Growth factor release from LP-PRP system preparations. Growth factor release from LP-PRP system preparations. Bars represent the mean ± SD of the fold change in serum growth factor content of LP-PRP activated with CaCl2 (blue bars; n=5 donors) or exogenously with CaCl2 + thrombin (red bars; n=7 donors). *p<0.03 compared with whole blood. **p<0.01 compared with whole blood. The green line represents whole blood platelet growth factor levels (set to 1-fold for comparison). LP-PRP, leucocyte-poor platelet-rich plasma. William R Parrish et al. BMJ Open Sport Exerc Med 2016;2:e000071 ©2016 by BMJ Publishing Group Ltd