Here’s the skinny on the two best-known blood treatments: RegenokineHow it works:1. The doctor draws your blood into a syringe that contains small glass beads treated with a chemical called chromium sulfate. 2. The mixture gets incubated for 24 hours and then spun in a centrifuge to separate its parts. 3. Several naturally occurring anti-inflammatory proteins, including one called interleukin-1 receptor antagonist, become separated from the blood and are extracted.4. Over the course of several days, the blood proteins get injected into your affected nerve or joint, where they (presumably) will act as powerful anti-inflammatory agents.Results: In one trial, two-thirds of patients had as much as 50% less pain 2 years out. But a similar study found the drug to be only minimally more effective than a placebo.Available: Dusseldorf, Germany; Los Angeles; Miami; New York CityPrice tag: $675-$9,000Covered by insurance? DoubtfulWho’s used it: Kobe Bryant (arthritic knee); Willie Nelson (torn rotator cuff); Alex Rodriguez (knee and shoulder injuries); Pope John Paul II (arthritis) MORE: 100 Little Tips And Tricks To Ease Your Pain   Platelet-Rich Plasma (PRP)How it works:1. Blood is drawn from your arm and spun in a centrifuge to single out platelets, small blood cells that create healing clots and release chemicals called growth factors that speed healing. 2. The extracted platelets and other blood components are injected into the troubled joint or muscle to work their magic. (Additional injections may be needed after follow-up visits.)Results: In a study of 50 patients with arthritic knees, PRP led to significant improvements in pain a year later. In another study, those who got PRP injections showed no more improvement than a group shot up with a standard joint lubricant.Available: At doctors’ offices in all 50 US statesPrice tag: $500-$1,100Covered by insurance? Rarely if ever; might change as the treatment becomes more commonWho’s used it: Rafael Nadal (knee tendinitis); Tiger Woods (postsurgical knee pain); Troy Polamalu (strained calf) MORE: The Ultimate Pain-Fighting Workout