By: Dr Zaid Matti
Musculoskeletal Medicine Specialist
In recent years, platelet-rich plasma (PRP) therapy has emerged as a compelling non-surgical treatment option for knee osteoarthritis (OA), particularly in its early to moderate stages. With hundreds of clinics and providers offering PRP injections, it’s easy to assume that all PRP treatments are equal. But they’re not—and one of the most critical, yet overlooked, factors is the total platelet dose delivered.
A new meta-analysis published in The American Journal of Sports Medicine (Bensa et al., 2025) sheds important light on this issue. By pooling results from 18 high-level placebo-controlled trials, the authors not only confirmed that PRP is clinically effective for knee OA—but they also identified platelet concentration as a key driver of that efficacy.
What the Study Showed
The review included 1,995 patients and analyzed outcomes using standardized pain and function scales (VAS and WOMAC) at 1, 3, 6, and 12 months after treatment. PRP injections consistently outperformed placebo—not only statistically, but also in a way that patients could feel, reaching what is known as the Minimal Clinically Important Difference (MCID).
But here’s the real kicker:
Only high-platelet concentration PRP consistently achieved lasting pain relief and functional improvements at 3, 6, and 12 months.
Low-platelet PRP (often what’s produced by basic or budget systems) might show short-term benefits, but these often fade by the 6–12 month mark. In contrast, PRP with higher platelet concentration sustained its effect over time.
Why Concentration Alone Is Not Enough
Concentration tells you how densely packed the platelets are—but it doesn’t tell you how many platelets you’re actually getting. That’s where total dose comes in.
Let’s break it down:
- Whole blood contains about 200 billion platelets per 10 mL of blood.
- If a device concentrates this to 5 mL of PRP, you would theoretically get a maximum of 200 billion platelets total—but in reality, most commercial systems recover far less.
- Many automated PRP systems recover only 10%–30% of available platelets, meaning you may receive just 2 to 6 billion platelets per injection—far below the optimal therapeutic threshold in some cases.
According to expert consensus and laboratory data, a minimum effective PRP dose is 5–10 billion platelets, with the higher end recommended for:
- Older adults
- Patients with more severe osteoarthritis
- People with slower healing capacity
Anything below that is unlikely to achieve durable results, which may explain why some patients don’t respond even after multiple injections.
More Is Not Always Enough—Quality and Quantity Matter
To compensate for low platelet yield, some protocols suggest multiple injections (e.g., 3 doses). But as the Bensa et al. study suggests, quality trumps quantity. High-dose, high-concentration PRP not only produced greater improvements—it also sustained those improvements longer, making a strong case for optimizing the platelet dose per injection rather than simply repeating subtherapeutic treatments.
So What Does That Mean for Patients?
If you’ve been recommended PRP, it’s essential to ask:
- How much blood is being taken?
- What’s the final volume of PRP injected?
- How concentrated is it?
- And—most importantly—how many total platelets are being delivered?
For example, if your doctor draws 10 mL of blood, that contains about 200 billion platelets. No system can magically create more than that—it can only concentrate what’s available. If the device recovers only a fraction of that, your final PRP dose may fall well below the levels shown to be effective in clinical trials.
Bottom Line
The latest evidence confirms:
It’s not just about injecting PRP—it’s about injecting the right dose.
If you’re considering PRP therapy, understanding the total platelet dose you’re receiving can help set realistic expectations and ensure you’re getting a scientifically supported treatment—not just a biologic buzzword.
Reference
Bensa A, Previtali D, Sangiorgio A, et al. PRP Injections for the Treatment of Knee Osteoarthritis: The Improvement Is Clinically Significant and Influenced by Platelet Concentration. Am J Sports Med. 2025;53(3):745–754. doi:10.1177/03635465241246524