The field knew about this problem in 2017 and wrote a standard for it

In 2017 Murray and colleagues published the Minimum Information for Studies Evaluating Biologics in Orthopaedics — MIBO — a formal Delphi consensus producing a 23-statement checklist of what a clinical study of PRP must report. Twenty-three experts, three survey rounds, published in the Journal of Bone and Joint Surgery.

Does the platelet dose in PRP affect results?

Once studies started counting, a relationship appeared.

• Bansal and colleagues (2021), in Scientific Reports, concluded that an absolute count of roughly 10 billion platelets is critical to a sustained effect at one year in moderate knee osteoarthritis, with WOMAC and IKDC advantages over hyaluronic acid persisting to twelve months and measurable declines in IL-6 and TNF-α.
• Berrigan and colleagues (2024) pooled the dose literature and reported a dose–response relationship for knee osteoarthritis, identifying a threshold above 10 billion platelets for favorable outcomes, with the effect more pronounced for function than for pain.
• Hooper and colleagues (2026), in PM&R, found outcomes associated with total deliverable platelets, with 5 to 10 billion associated with greater functional improvement.
• Patel and colleagues (2024) ran a prospective, triple-blind randomized trial comparing a conventional dose against a superdose containing roughly twice the platelets. The higher dose produced significantly better pain and function, and 96% versus 68% satisfaction at six months.

Berrigan and Hooper do not agree on the exact optimum, and that disagreement is worth stating rather than smoothing over. What they agree on is the part that matters here: dose is a variable that changes the result. A study that did not measure it cannot be pooled with one that did and produce a meaningful average.

Does PRP composition matter, not only the platelet count?

Kim and colleagues (2021) separated leukocyte-poor from leukocyte-rich preparations across the knee osteoarthritis literature. Intra-articular PRP improved pain and function above the minimal clinically important difference out to twelve months, and the risk of local adverse reactions was higher after leukocyte-rich than leukocyte-poor preparation.

So two injections both labeled “PRP” can differ in the concentrate delivered, in whether white cells were included, in whether the platelets were activated, and in the volume injected. Treating them as one intervention is a methodological error, not a conservative choice.

Patel’s superdose arm also had more short, self-limiting soreness in the days after injection. More is not free, and the practice does not pretend otherwise.

What does a negative PRP study actually show?

The authors generally say so themselves. Pei and colleagues (2026), reviewing PRP for low back pain, report reduced pain and disability to six months and then explicitly caution that their findings must be interpreted carefully because of substantial heterogeneity across studies. Heterogeneity is the recurring stated limitation in this literature, and preparation is a large part of what is heterogeneous.

This is not a way of dismissing unfavorable evidence. It is the reason the practice quotes the trials that characterized their product and does not lean on the ones that did not — in either direction.

What we can say about what we inject

The clinically relevant consequence is simple: a preparation should be specified, and the specification should be in the record. Where a client received PRP elsewhere and the composition was never documented, that is a genuine gap in the file and we will say so rather than assume a dose.

This practice is not aligned to a side. Its obligation runs to the patient’s health and safety, which is the same reason it is not beholden to any position that would keep it from seeing what is actually there. We do not offer opinions on liability, we do not accept a referral or a review conditioned on reaching a particular conclusion, and we will say plainly when the evidence does not support the claim — whichever party was hoping otherwise.

Frequently asked questions

Does this mean older negative PRP studies were wrong?

Not wrong — narrower than they are usually quoted. A trial of an uncharacterized preparation is evidence about that preparation. It is not evidence about a dose-specified product, because the trial never established which one it used.

Is there an agreed optimal platelet dose?

Not yet. Berrigan reports a threshold above 10 billion for knee osteoarthritis; Hooper found 5 to 10 billion associated with greater functional gain. The field agrees dose matters and has not settled the number.

Why does leukocyte content matter?

Kim and colleagues found leukocyte-rich preparations carried a higher risk of local adverse reactions than leukocyte-poor ones in the knee, with both improving pain and function above the clinically important threshold.

How should an attorney use this?

To ask a reviewing expert relying on a null meta-analysis which platelet doses were pooled, and whether the constituent trials met MIBO reporting. See expert testimony.

Is all PRP the same?

No. “PRP” names a category, not a product. Two injections both labeled PRP can differ in platelet concentration and dose, in whether white cells were included, in whether the platelets were activated, and in the volume injected. Concentration, platelet dose, leukocyte content and activation all vary by an order of magnitude between preparations. Treating them as one intervention is a methodological error, which is why the preparation belongs in the record.

Why does PRP work in some studies and not others?

Largely because of what was injected. Studies that report platelet dose find a dose–response relationship, and much of the older literature never stated what was in the syringe. A meta-analysis that pools uncharacterized preparations shows only that the mixture, averaged together, did not separate from a comparator. It has not shown that a dose-specified preparation fails.

Does a higher PRP dose cause more side effects?

Somewhat. In Patel’s 2024 triple-blind randomized trial, the superdose arm, with roughly twice the platelets, produced significantly better pain and function but also more short, self-limiting soreness in the days after the injection. More is not free, and this practice does not pretend otherwise.

Related reading

• What the evidence actually says
• Orthobiologics: PRP and BMAC
• A denial is a budgeting decision
• Expert testimony
• Future care and damages