Introduction: Platelet-Rich Plasma (PRP)
Men and women who are considering hair transplantation are likely to research the subject first, including search of the World Wide Web. A Web search of “hair transplantation” and related terms may turn up references to “platelet-rich plasma” or its acronym PRP, described as a procedure to enhance healing and hair growth after hair transplantation. Abundant references can be found to use of PRP in sports medicine to enhance healing after injury. Some Web articles make extravagant claims for PRP.
How is PRP used in hair transplantation? What is its purpose? Does it really contribute to better healing and hair growth after transplantation surgery?
Hair transplantation today is often performed in a single “megasession”, or in multiple sessions over a period of weeks or months. A megasession completes the entire procedure—harvest of hair follicles from a donor site at the back of the patient’s scalp and placement of harvested follicles in a recipient site on the scalp—in a single session lasting several hours. Multiple sessions may be a better choice for some patients, based on a patient’s wishes and factors such as medical conditions.
Over the ensuing 3 to 6 months after transplantation, most transplanted follicles will thrive and produce hair at their new site. Some transplanted follicles will fail to thrive in their new environment.
Search for a way to enhance survival of transplanted hair follicles and promote healing with minimal scarring after transplantation led to trials of PRP. A growing literature already existed on use of PRP in sports medicine, orthopedic surgery and dental surgery and a number of other medical and surgical specialties to enhance tissue repair and healing after surgical procedures or injury.
Exploration of questions about PRP may best begin with a look at platelets, the centerpiece of platelet-rich plasma.
What Are Platelets?
Platelets are biological constituents of blood, along with red and white blood cells. Unlike red and white blood cells, platelets do not have a nucleus and therefore do not qualify to be called “cells”. They are somewhat smaller than red and white blood cells.
Platelets are probably best known as components of the blood clotting system. When injury disrupts a blood vessel and causes bleeding, platelets are quickly activated and contribute to formation of a clot that stems the flow of blood. Platelets contribute to clot formation by (1) participating in release of a cascade of chemical factors essential to the clot-forming process, and (2) changing shape and interlocking with one another to plug the bleeding site by forming a physical barrier to blood flow. This physical barrier consists of interlocked platelets and strands of hemostatic fibers called fibrin.
But platelets are more than just first-line responders to bleeding injury. Every platelet is also a biochemical storehouse of regulatory, signaling and growth-factor molecules that participate in recovery and healing of tissue as well as emergency response to injury. Growth-factor molecules associated with platelets include:
- Platelet-derived growth factor (PDGF)—promotes blood vessel growth, cell replication, skin formation;
- Transforming growth-factor-beta (TGF-b)—promotes growth of matrix between cells, bone metabolism;
- Vascular endothelial growth factor (VEGF)—promotes blood vessel formation;
- Epidermal growth factor (EGF)—promotes cell growth and differentiation , blood vessel formation, collagen formation;
- Fibroblast growth factor-2 (FGF-2)—promotes growth of specialized cells and blood vessel formation; and,
- Insulin-like growth factor (IGF)—a regulator of normal physiology in nearly every type of cell in the body.
All of these growth factors initiate and enhance physiologic processes that contribute to tissue recovery and health after injury. The growth factors are also involved in normal physiologic processes such as blood vessel formation.
The rationale for use of PRP in surgery is to artificially increase the number of platelets at a site where the storehouse of growth factors in the platelets can be put to use in enhancing tissue recovery, repair and health.
What is PRP?
PRP is blood plasma containing a concentration of platelets many times greater than occurs normally in blood. PRP is “autologous”, meaning that it comes from the patient’s own body. This is similar to the practice of having a patient donate his/her own blood before a surgical procedure, to be used in preference to blood from the hospital blood bank should a transfusion be needed. Another example is the removal and transplantation of a patient’s own skin for a plastic surgery procedure. Because PRP is autologous, it has no potential for causing a foreign-body immunologic reaction. PRP is immunologically neutral.
