Preparation of PRP
Platelet-rich plasma (Abbreviation: PRP) is blood plasma that has been enriched with platelets. As a concentrated source of autologous platelets, PRP contains (and releases through degranulation) several different growth factors and other cytokines that stimulate healing of bone and soft tissue.
The efficacy of certain growth factors in healing various injuries and the concentrations of these growth factors found within PRP are the theoretical basis for the use of PRP in tissue repair. The platelets collected in PRP are activated by the addition of thrombin and calcium chloride, which induces the release of these factors from alpha granules. The growth factors and other cytokines present in PRP include:
- platelet-derived growth factor
- transforming growth factor beta
- fibroblast growth factor
- insulin-like growth factor 1
- insulin-like growth factor 2
- vascular endothelial growth factor
- epidermal growth factor
- Interleukin 8
- keratinocyte growth factor
- connective tissue growth factor
There are, at present, two methods of PRP preparation approved by the U.S. Food and Drug Administration. Both processes involve the collection of the patient's whole blood (that is anticoagulated with citrate dextrose) before undergoing two stages of centrifugation (TruPRP) (Harvest) designed to separate the PRP aliquot from platelet-poor plasma and red blood cells. In humans, the typical baseline blood platelet count is approximately 200,000 per µL; therapeutic PRP concentrates the platelets by roughly five-fold. There is, however, broad variability in the production of PRP by various concentrating equipment and techniques.
In humans, PRP has been investigated and used as a clinical tool for several types of medical treatments, including nerve injury, tendinitis, osteoarthritis, cardiac muscle injury, bone repair and regeneration, plastic surgery, and oral surgery. PRP has also received attention in the popular media as a result of its use in treating sports injuries in professional athletes.
Results of basic science and preclinical trials have not yet been confirmed in large-scale controlled clinical trials. For example, clinical use of PRP for nerve injury and sports medicine has produced "promising" but "inconsistent" results in early trials. A 2009 systematic review of the scientific literature stated that there are few controlled clinical trials that have adequately evaluated the safety and efficacy of PRP treatments and concluded that PRP is "a promising, but not proven, treatment option for joint, tendon, ligament, and muscle injuries".
Proponents of PRP therapy argue that negative clinical results are associated with poor quality PRP produced by inadequate single spin devices. The fact that most gathering devices capture a percentage of a given thrombocyte count is a bias, since there is significant inter-individual variability in the platelet concentration of human plasma. More is not necessarily better in this case. The variability in platelet concentrating techniques may alter platelet degranulation characteristics that could affect clinical outcomes.
A 2014 Cochrane analysis found very weak (very low quality) evidence for a decrease in pain in those treated with platlet-rich therapies (PRT) from musculoskeletal injuries in the short term (up to three months). However, pooled data did not show a difference in function in the short, medium or long term. There was weak evidence that suggested that adverse events (harms) occurred at comparable, low rates in people treated with PRT and people not treated with PRT.
Implications for doping
Some concern exists as to whether PRP treatments violate anti-doping rules, such as those maintained by the World Anti-Doping Agency. It is not clear if local injections of PRP can have a systemic impact on circulating cytokine levels, in turn affecting doping tests; it is also not clear whether PRP treatments have systemic anabolic effects or affect performance. In January 2011, the World Anti-Doping Agency removed intramuscular injections of PRP from its prohibitions after determining that there is a "lack of any current evidence concerning the use of these methods for purposes of performance enhancement". In April 2014, Orioles first baseman Chris Davis, 28, underwent two PRP injections to speed the healing and recovery of an oblique injury. Left-hander Zach Britton had the procedure in his left shoulder in March 2012, according to the Baltimore Sun, and right-hander Dylan Bundy had the procedure last April before undergoing Tommy John surgery in June.
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