Platelets, or thrombocytes, are tiny cell fragments in the blood that stop bleeding by clustering together to form a plug at the site of a damaged blood vessel, initiating the clotting process called hemostasis. Because platelets are constantly needed for patients with cancer, organ transplants, or severe trauma, they are collected using a specialized, highly efficient process called apheresis. This automated technique allows for the collection of a concentrated, therapeutic dose from a single donor, unlike whole blood separation.
Donor Eligibility and Preparation
Potential platelet donors must meet specific medical and physical requirements that are more stringent than those for standard whole blood donation. A donor must generally be in good health, be at least 17 years old, and meet a minimum weight requirement, typically 110 pounds. Before a donation can begin, a small blood sample is taken to ensure the donor has a sufficient platelet count and an acceptable hemoglobin level.
The minimum pre-donation platelet count must be at least 150,000 platelets per microliter of blood. Hemoglobin levels are checked to guard against donor anemia (minimums are 12.5 g/dL for females and 13.0 g/dL for males). Donors are also screened for certain medications, which is a difference from whole blood donation.
Aspirin and non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen are restricted. These drugs interfere with platelet function, making them ineffective for transfusion, so a donor must refrain from taking them for at least 48 hours before the procedure. Proper preparation also includes being well-hydrated and eating a low-fat meal, as excess fat can interfere with collection and testing.
The Platelet Collection Process (Apheresis)
The core method for collecting platelets is an automated procedure known as plateletpheresis or apheresis. This process uses a cell-separating machine to draw blood, separate the components, collect only the platelets, and then return the remaining blood components to the donor. This selective harvesting allows a single donation to yield a therapeutic dose equivalent to the platelets from several units of whole blood.
The donor is connected to the apheresis machine, usually through a needle placed in a vein in one arm, though a second needle may be used to return components faster. An anticoagulant, most commonly Acid Citrate Dextrose (ACD-A), is introduced into the blood as it leaves the body to prevent it from clotting within the machine’s tubing. This anticoagulant works by binding to calcium ions in the blood, which are essential for the coagulation cascade.
Blood enters a spinning bowl or chamber within the machine, where centrifugal force separates components based on their specific gravities. Red blood cells, being the heaviest, settle to the outer layer, while the lighter plasma remains closer to the center. Platelets and white blood cells settle into a middle layer known as the buffy coat.
A sensor within the machine identifies the buffy coat layer, allowing the device to selectively extract the platelet-rich portion. The remaining components, including red blood cells, most of the plasma, and white blood cells, are then safely returned to the donor. This process cycles repeatedly, drawing small amounts of blood, processing them, and returning the rest, until the target platelet yield is achieved. A complete apheresis donation typically takes between 60 and 90 minutes.
Post-Donation Care and Product Handling
Immediately following the procedure, the donor is instructed to rest for at least 15 to 20 minutes and consume fluids and a light snack. This period of rest helps the body adjust after the donation and prevents lightheadedness or dizziness. Donors are advised to drink an additional four 8-ounce glasses of non-alcoholic liquids over the next 24 hours to replenish fluids.
The anticoagulant, citrate, can lower blood calcium levels, causing a mild adverse reaction called citrate toxicity. Symptoms include a tingling sensation around the lips, nose, or fingers, which can be managed by slowing the donation rate or administering oral calcium supplements. Donors must also avoid heavy lifting or strenuous activity for the remainder of the day to prevent bruising or bleeding at the needle insertion site.
Once collected, the platelet product requires specialized handling. Platelets must be stored at room temperature, specifically between 20°C and 24°C, to maintain their viability and function. Unlike other blood components, they must also be kept under constant gentle agitation to prevent clumping and ensure proper gas exchange.
Because this storage temperature is ideal for bacteria, platelets have an extremely short shelf life (typically five to seven days), posing a major logistical challenge. To enhance safety, some collected units undergo pathogen reduction technology (PRT), a process that inactivates viruses, bacteria, and parasites in the product. The combination of short shelf life and constant patient demand necessitates that donors give platelets more frequently than whole blood donors.