I have a blood disorder?
Not always. Low platelet counts, platelet function disorders, and some blood cancers are standard contraindications. If you have any blood condition, discuss PRP with your hematologist before booking.
Is PRP really a revolutionary approach in regenerative medicine?
It is a genuinely useful idea that harnesses the body’s own healing signals, and it helps some patients. However, results vary by condition and by how the PRP is prepared. It is best seen as one option within a broader treatment plan, not a guaranteed cure.
