Platelet-rich plasma is not one product. “Leukocyte-poor” and “leukocyte-rich” describe how many white blood cells the preparation keeps. That one variable changes the biology of what is injected.
What it does not seem to change, at least in knee osteoarthritis, is the result. Head to head, the two types have not separated on pain or function. But the rich type has been linked to more soreness and swelling at the site. Here is what the evidence says. And here is why the label alone still does not tell you what you get.
What is the difference between leukocyte-poor and leukocyte-rich PRP?
Both types start with your own blood. The difference is what happens to the white blood cells during processing. Leukocyte-poor types filter most of them out. Leukocyte-rich types keep them in. In the largest randomized comparison, the leukocyte-poor group’s PRP was made with a white-cell filter. The average white cell levels in the two groups ended up about a hundred thousand times apart [2].
What do white blood cells do in PRP?
White blood cells are part of the inflammation phase of healing, and inflammation is not always the enemy. One paper argues that both platelets and white cells help repair. Its reason is that some immune cells (macrophages) can switch from the M1 type to the M2 type. So it says PRP made from the buffy coat layer may help more than it harms [4].
That is an idea about mechanism, not a proven clinical advantage. It is a reason to take the recipe seriously. It is not a reason to assume one type wins.
What the knee osteoarthritis evidence shows
The randomized head-to-head trial
A double-blind randomized trial (Level 1) took 192 patients with painful knee osteoarthritis, Kellgren-Lawrence grade 1 to 3. Each got three weekly shots of PRP. They got either the white-cell-rich type or the white-cell-poor type, assigned at random [2].
The groups did not differ in scores or in how much the scores improved, at any follow-up point. At 12 months, average knee scores (International Knee Documentation Committee, subjective) rose from 45.6 to 60.7 in the leukocyte-rich group. They rose from 46.8 to 62.9 in the leukocyte-poor group (P = .626). Fifteen mild side effects were reported, all knee pain or swelling. They hit 12.2% with leukocyte-rich and 4.7% with leukocyte-poor (P = .101). Failures were 7.8% versus 3.5% (P = .331). The authors concluded that white cells did not significantly change the clinical results [2].
What the pooled reviews add
A review that pooled 32 studies in knee osteoarthritis found both types improved pain and function by more than the smallest change patients notice. There was no significant difference between groups at 3, 6 or 12 months. Local side effects, though, did differ. Pain was significantly more common after leukocyte-rich shots (odds ratio 1.64; 95% CI 1.29 to 2.10; P = .01). So was swelling (odds ratio 1.56; 95% CI 1.22 to 1.99; P = .02) [3].
A 2026 review of 11 studies in living bodies (in vivo) and in the lab (in vitro) reached a similar conclusion. The evidence is not enough to say whether adding white cells helps in osteoarthritis. Results mostly show no significant difference between the two. And there is no solid proof that the local reactions are caused by the white cells themselves [1].
Read together, that is an honest and slightly uncomfortable picture. The recipe changes the biology. It has not yet been shown to change the result you care about.
Why the label is not enough
White cell content is one variable of many. PRP also differs by how long and how hard the blood is spun and how much blood is drawn. It differs by which anti-clot agent is used. The two most common are ethylenediaminetetraacetic acid and citrate, and the research does not agree on which is better. The liquid the platelets end up in differs too. There was no standard way to make it. A proposed standard from 2022 used 40 healthy people. It looked at spin time, spin force and blood volume to fill that gap [1].
That is why two trials can both say they used “leukocyte-rich” platelet-rich plasma and not mean the same product. It is also why the useful question in the room is not which type you are getting. It is what the preparation is designed to do for your tissue.
How formulation fits an evaluation at Regen.MD
At Regen.MD in St. Louis, the recipe is chosen after the diagnosis, not before it. Our evaluation first sets the tissue target and the stage of the problem. Then the preparation is matched to that.
The orthobiologics we offer include joint and tendon PRP in both leukocyte-poor and leukocyte-rich types. They also include PRP placed into the bone (intraosseous and subchondral), bone marrow aspirate concentrate, Lipogems, and intradiscal orthobiologics. For advanced knee osteoarthritis, PRP is discussed as a bridge before joint replacement. No orthobiologic used here is claimed to rebuild lost cartilage. When other care has run out, surgery is part of the path, and Dr. Gurpreet Singh Padda, MD, MBA, MHP is a surgeon.
For more information, get our free guide to knee pain and treatment options.
Get the formulation matched to your diagnosis, not to a label
Regen.MD begins with a physician-led Clinical Evaluation — a review of your history, imaging, and metabolic data, and a written roadmap for what to do next. Evaluation is contingent upon review of your data.
Questions? Call or text us.
Regen.MD, 4477 Woodson Rd, Suite 103, St. Louis, MO 63134, next to St. Louis Lambert International Airport.
What kind of PRP does Regen.MD use?
The recipe questions above are not left open here. Regen.MD makes platelet-rich plasma in two forms. The form is chosen for the tissue being treated. The leukocyte-poor form has no white blood cells and no red blood cells. The leukocyte-rich form keeps the white cells. Both are activated with calcium chloride, at a platelet level of two to three times baseline, with higher dosing in the six to twelve times range.
