Platelet Donation
After a short physical examination, the donor is taken into the donation room and sits in a chair next to the machine. The technician cleans one or both arms with iodine, or other disinfectant, and inserts the catheter into a vein in the arm. With some procedures both arms are used, one to draw blood and the other to return it. The process takes about one to two hours while blood is pulled into the machine, mixed with an anticoagulant such as sodium citrate, spun around, and returned to the donor. "Double needle" procedures using both arms tend to be shorter since the blood is drawn and returned through different catheters; with "single needle" procedures a set volume is drawn and processed in the first part of the cycle and returned in the second part. The donor's blood undergoes repeated cycles of draw and return.
Side effects of the donation of platelets generally fall into three categories: blood pressure changes, problems with vein access, and effects of the anticoagulant on the donor's calcium level. Blood pressure changes can sometimes cause nausea, fatigue, and dizziness. Venous access problems can cause bruising, referred to as a hematoma. While donating, a supply of calcium antacid tablets is usually kept close by to replenish the calcium lost. Because the anticoagulant works by binding to the calcium in the blood, a donor's levels of calcium - and especially of active calcium ions - drop during the donation process. The lips may begin to tingle or there may be a metallic taste; since calcium enables the function of the nervous system, nerve-ending-dense areas (such as the lips) are susceptible, at least during the donation process. Unusually low calcium can cause more serious problems such as fainting, nerve irritation and short-duration tetany. Such an acute hypocalcaemia is usually due to low calcium levels prior to donation, aggravated by the anticoagulant. Hypocalcaemia can be curtailed by modestly increasing dietary calcium intake in the days prior to donation. Serious problems are extremely rare, but apheresis donors are typically not allowed to sleep during the long donation process so that they can be monitored.
Aside from the procedure, donating platelets is different from donating blood in a few ways.
Firstly, the donor must not take aspirin or other anti-platelet medications such as such as clopidogrel (Plavix) for anywhere from 36 to 72 hours prior to donation. (Guidelines vary by blood center.) The reason is that aspirin can prevent platelets from adhering to clot bleeding. Some blood centers also prohibit the taking of any NSAID (non-steroidal anti-inflammatory drug) for 36 hours prior.
Secondly, one is generally allowed to donate platelets anywhere from every 3–28 days. This is a stark contrast to whole-blood donation, which has an eight-week (or longer) waiting period between donations. Along those lines, since platelet donation does temporarily remove whole blood from the body, it may be necessary to wait eight weeks after a whole blood donation to donate platelets, although one week is more common. In the US, a donor is only allowed to donate 24 times each year and may not lose more red blood cells or plasma in a year than they would from the maximum allowable number of whole blood donations.
Thirdly, additional tests may be required before becoming a donor for the first time. These tests may establish a platelet count. Newer automated platelet pheresis machines do that as the donation begins, and adjust accordingly the quantity of platelets to be drawn. Tests may also determine the donor's compatibility with particular recipients through an HLA (Human Leukocyte Antigen) test. Multiparous women may be excluded from becoming donors due to heightened TRALI risk. These tests usually involve nothing more involved than the drawing of several tubes of blood.
Read more about this topic: Plateletpheresis