Joost Peerbooms

28 Chapter 2 Preparation Protocols Besides a large heterogeneity in the concentrations of platelets, leukocytes, and growth factors between systems, the preparation protocols for the different systems also differed largely. Wide ranges were found for both the centrifugal force (350-2008g) and the total centrifugation time (5-21 minutes). There are many ways of preparing PRP; the most common methods are the plasma-based and buffy coat-based methods. 29 Although not known for all systems in this review, most systems use the buffy coat- based method. As mentioned earlier, buffy coat-based systems produce PRP with a high concentration of leukocytes, as the buffy coat is rich in leukocytes. 11,15,50 Although the ideal concentrations of blood components and growth factors for the specific fields of application have yet to be determined, the field of application should play an important role in the choice for the most appropriate PRP separation system. Other factors such as the volume of whole blood needed, the final volume of PRP, and the usability and reliability of the separation system could also be taken into consideration. Finally, the price of the systems can be taken into consideration, as a wide variation in price per kit ($95-$500) was found. Strengths and Limitations This is the first systematic review that offers a comprehensive overview of the concentrations of blood components in PRP produced by all the commercially available PRP separation systems and that analyses the differences between the systems in terms of the concentrations of blood components and growth factors. Initially, this study was designed as a meta-analysis. Unfortunately, despite all the authors who were contacted, we had to deal with a lot of missing data, and no raw data were available for the majority of the studies. This limited the statistic options available for analysing the differences between systems, and therefore, a meta-analysis could not be conducted. To overcome the missing data, descriptive results of the studies that compared 2 PRP preparation systems were summarized. Furthermore, the number of samples studied in the included studies was rather small; only 5 of the 19 studies used 20 samples, and 10 of the 19 studies used 10 samples, which also limits a comparison between systems. However, as this review of the literature showed, future research on the components of PRP should not focus on the concentrations of the components but rather on the optimal concentrations of platelets, leukocytes, and growth factors for the different fields of application. The use of leukocyte-rich PRP in chronic tendinopathy has been extensively investigated and been proven to be superior to leukocyte-poor PRP. 20 For other applications, osteoarthritis, for example, the evidence is limited, and well- designed clinical studies are necessary to gain more insight to which formulation of PRP is most suitable. In conclusion, this review demonstrates that there is a large heterogeneity among different systems with regard to the concentrations of platelets, leukocytes, and growth