Platelet-Rich Plasma (PRP) is a regenerative treatment that uses a concentration of a patient’s own platelets to stimulate healing in damaged tissues. The therapy begins with a simple blood draw, followed by specialized preparation to isolate and concentrate the therapeutic components of the blood. Platelets are small blood cells recognized for their role in clotting, but they also contain numerous growth factors that promote tissue repair, cell growth, and the formation of new blood vessels. By concentrating these platelets to levels significantly higher than found in normal blood, PRP aims to enhance the body’s natural healing response for conditions like tendon injuries, arthritis, and hair loss.
The Critical Role of Anticoagulants in PRP Preparation
The primary challenge in preparing Platelet-Rich Plasma is preventing the blood from clotting immediately after it is drawn from the body. Blood rapidly begins its natural coagulation cascade when it comes into contact with a foreign surface, which would trap the platelets in a solid clot and make them unusable for injection. To keep the blood in a fluid, liquid state during the processing steps, an anticoagulant must be introduced into the collection tube.
The most commonly recommended anticoagulant specifically for PRP preparation is Acid Citrate Dextrose (ACD), often used as Formula A (ACD-A). Citrate prevents clotting by binding to calcium ions in the blood, which are necessary cofactors for the coagulation cascade. Dextrose is included to provide metabolic support for the blood cells, helping to maintain their viability during preparation. ACD is favored because it preserves the structural integrity and functionality of the platelets, ensuring they remain ready to release their growth factors once injected.
Another citrate-based option is Sodium Citrate, which also acts by chelating calcium to prevent clotting. Some specialized kits using Sodium Citrate have been associated with decreased clinical efficacy compared to ACD-A systems, leading many practitioners to prefer ACD-A. The choice of anticoagulant directly impacts the quality and therapeutic potential of the final PRP product.
Anticoagulants routinely used for other laboratory blood tests are avoided for PRP due to their negative effect on platelet function. For example, Ethylenediaminetetraacetic acid (EDTA) is an effective anticoagulant, but it can negatively affect the platelet membrane and compromise their ability to release growth factors. Similarly, Heparin can interfere with platelet function and may inhibit the activity of certain growth factors, making it less suitable for a regenerative product.
Tube Color and Kit Variability
The answer to which color tube is used for PRP is not a single color, as it depends on whether a standard phlebotomy tube or a specialized commercial kit is employed. In the traditional system of vacuum blood collection tubes, the color of the tube stopper indicates the additive inside. Tubes containing sodium citrate, which is one of the acceptable anticoagulants, are typically light blue in the standard phlebotomy system, but these tubes are primarily designed for coagulation testing, not necessarily for optimal platelet recovery.
For PRP, the most common collection vessel is a specialized, proprietary tube that often follows a unique color code or label, frequently appearing as yellow or gold. These specialized tubes are optimized for the platelet concentration process and usually contain the preferred anticoagulant, ACD-A. The yellow or gold color often signifies the presence of a gel separator at the bottom of the tube. This polyester or silicone gel has a specific density that, after spinning, forms a stable barrier between the heavier red blood cells and the lighter plasma components, facilitating the precise collection of the platelet-rich layer.
The use of a proprietary kit means the tube color may deviate from standard clinical lab colors; therefore, the anticoagulant is the most reliable indicator of suitability, not the cap color. Regardless of the external color, a tube intended for high-quality PRP must contain a citrate-based anticoagulant, such as ACD or sodium citrate, to prevent premature clotting and maintain platelet integrity. The presence or absence of a separation gel is another design element that distinguishes specialized PRP tubes from standard blood collection tubes.
From Whole Blood to Plasma: The Separation Process
Once the blood is collected into the specialized tube containing the anticoagulant, the mechanical process of separation, known as centrifugation, begins. Centrifugation involves spinning the tubes at high speeds to separate the blood components based on their density. Whole blood separates into three distinct layers: the heaviest red blood cells settle at the bottom, the plasma (the liquid component) remains at the top, and a small, thin layer known as the buffy coat, which contains the concentrated platelets and white blood cells, forms in the middle.
Single-Spin Protocol
The specific protocol used for spinning the blood influences the final concentration and quality of the PRP. A single-spin protocol involves one round of centrifugation, which separates the red blood cells and leaves a mixture of platelet-rich plasma and platelet-poor plasma in the upper layer. This method is faster and simpler but typically results in a lower concentration of platelets, usually two to four times the baseline level.
Double-Spin Protocol
A double-spin protocol is a more advanced technique that involves two sequential rounds of centrifugation. The first spin separates the red blood cells at a lower speed to keep the platelets suspended in the plasma. The plasma is then transferred to a second tube and spun again at a higher speed. This second spin pellets the platelets at the bottom of the new tube, allowing the removal of the excess platelet-poor plasma and resulting in a much higher concentration of platelets, often five to eight times the baseline.