Does platelet concentration affect how well PRP treats knee osteoarthritis?

Research shows that platelet concentration is associated with clinical improvement in PRP treatment for knee osteoarthritis. In a study of 253 patients, the high-concentration group (more than 1.2 million per mL) had a failure rate of about 3.3%, while the low-concentration group had about 15%, and improvement in the high-concentration group lasted more than 12 months. However, some research suggests that too high a concentration may actually suppress the cellular response, forming a bell-shaped dose-response curve.

Does PRP have to be leukocyte-rich?

A recent randomized double-blind controlled trial divided 132 patients with knee osteoarthritis into a leukocyte-rich (LR-PRP) group and a leukocyte-poor (LP-PRP) group. After one year of follow-up, there was no significant difference in pain improvement, functional activity, or satisfaction, and the safety of the two was comparable. In clinical practice, the choice can be made flexibly based on the individual patient's situation.

What aspects of PRP treatment for knee osteoarthritis still need clarification?

PRP preparation methods and platelet concentration are not yet fully standardized. In the future, establishing a unified platelet concentration standard, standardizing treatment protocols, and defining clear indications may help improve the objectivity and reproducibility of outcomes. It is best to discuss your individual situation with a physician before treatment.

Key Factors in PRP Injections for Knee Osteoarthritis: Platelet Concentration and White Blood Cells

As the population ages and more people stay physically active, patients with knee osteoarthritis (OA) are becoming more common, and demand for effective, longer-lasting non-surgical treatment is gradually increasing. Among these options, platelet-rich plasma (PRP) injection for knee osteoarthritis has drawn a great deal of attention in recent years. The effect and safety of PRP may be influenced by platelet concentration and white blood cell (leukocyte) content, making these important and worthwhile key factors to explore in clinical use.

The challenges of knee osteoarthritis

Typical features of knee osteoarthritis include degeneration of the joint cartilage, pain, inflammation, and limited movement. Existing treatments such as oral painkillers, corticosteroid injections, and hyaluronic acid injections can relieve symptoms in the short term, but they cannot effectively change the course of the disease or achieve long-lasting effects. Finding treatments with greater repair potential has therefore become an important clinical goal.

How PRP works

Platelet-rich plasma (PRP) is a high-concentration platelet plasma extracted from the patient’s own blood. It is rich in various growth factors and cytokines that can promote cellular repair, modulate the inflammatory response, and may relieve pain, improve function, and even slow disease progression. However, the effect of PRP is not uniform. Research shows that its effect is clearly related to the PRP preparation method, platelet concentration, and white blood cell content.

Defining platelet concentration

Platelet concentration in PRP is usually described as a multiple, that is, the multiple of platelet concentration relative to the patient’s whole venous blood: low-concentration PRP is about 1.5 to 2 times; medium concentration is 2 to 4 times; and high concentration is more than 4 times. Some studies suggest that 5 to 6 times or more may achieve better results, while other research shows that if platelet concentration exceeds a certain threshold (such as more than 8 to 10 times), the high concentration of growth factors released may suppress the cellular response or increase the inflammatory reaction, forming a bell-shaped dose-response curve. In other words, a concentration that is too high or too low may reduce the effect.

Platelet concentration refers to the number of platelets contained in each mL of PRP, generally expressed as platelets per mL (platelets/mL). According to recent research, the higher the platelet concentration of PRP, the more significant the clinical improvement it provides in treating patients with knee osteoarthritis, especially in pain relief and functional recovery.

In the study, 253 patients were divided into three groups by platelet concentration: high (more than 1,200,000 platelets/mL), medium (800,000 to 1,200,000 platelets/mL), and low (below 800,000 platelets/mL). The results showed that the high-concentration platelet group had the lowest failure rate (about 3.3%), while the low-concentration group had the highest failure rate (up to 15%), and improvement in the high-concentration group lasted more than 12 months. Based on this study, clinicians may consider prioritizing PRP with a higher platelet concentration, which was associated with better outcomes and a lower failure rate in this cohort.

Defining white blood cell classification

Based on their concentration, the white blood cell content in PRP can be divided into leukocyte-rich PRP (LR-PRP) and leukocyte-poor PRP (LP-PRP). Early research suggested that white blood cells might promote inflammation within the joint and have a negative effect on outcomes; however, other research argued that white blood cells can secrete a variety of active substances that help control the inflammatory response within the joint.

A recent randomized double-blind controlled trial in AJSM indicated that the level of white blood cell concentration did not significantly affect the efficacy and safety of PRP treatment for knee osteoarthritis. This study randomly assigned 132 patients with knee osteoarthritis to receive either leukocyte-rich PRP (LR-PRP) or leukocyte-poor PRP (LP-PRP) injections. After one year of follow-up, the two groups showed no significant difference in pain improvement, functional activity, or patient satisfaction, and the safety of the two types of PRP was comparable.

This suggests that white blood cell concentration may not be an important factor influencing the effect of PRP treatment for knee osteoarthritis, and that in clinical practice, PRP with different white blood cell concentrations can be chosen flexibly according to the individual patient’s situation.

Summary

PRP is one of the non-surgical options studied for knee osteoarthritis, and appears relatively safe in the populations studied. Taking the above research together, one clinical direction is to prioritize PRP with a higher platelet concentration, which was associated with better outcomes and a lower failure rate in the cited study; as for white blood cell concentration, there is no strong clinical recommendation, and it can be adjusted flexibly according to patient characteristics or response.

In the future, PRP treatment should be more standardized, for example by establishing a unified standard for platelet concentration, standardizing the treatment protocol, and defining clear patient indications, so as to further improve treatment effectiveness and provide more objective and reproducible outcomes.

References

Influence of Platelet Concentration on the Clinical Outcome of Platelet-Rich Plasma Injections in Knee Osteoarthritis. The American Journal of Sports Medicine, 52(13), 3223–3231.
Leukocytes Do Not Influence the Safety and Efficacy of Platelet-Rich Plasma Injections for the Treatment of Knee Osteoarthritis: A Double-Blind Randomized Controlled Trial. The American Journal of Sports Medicine, 52(13), 3212–3222
Platelet-Rich Plasma for Knee Osteoarthritis: A Comprehensive Narrative Review of the Mechanisms, Preparation Protocols, and Clinical Evidence. Journal of Clinical Medicine, 14, 3983.