Platelet rich plasma (PRP) therapy is a modality which utilizes the innate healing potential of autologous platelets to treat a wide variety of aesthetic and musculoskeletal conditions. Hematologists first experimented with PRP therapy in the 1970’s to treat thrombocytopenia (low platelet count). Since, the practice of concentrating and reintroducing platelets has expanded to include the treatment of a wide variety of conditions including knee osteoarthritis, epicondylitis and androgenic alopecia. Improving patient outcomes with PRP depends upon administering an adequate concentration of platelets into damaged or weakened tissues. Commercially available kits stratify blood elements and concentrate platelets with centrifugation. Some kits rely on a single spin while others apply two rounds of centrifugation to separate platelets from other blood elements. This article discusses the key differences between single and dual spin preparation methods.
Principles of PRP Preparation
At it’s foundation, achieving results in PRP therapy requires clinicians to adequately concentrate platelets. Successfully preparing platelet rich plasma is a highly variable process. The process unfolds in four fundamental steps; blood draw, centrifugation, activation, and administration (via injection or topical application). Platelet concentration is achieved during the centrifugation process which stratifies the various blood components by weight. The heaviest blood elements travel at a faster rate and settle beneath the lighter elements. After the initial centrifugation, erythrocytes (red blood cells) settle below a supernatant which is composed of white blood cells, platelets and plasma.
Single v. Double Spin: Platelet Concentration
Third party research conducted by BioSciences Research Associates (BSR) reveals the primary difference between single and dual centrifugation is platelet concentration. Double spin kits have the potential to yield highly concentrated PRP, while single spin designs result in a serum with less platelets than whole blood (technically platelet poor plasma). Product analysis was conducted by Robert Mandle, PhD, who lead a team at BSR in 2016 to compare platelet concentration amongst a selection of commercially available PRP kits.¹
BSR is an independent contract research laboratory located in Cambridge and once academically affiliated with Harvard Medical School. BSR is currently affiliated with the Immune Disease Institute at Harvard and as such draws from a community of nearly 400 bioscience researchers. The BSR laboratory complies with the Food and Drug Administration’s (FDA) Current Good Manufacturing Practice (cGMP) to assist pharmaceutical and biotech companies in product development and clinical trial support.
Principles of Single Spin PRP Kits
Commercially available single-spin kits such as Eclipse and Regenkit rely on a soluble polymer to stratify blood elements. The polymer has a specific density between platelets and red blood cells. Upon centrifugation, the gel polymer creates a physical barrier which effectively isolates red blood cells, creating a serum with low hematocrit levels. According to third party research, Eclipse PRP and Regenkit produce PRP with 0.0% hematocrit levels. The complete removal of red blood cells eliminates the potential for an inflammatory response which occurs when red blood cells are introduced outside of vascular pathways. Though RBCs are successfully eliminated, these single spin kits produce a serum with a platelet concentrations less than that of whole blood, also known as platelet poor plasma (PPP).
Principles of Dual Spin PRP Kits
Dual spin centrifugation kits apply radial force to stratify blood elements and concentrate platelets up to 6.7 times that of whole blood. Blood is drawn in the presence of an anticoagulant which prevents platelet activation during the mechanical stress of centrifugation. The sample is spun according to the manufacturer’s recommendations and the resulting supernatant is collected for a second spin. The supernatant contains plasma, platelets, white blood cells and a slight collection of red blood cells. The second round of centrifugation is another opportunity for platelets still suspended in plasma to fall out of solution and results in a highly concentrated PRP.
Why are Single Spin Methods Less Effective at Concentrating Platelets?
Single spin kits may have the appeal of a more streamlined process, but according to third party analysis, these kits simply don’t concentrate platelets. The gel polymer at the center of the single spin process only targets platelets of a specific density. Though the exact material utilized within gel separator kits is unknown, we can speculate this substance has a specific density just above red blood cells, given the exceedingly low hematocrit levels achieved with single spin kits. This process is only able to capture platelets which correspond to the density of the polymer, when, in actuality, platelet density falls along a wide spectrum. This results in a majority of the patient’s platelets being left behind.
Platelet Concentration and Patient Outcomes
By definition platelet rich plasma is a serum which contains platelets at a higher concentration than whole blood. Successful PRP therapy harnesses the healing capacity of platelets by reintroducing these non nucleated cell fragments into damaged or aging tissues. Platelets are activated in the presence of calcium. The activation process occurs naturally when platelets are exposed to collagen, though certain situations benefit from preemptive activation with calcium chloride. Once activated, platelets degranulate and start to release tiny bioactive molecules known as growth factors. Growth factors signal surrounding cells to increase migration and proliferation. Platelet derived growth factor, vascular endothelial growth factor, insulin growth factor-1 & 2, epidermal growth factor, and transforming growth factor-β act in complex ways to regulate angiogenesis, mesenchymal stem cell mitosis, protein synthesis, osteoblast formation, collagen synthesis, and cartilage regeneration.
There is tremendous potential for regeneration when a significant concentration of platelets is introduced into damaged tissues. Major adverse events are unheard of and there is no risk of allergic reaction because the therapy utilizes the patient’s own blood. While there is ample level I evidence supporting the use of PRP therapy, a complete review of the literature would reveal inconsistent findings. Many of these inconsistencies can be traced back to fundamental differences in PRP preparation (and administration) processes, which are continually refined. According to third party research, the dual centrifugation method yields PRP with significantly higher platelet concentration compared to the single spin method. As such, dual spin kits have the potential to improve patient outcomes by introducing significantly greater platelet concentrations.