Platelet-rich plasma (PRP) is a product that contains a high concentration of platelets from the person’s own blood serum (the clear part of the blood). The normal amount of platelets in a person’s blood is anywhere from 150,000 to 350,000 per microliter. PRP has many more platelets with their unique growth factors aimed at restoring normal blood flow to and healing of damaged tissue.
The question of dosage (how much, how often, what concentration) has been debated and studied by many different people. Finding the optimal treatment protocol has been quite a challenge. For one thing, platelet-rich plasma is being used for a wide number of problems and injected into different tissue types (e.g., tendons, ligaments, cartilage, bone).
This treatment approach is also being tried for acute (early) injuries as well as chronic (long-term) problems. It’s very likely that what works for one problem won’t necessarily be as successful as another condition affecting the musculoskeletal system.
Whether to use low, moderate, or high concentrations of PRP remains a point of debate. It is difficult to actually measure how many platelets are activated and delivered to damaged tissue. There is a concern that too much concentration would oversaturate the area and cause problems. And there is some evidence that high platelet levels create a threshold effect. This means that after a certain number of platelets (PRP concentration level), the effect is actually negative rather than positive.
Of course, too little concentration may not have the desired healing response. Studies comparing the effects of low to moderate to high concentrations of PRP remain at the stage of animal studies. Future studies with humans are still needed in this area.
As for the number of injections that work best, research results are limited because in most animal and human studies, only one injection has been used. The focus has been more on the timing of the injection. Some reports published showed better results when PRP injections were given during the first seven days after injury. So the chase has been on to find the ideal window for treatment by PRP injection. It may turn out that the timing is different for acute versus chronic tissue damage.
Experts suggest (based on evidence presented so far) that too high a concentration of PRP can lead to delayed wound healing and more scar tissue. Using two to three times the normal amount of platelets is a good place to start until further studies are done. It seems likely that maintaining a steady elevated level of platelets is a good idea. Waiting three to seven days between injections is advised right now.
The ideal or maximum number of injections may differ depending on the problem and the person. For now, it is suggested that acute ligamentous and tendinous injuries be treated with one to three injections. More chronic problems (arthritis) may benefit more from three to five injections.
There are no reported ill effects from platelet-rich plasma treatments but until more is known about the long-term effects, these guidelines are recommended.