The target is a measured dose of more than ten billion platelets per joint. Measured, not assumed. Platelet yield varies between patients and between draws. So a protocol stated only as a multiple of baseline can give two people very different total doses on the same day. That is the practice’s own standard, not a finding from any single trial.
Frequently asked questions
Is leukocyte-rich or leukocyte-poor platelet-rich plasma better for knee osteoarthritis?
Head to head, neither has clearly pulled ahead. A Level 1 randomized trial of 192 patients found no difference in scores at any follow-up point. A 2026 review concluded the evidence is not enough to say that adding white cells helps in osteoarthritis. Which type fits your case depends on the tissue being treated. That is part of what we sort out when we evaluate the conditions we treat.
Does leukocyte-rich platelet-rich plasma cause more swelling or pain after the injection?
A review of 32 studies in knee osteoarthritis found pain and swelling at the site were both significantly more common after the rich type than the poor type. A later review said there is no solid proof that the white cells cause those reactions. Our education library covers what to expect after a shot.
Why do two clinics using the same label produce different platelet-rich plasma?
Because the label names one variable, and making PRP involves many. They include spin time, spin force, how much blood is drawn, the anti-clot agent, the liquid used, and whether white cells are filtered out. For years there was no standard way to make it. We walk through how each orthobiologic is prepared before anything is booked.
What should I ask about formulation at my evaluation?
Ask which white-cell type is being used and why. Ask whether the target is inside the joint, inside the bone, or a tendon. And ask how your response and any side effects will be tracked afterward. Those are questions Dr. Gurpreet Singh Padda, MD, MBA, MHP expects and answers directly.
Is PRP leukocyte-rich or leukocyte-poor?
It can be either. Both start with your own blood. The difference is whether processing filters out most of the white blood cells (leukocyte-poor) or keeps them in (leukocyte-rich). The label alone does not tell you everything, because spin time, force, blood volume and anti-clotting agent also vary. Regen.MD makes both. The leukocyte-poor form has no white blood cells and no red blood cells. The leukocyte-rich form is chosen for the tissue being treated.
Can PRP regrow knee cartilage?
No. No orthobiologic used at Regen.MD is claimed to rebuild lost cartilage, whether the PRP is leukocyte-poor or leukocyte-rich. In knee osteoarthritis, both types eased pain and helped function in the studies above, with no significant difference between them. For advanced knee osteoarthritis, PRP is discussed as a bridge before joint replacement. The type is matched to your diagnosis first.
Sources
- Martín-Vega M, Gómez-Carrión Á, Zaragoza-García I, Ortuño-Soriano I, et al. “Leukocyte-rich versus leukocyte-poor platelet-rich plasma for Osteoarthritis: A systematic review.” Regenerative Therapy, 2026. https://pmc.ncbi.nlm.nih.gov/articles/PMC12955565/ — referenced for the 11 analyzed studies, the insufficiency of evidence on added leukocytes, the absence of conclusive evidence linking local reactions to leukocytes, and the preparation variables including centrifugation parameters, anticoagulant choice and resuspension medium.
- Di Martino A, Boffa A, Andriolo L, Romandini I, Altamura SA, Cenacchi A, Roverini V, Zaffagnini S, Filardo G. “Leukocyte-Rich versus Leukocyte-Poor Platelet-Rich Plasma for the Treatment of Knee Osteoarthritis: A Double-Blind Randomized Trial.” American Journal of Sports Medicine, 2022;50(3):609-617. https://pubmed.ncbi.nlm.nih.gov/35103547/ — referenced for the 192-patient population, Kellgren-Lawrence grade 1 to 3 inclusion, three weekly injections, the leukodepletion filter, the International Knee Documentation Committee scores, the adverse-event and failure rates, and the conclusion on leukocytes.
- Kim JH, Park YB, Ha CW, Roh YJ, et al. “Adverse Reactions and Clinical Outcomes for Leukocyte-Poor Versus Leukocyte-Rich Platelet-Rich Plasma in Knee Osteoarthritis: A Systematic Review and Meta-analysis.” Orthopaedic Journal of Sports Medicine, 2021. https://pmc.ncbi.nlm.nih.gov/articles/PMC8255589/ — referenced for the 32 included studies, improvement above the minimal clinically important difference in both groups, the absence of intergroup difference at 3, 6 and 12 months, and the odds ratios for post-injection pain and swelling.
- Lana JF, Huber SC, Purita J, Tambeli CH, Santos GS, Paulus C, Annichino-Bizzacchi JM. “Leukocyte-rich PRP versus leukocyte-poor PRP — The role of monocyte/macrophage function in the healing cascade.” Journal of Clinical Orthopaedics and Trauma, 2019;10(Suppl 1):S7-S12. https://pubmed.ncbi.nlm.nih.gov/31700202/ — referenced for the proposed role of the inflammatory phase, macrophage M1 to M2 plasticity, and the authors’ proposal regarding buffy-coat-derived preparations.