What is PRP, a treatment prepared from your blood?

What is PRP made from?

Plasma is the pale liquid part of your blood, and it carries blood cells around your body. A spinning machine separates the layers and keeps platelets in some of that plasma. Platelets are tiny pieces in blood that gather where tissue is hurt. The finished liquid comes only from your own blood, not from another person.

Machines don’t all keep the same mix of blood parts after spinning. Some machines keep many white cells; others leave only a few. The clinic can tell you which kind it plans to use for your sore area.

How many PRP injections are needed?

There isn’t one schedule for every person or every sore area. Some care plans involve one treatment, while others include later treatments. Your exam, the joint involved, and your response help guide that choice. Ask when your progress will be checked and what could end the plan early.

Is leukocyte rich PRP the kind with more white blood cells?

Yes. The kind named in the heading keeps more white blood cells, and the other kind leaves few. The form with more white cells is linked with more soreness afterward. The form with most white cells removed is often gentler, though either kind can cause a short period of aching or swelling.

Sources

1. The PAW classification was proposed because PRP preparation protocols 'vary widely between authors and are often not well documented in the literature, making results difficult to compare or replicate'. It sorts preparations by three variables: the absolute number of Platelets, the manner of Activation, and the presence or absence of White cells - the three levers that make two injections both called 'PRP' materially different products.

   DeLong JM, Russell RP, Mazzocca AD — Platelet-rich plasma: the PAW classification system. Arthroscopy, 2012. DOI: 10.1016/j.arthro.2012.04.148.

2. The DEPA classification was built because platelet and leukocyte counts alone do not describe an injection. Applied retrospectively to 20 published PRP preparations, the dose of injected platelets ranged from 0.21 billion to 5.43 billion - a 25-fold spread. No device recovered more than 90% of the platelets in the blood drawn, and most preparations were contaminated with red blood cells: only three of the devices reached a purity score corresponding to more than 90% platelets relative to red cells and leukocytes.

   Magalon J, Chateau AL, Bertrand B, et al. — DEPA classification: a proposal for standardising PRP use and a retrospective application of available devices. BMJ Open Sport & Exercise Medicine, 2016. DOI: 10.1136/bmjsem-2015-000060.

3. A systematic review that screened 876 studies and extracted standardised data from 33 commercially available PRP systems and protocols found that final product concentrations of platelets, white cells and growth factors varied widely between systems, as did the preparation protocols themselves. Platelet concentration correlated directly with the volume of blood drawn and with the centrifugal force of the device. The authors called the heterogeneity between separation systems something that 'must be resolved for proper study of this promising treatment'.

   Fadadu PP, Mazzola AJ, Hunter CW, et al. — Review of concentration yields in commercially available platelet-rich plasma (PRP) systems: a call for PRP standardization. Regional Anesthesia and Pain Medicine, 2019. DOI: 10.1136/rapm-2018-100356.

4. A narrative review of PRP concluded that the literature suggests leukocyte-rich PRP is more beneficial in tendinopathies while pure (leukocyte-poor) PRP is more beneficial in cartilage pathology - but stated plainly that different PRP preparations have not been directly compared head-to-head in ANY pathology, and that the PRP type used is frequently not even stated in published research.

   Collins T, Alexander D, Barkatali B — Platelet-rich plasma: a narrative review. EFORT Open Reviews, 2021. DOI: 10.1302/2058-5241.6.200017.

5. A Bayesian network meta-analysis of nine studies (six RCTs, 1055 patients) found leukocyte-POOR PRP produced significantly better WOMAC scores than hyaluronic acid (mean difference -21.14; 95% CI -39.63 to -2.65) and than placebo (-17.84; 95% CI -34.95 to -0.73), while leukocyte-RICH PRP showed no such significant difference versus placebo. PRP of either type caused more local adverse reactions than hyaluronic acid (OR 5.63; 95% CI 1.38-22.90), almost always local swelling and pain, with no difference in safety between the two PRP types.

   Riboh JC, Saltzman BM, Yanke AB, et al. — Effect of Leukocyte Concentration on the Efficacy of Platelet-Rich Plasma in the Treatment of Knee Osteoarthritis. American Journal of Sports Medicine, 2016. DOI: 10.1177/0363546515580787.

6. A systematic review of 29 randomized trials of PRP for knee OA that reported a platelet count, concentration or dose found that the 28 treatment arms with statistically significant positive outcomes at 6 months had a mean platelet dose of 5,500 (+/-474) x 10^6, while the three arms without a positive difference averaged 2,302 (+/-437) x 10^6 (P<.01). The same separation held at 12 months: 5,464 versus 2,253 x 10^6 (P<.05).

   Berrigan WA, Bailowitz Z, Park A, et al. — A Greater Platelet Dose May Yield Better Clinical Outcomes for Platelet-Rich Plasma in the Treatment of Knee Osteoarthritis: A Systematic Review. Arthroscopy, 2025. DOI: 10.1016/j.arthro.2024.03.018.

7. A triple-blind randomized trial in 99 knees with early (KL 1-2) knee OA compared a conventional 4 mL PRP dose (mean 2.82 billion platelets) with an 8 mL 'superdose' (mean 5.65 billion), both leukocyte-depleted and prepared identically. Both groups improved on WOMAC, VAS and KOOS over six months. The trial is a direct demonstration that 'a PRP injection' is not one intervention: the same preparation at two volumes delivers a two-fold difference in platelet dose.

   Patel S, Gahlaut S, Thami T, et al. — Comparison of Conventional Dose Versus Superdose Platelet-Rich Plasma for Knee Osteoarthritis: A Prospective, Triple-Blind, Randomized Clinical Trial. Orthopaedic Journal of Sports Medicine, 2024. DOI: 10.1177/23259671241227863.

8. A systematic review and meta-analysis of adverse events in randomized trials of intra-articular PRP for knee osteoarthritis found PRP associated with mild, transient adverse events - knee pain and swelling - that typically resolve without intervention, and more frequent with LEUKOCYTE-RICH formulations. Leukocyte-poor PRP had a safety profile similar to hyaluronic acid. Knee stiffness was more frequent with PRP than with normal saline (P=.031). No severe adverse events were reported in any group.

   Nakagawa HF, Kim J, Rabinowitz J, et al. — Assessment of adverse events and safety associated with intra-articular platelet-rich plasma injections compared to other injectates for knee osteoarthritis: A systematic review and meta-analysis. PM&R, 2026. DOI: 10.1002/pmrj.70141.

9. A systematic review of 105 clinical PRP studies in orthopaedics published 2006-2016 found that only 11 (10%) described the preparation protocol clearly enough for another investigator to repeat it, and only 17 (16%) reported any quantitative metric of the final PRP composition. The authors concluded that the current reporting of PRP preparation and composition does not allow the PRP products actually delivered to patients to be compared between studies.

   Chahla J, Cinque ME, Piuzzi NS, et al. — A Call for Standardization in Platelet-Rich Plasma Preparation Protocols and Composition Reporting: A Systematic Review of the Clinical Orthopaedic Literature. Journal of Bone and Joint Surgery (American), 2017. DOI: 10.2106/JBJS.16.01374.