What is the role of PRP?

PRP stands for Platelet Rich Plasma. It is a term used very loosely to include anything that has growth factors and cytokines derived from blood (Platelets). When cells talk to each other they make proteins and peptides that are the messages that pass from one cell to another and determine how the cell will respond. These are called cytokines and include growth factors. Stem cells use these cytokines to control the actions of surrounding cells. Platelets store granules of these cytokines that can be harvested and used. A sample of blood is collected and centrifuged. The red blood cells collect at the bottom and the plasma containing platelets can be taken from the top. This plasma with platelets can be used as is or can be centrifuged a second time to concentrate the platelets at the bottom of the tube. We then have Platelet Rich Plasma (PRP) at the bottom and Platelet Poor Plasma (PPP) at the top. Collecting the PRP from the bottom it can be used as is or it can be activated by adding Calcium Gluconate. This causes a clot to form and the cytokines are then excreted by the platelets. The clot will slowly shrink as the cytokines are excreted. The platelets are now destroyed and because the clotting factors have been used up the plasma is now serum. The end product is cytokines in serum. This is obviously not PRP as there are no platelets and no plasma.

If the plasma containing platelets is injected into the body the platelets will be activated by contact with any tissue except endothelial cells (the cells that line arteries and stop platelets clotting). When this happens the cytokines will be released slowly over 5 or more days. This clot is known as Platelet Rich Plasma Gel (PRPG).

The normal role of platelets in the body is to adhere to any gap in blood vessels forming a clot to block the hole and releasing cytokines to heal the damage. It is this healing power that can be utilised by doctors to heal tendon, joint and other soft tissue injuries.

Ting Yuan et al, Augmenting tendon and ligament repair with platelet-rich plasma (PRP), Muscles Ligaments Tendons J. 2013 Jul-Sep; 3(3): 139–149


It is my hypothesis that this function of platelets can be used as a test to see if people will be responders or non-responders to stem cell therapy. We have tested this on a large number of patients using various combinations and the test has some usefulness.

Using Plasma/Platelets has not improved the results when given at the same time as stem cells but there may be some utility when given two weeks before stem cells and in the healing time after stem cell therapy.

Plasma/platelets vs stromal cells

Using the cytokines contained in platelets is like have a burst of stem cell activity. The results can last for one week in some patients whilst in others the results can be much longer lasting up to a year or more. There will be a group of patients who only need plasma/platelets and others who will need stromal cells (stem cells) to get lasting and complete effect.

Ting Yuan et al, Augmenting tendon and ligament repair with platelet-rich plasma (PRP), Muscles Ligaments Tendons J. 2013 Jul-Sep; 3(3): 139–149