Platelet-Rich Plasma (PRP) has been banned in competitive athletes because some people think it may enhance athletic performance. However, there is very little published research to support or undermine this point of view. The purposes of this study are: (1) To assess the effects of local platelet-rich plasma (PRP) therapy on systemic levels of growth factors with suspected or known performance-enhancing effects; and (2) To understand whether the effect of PRP therapy on these growth factors differs between intramuscular and intratendinous PRP injections.

This research study is looking for 40 people who are receiving platelet-rich plasma therapy for a tendon or muscle injury. The study involves collecting seven blood samples (2 teaspoons each) from each patient, before and after the PRP treatment. Blood samples may be donated at any location of the patient's choosing, and participants will be paid for their time.

To understand the short-term systemic effects of local PRP injections, we will measure the serum concentrations of six growth factors before and during the four days following PRP injection: human growth hormone (hGH), IGF-1, basic FGF, PDGF-BB, VEGF, and IGFBP-3. These molecules are of particular interest because they may have stimulatory effects that enhance athletic performance, and because they have been banned in competitive athletes by the World Anti-Doping Agency (WADA).

We aim to recruit 40 patients who are receiving ultrasound-guided intratendinous (IT) or intramuscular (IM) PRP injections. Blood will be drawn immediately before (baseline); 15 minutes after; and 3, 24, 48, 72 and 96 hours after receiving PRP therapy. A fraction of the therapeutic PRP preparation will be isolated for growth factor analysis. Serum concentrations of growth factors will be quantified by ELISA. Statistical analyses will be conducted to assess the change in each growth factor following PRP injection. To understand the impact of injection site on systemic growth factors, changes in concentration will also be compared between the intratendinous and intramuscular groups.

Study subjects will participate in the following steps: (1) Initial diagnostic visit with Orthopaedic Surgeon, (2) Blood collection as part of PRP therapy, (3) Ultrasound-guided PRP therapy administered by Stanford radiologist, and (4) Blood collection for the study. Steps (1) through (3) are all part of the standard of care, which the patient will have chosen independently of the study. In step (4), blood samples will be collected by venipuncture at various time points and assayed for growth factor concentrations. Less than 10 mL (2 teaspoons) of blood will be collected at each of seven time points over five consecutive days. In order to minimize inconvenience to the patient we will meet patients at a location of their choosing, such as the patient's home or office, for blood collection on days 2-5. Participants will be compensated after all seven blood samples have been donated.

Inclusion Criteria:

• Male and female patients 18-50 years old, receiving ultrasound-guided intratendinous or intramuscular PRP injections

Exclusion Criteria:

• History of cancer, diabetes, hormone-replacement therapy, or abnormal nutritional habits.
• Contraindications for PRP therapy itself:
  • preexisting coagulation defects including thrombocytopenia
  • hypofibrinoginemia
  • anticoagulation medications
  • hypersensitivity to bovine products, which may be used for platelet activation.