Clinics advertise platelet concentration the way engines are advertised by horsepower — higher implying better. The published evidence does not support that, and in one tissue type it points the other way.
This matters commercially as well as clinically, because concentration is frequently what a premium price is justified by.
The number that matters: 750,000 per microlitre
Robert Stall, MD teaches the finding directly. Platelet concentrations from above baseline up to roughly 750,000 platelets per microlitre — about one to four times whole blood — are supported as effective for tissue regeneration by several clinical trials.
Above that line, the benefit does not continue: “there was no evidence that platelet concentrations greater than 750,000 necessarily provided any better tissue regeneration in soft tissue injury.”
Not “less benefit”. No evidence of additional benefit at all.
Where higher was actively worse
The stronger finding concerns bone. At very high concentrations the effect on bone regeneration was inhibitory, and Stall's description of the outcome is unambiguous: those subjects “did worse than controls who had no PRP treatment at all.”
Worse than nothing. That is a dose-response curve that turns downward, not one that plateaus — and it is the clearest possible argument against treating concentration as a quality metric.
Why that is biologically unsurprising
PRP does not work by flooding tissue with platelets. It works by delivering the growth factors released from platelet alpha granules, which initiate a signalling cascade the tissue then responds to.
Signalling systems have optimal ranges. Overwhelming a receptor population does not produce proportionally more response, and in several biological systems produces less. Tumour necrosis factor alpha, one of the cytokines involved, is an inflammatory mediator that can drive necrosis or apoptosis — more inflammatory signal is not automatically more healing.
Expecting a linear relationship between platelet count and tissue repair assumes a mechanism PRP does not have.
Why you cannot compare two clinics on concentration alone
Concentration is one of three variables, and the field has never agreed on how to report any of them. Stall is blunt: multiple classification systems exist and “none of these classification systems have been universally accepted as a universal standard, giving rise in part to the confusion.”
The PAW system captures the three that matter — Platelets, Activation, White cells:
- Platelet concentration, in four bands: at or below baseline; baseline to 750,000; 750,000 to 1,250,000; above 1,250,000 per microlitre.
- Activation — whether an exogenous activator such as calcium chloride was used.
- White cells — present or absent.
A parallel system classifies by leukocyte content and fibrin architecture: P-PRP, L-PRP, P-PRF and L-PRF. Stall notes that pure platelet-rich fibrin, with no white cells and a high fibrin matrix, is the formulation favoured for orthopaedic indications and particularly for knee osteoarthritis.
So two preparations both called “PRP” may differ in platelet concentration fourfold, contain opposite leukocyte content, and be activated differently. Comparing them on a single advertised number compares almost nothing.
What this does to the published literature
It explains the contradictions better than any argument about study quality.
Trials using preparations inside the effective range report benefit. Trials using very concentrated preparations may report none. Both are published as “PRP”. Pool them in a meta-analysis and the result is an average that describes neither group.
This is worth understanding before dismissing the category on the strength of a negative review, and equally before accepting a positive one. The question is always which preparation.
What to ask a clinic
- What platelet concentration does your system produce, as a multiple of my baseline? A clinic that has never measured its own output cannot answer this.
- Leukocyte-rich or leukocyte-poor, and why that choice for my condition?
- Is an exogenous activator used?
- Is the target concentration different for tendon than for a joint? If the answer is no, ask why.
- Why should I pay more for a higher concentration, given the evidence above 750,000?
A clinic that engages with these is characterising its preparation. One that answers only “we use the best system available” is answering a marketing question with a marketing answer.
For clinicians choosing a system
The commercial pressure runs toward advertising the highest achievable concentration, and the evidence does not reward it. A system producing a characterised, reproducible preparation in the supported range, with known leukocyte content, is defensible. One selected for a headline concentration figure above 750,000 is selected on a claim the literature does not carry — and in bone, contradicts.
The wider picture, including the healing phases and the regulatory frame, is in the regenerative pain medicine reference.
Learn blocks with your hands, not from a page
Empire’s Pain Management Training (THE Pain Show) is accredited for 25.25 AMA PRA Category 1 Credits™, jointly provided by AKH, Inc, and Empire Medical Training. For narrower peripheral work, Joint, Extremity and Non-Spinal Injection Training carries 6.75 credits for the complete in-person hybrid program, and Advanced Musculoskeletal Ultrasound Guided Injections builds the guidance skills above.
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