Platelets are minute, colorless cell fragments that circulate in the bloodstream. Their primary function is to initiate hemostasis, the process of stopping bleeding, by forming a plug or clot at the site of a damaged blood vessel. When a vessel is injured, platelets adhere to the lining and aggregate to form a temporary seal.
The demand for these components is constant because platelets have an extremely short shelf life, typically surviving for only five to seven days after donation. Patients undergoing aggressive treatments like chemotherapy often suffer from low platelet counts, a condition called thrombocytopenia. Platelet transfusions are also routinely required for victims of severe trauma, patients undergoing organ transplants, and those having complex surgeries.
Donor Eligibility and Pre-Screening
Before an individual can donate platelets, they must pass specific health requirements designed to protect both the donor and the recipient. Donors must be in generally good health, meet a minimum age requirement, typically 17 years old, and weigh at least 110 pounds.
The pre-screening process begins with a detailed health questionnaire and a physical assessment that includes checking vital signs like temperature, pulse, and blood pressure. A small blood sample is taken via a finger stick to confirm the donor’s hemoglobin level and current platelet count. The platelet count must be sufficiently high to ensure a successful donation yield while leaving enough circulating platelets for the donor’s own safety.
A specific restriction involves certain medications, particularly non-steroidal anti-inflammatory drugs (NSAIDs) like aspirin and ibuprofen. Since these drugs interfere with the ability of platelets to clump together, a donor must refrain from taking them for at least 48 hours before the procedure. This precaution ensures the donated platelets will be fully functional and effective for the patient receiving the transfusion.
The Platelet Aphaeresis Procedure
The actual collection process is called platelet aphaeresis, a specialized form of automated donation that selectively separates blood components. The procedure requires the donor to be comfortably seated for an extended period, typically between 90 and 120 minutes. This prolonged time commitment is necessary because the machine must process a significant volume of blood to harvest an adequate quantity of platelets.
A sterile, single-use kit connects the donor to the apheresis machine, which operates through a continuous-flow system. Blood is withdrawn from one arm and enters a centrifuge within the machine that spins the blood at high speeds. This centrifugal force separates the blood into layers based on density, allowing the machine to isolate the platelets and a small amount of plasma for collection.
To prevent the blood from clotting inside the machine and tubing, an anticoagulant, usually a solution containing citrate, is mixed with the blood as it is withdrawn. Once the platelets are collected into a separate bag, the remaining blood components—primarily red blood cells and most of the plasma—are safely returned to the donor, often through a needle in the same arm or a separate needle in the opposite arm. The use of a second needle allows for a faster, more efficient procedure.
Recovery and Donation Frequency
Following the completion of the aphaeresis procedure, the donor is advised to rest briefly and consume fluids and a snack. Because the red blood cells are returned to the donor, physical recovery is generally fast, with the body rapidly replacing the small volume of collected plasma and the donated platelets. Donors should avoid heavy lifting or strenuous arm use for a few hours to minimize the risk of bruising at the needle insertion site.
A common, though temporary, side effect is a mild reaction to the citrate anticoagulant, which can temporarily bind calcium in the donor’s blood. This can manifest as a tingling sensation around the lips, nose, or fingertips, but it is easily managed by slowing the donation rate or by giving the donor a calcium supplement. Bruising at the venipuncture site is another minor possibility, but serious adverse reactions are rare.
The targeted nature of aphaeresis allows for a more frequent donation schedule compared to traditional whole blood donation. Platelets can be safely donated as often as every seven days, though most blood centers limit the total number of donations to 24 times within a 12-month period. The body’s platelet count typically returns to baseline levels within seven days, whereas whole blood donors must wait a minimum of 56 days between donations.