PRP in Sports Medicine
PRP has gained increasing attention in sports medicine due to its use in treating muscle, bone and joint injuries of high-profile professional athletes. Sports stars treated with PRP include Pittsburgh Steelers receiver Hines Ward, Takashi Saito of the Los Angeles Dodgers and Jose Reyes of the New York Mets. In each of these athletes, PRP is credited with hastening recovery from injury without need for surgery.
As use of PRP in sports medicine is becoming more widespread, there are also increasing cautionary warnings about uncritical acceptance of PRP as a “wonder cure”. While the outcome of PRP treatment is often positive, there is still a lack of unbiased scientific data from controlled clinical trials in which PRP treatment is objectively compared with other treatments for the same condition.
PRP in Orthopedics and Other Medical Specialties
PRP is also finding increasing use in orthopedics, dental implant surgery and other surgical specialties as a wound treatment. Safe use of PRP has been documented in neurosurgery, ophthalmology, urology, cardiac surgery, thoracic surgery, maxillofacial surgery and cosmetic surgery. Approval of these uses by the U.S. Food and Drug Administration (FDA) is not required as long as the use is procedural and part of the treatment process, and no advertised claims of its efficacy are made. The American Academy of Orthopaedic Surgery (AAOS) has noted editorially that, while PRP can be valuable in enhancing soft-tissue repair, bone growth and wound healing, more research is needed to define the circumstances in which use of PRP is clinically justified. PRP use is not appropriate in all patients, the AAOS noted.
PRP in Historical Perspective
Techniques for producing platelet-rich plasma (PRP) and using it to promote and enhance healing after tissue injury have been known for more than 30 years. For most of that period, uses of PRP were in hospitalized surgical patients. Few comparative studies of significant size or good design were carried out. Use of PRP was limited by technical difficulties of producing PRP preparations of adequate potency.
Advances in technology have made the preparation of PRP faster and more efficient, and increasing uses of PRP began to be found in surgical specialties. Surgical hair restoration was one of the specialty areas in which PRP began to be used.
How PRP is Made
Platelets for PRP are derived from a patient’s own blood:
- Blood is withdrawn from a patient’s arm by syringe, as it would be for any laboratory procedure.
- The tubes containing withdrawn blood are placed in a centrifuge and spun for a period of time.
- The centrifuging “spins down” the red and white blood cells and platelets and concentrates them at various levels in the tubes. Blood plasma that is rich in platelets is drawn off from the appropriate level. Plasma defined as platelet-rich plasma contains 4 to 8 times the number of platelets per cubic centimeter found in normal plasma. With a little additional preparation the PRP is ready for application.
PRP in Hair Transplantation
The potential for using PRP to promote healing and hair growth after hair transplantation is centered in three functional applications:
- To preserve and enhance hair follicle viability during and after hair transplantation;
- To promote and enhance tissue repair and healing after hair transplantation; and,
- To reinvigorate dormant hair follicles and stimulate new hair growth.
To Preserve and Enhance Hair Follicle Viability
Between the time that hair follicles are removed from a donor area of the scalp and transplanted into a recipient area, they are subject to damage from several causes:
- Dehydration if the donor follicles are inadequately moistened between the times of removal and transplantation;
- Oxygen and nutrient starvation due to being removed from blood supply during the harvest-to-transplantation time period;
- Temperature and acid/alkaline changes in the follicle environment; and,
- Revascularization injury when the donor follicles are transplanted to the recipient site and must re-adapt to having a blood supply.
A common approach to maintaining donor hair follicle viability during the transition period is to keep them in a storage solution that provides a protective environment of appropriate temperature, chemical balance and nutrient supply. Recent research has indicated that addition of PRP to the storage solution improves follicle viability during and after transplantation, enhances post-transplantation tissue healing and promotes hair growth in transplanted follicles. An approach advocated by some investigators is to bathe the donor hair follicles in activated PRP just prior to transplantation.
Investigators have reported that PRP promotes hair growth from follicles by the action of platelet growth factors on hair follicle stem cells. The platelet growth factors induce follicle stem cells to shift from a dormant state to an active state that starts the process of hair production. While investigators have reported such activity, no advertised claims of PRP efficacy in promoting hair growth can be made because there has been no FDA approval that would allow such claims to be made.
To Promote and Enhance Tissue Repair and Healing
In activity promoting tissue repair and healing after injury of surgery, the growth factors stored in platelets are released at a site of tissue injury, promoting tissue repair and healing. Individual growth factors such as PDGF have been used by surgeons to promote wound healing in hospitalized surgical patients. The rationale for using PRP in outpatient surgical hair restoration is to use the full array of platelet-associated growth factors to promote healing and minimize scar formation, as well as to promote maximum hair growth in transplanted follicles.
A described method of applying PRP to scalp incisions is by injection of a PRP gel into the wounds at the time of wound closure. Clinicians and investigators using this procedure have described enhanced healing at the transplant site. These reports are usually of individual cases or of a small number of cases. Such reports do not meet definitions of clinical trials that would, for example, be required in the United States for seeking FDA approval of PRP use specifically in hair transplantation with claims of efficacy and safety. Some investigators suggest that PRP should not be used routinely in hair transplantation to promote healing, but might be of use in patients who have had previous injury or scarring at a transplant site. Investigators who oppose routine use of PRP in hair transplantation cite the need for additional data from well-designed clinical trials.
To Reinvigorate Dormant Hair Follicles
After noting enhanced hair growth of transplanted hair after use of PRP, investigators conducted a small study of PRP effect on dormant non-transplanted hair follicles. The study hypothesized that platelet growth factors can “wake up” dormant hair follicles and begin the production of new hair. PRP was applied after scalp skin was slightly injured to induce platelets to release growth factors at the injury site. Enhanced hair growth and hair diameter was noted over the next 4 months, with a fall-off in enhanced hair growth after 4 months. This use of PRP is still regarded as experimental, with need for further study.
Safety, Complications, Contraindications to Use of PRP
PRP is immunologically neutral and poses no danger of allergic, hypersensitivity or foreign-body reactions.
Sterile technique must be used at every stage of PRP preparation and application. Sterile technique is especially important if a patient has an underlying medical condition that predisposes to infection.
A brief period of inflammation at wound sites may be experienced by a patient after application of a PRP gel. Inflammation may be associated with release of platelet-associated factors at the wound site.
Some medical conditions may be a contraindication to use of PRP. Many of these are not absolute contraindications because the conditions vary from patient to patient. It is wise to raise the question with a physician hair restoration specialist if and when the use of PRP is discussed.
Is PRP Approved by the United States FDA?
The use of PRP in the United States as part of the clinical process of hair transplantation does not require FDA approval, just as the use of blood transfusion during or after surgery does not require FDA approval. Use of PRP as part of the surgical treatment is defined as a procedure and is not subject to FDA regulation.
However:
- In the United States, the device used to prepare PRP must have FDA approval. Centrifuges that separate PRP from whole blood for a medical purpose (e.g., to assist tissue healing) are medical devices covered by the Federal Food, Drug and Cosmetics Act. Federal law requires that manufacturers of medical devices must obtain clearance or approval for the products before offering them for sale. Failure to have premarket approval or clearance for such devices is a violation of U.S. law. Premarket approval requires data showing that a device is safe and effective.
- The FDA has not approved PRP as a medication specifically for use in hair transplantation. FDA approval would be based on objective evidence of efficacy (e.g., promoting healing, promoting hair growth) and safety. Claims that PRP is “FDA approved” for use in hair transplantation are incorrect. Advertised claims of PRP efficacy in promoting hair growth may be a violation of FDA protocol regarding medical claims.
The use of PRP specifically in hair transplantation to promote healing and hair growth could be considered when, for example:
- Clinical trials of appropriate size and design are approved by the FDA, and
- Results from the clinical trials convincingly demonstrate that end-point goals of efficacy and safety have been met.
Bibliography
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Sampson S, Gerhardt M, Mandelbaum B. Platelet rich plasma injection grafts for musculoskeletal injuries: a review. Current Review of Musculoskeletal Medicine 2008; Dec. 1 (3-4) 165-174.
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