Plateletpheresis is a special type of blood donation that allows the blood transfusion that only transfers platelets, the cells that cause blood clotting, and sometimes, a small amount of unwanted white blood cells (WBCs) to the recipient. It helps to reduce undesirable side effects caused by co-existing blood components.

The spearation of individual blood components is done with a specialized centrifuge (see apheresis). The earliest manual forms of plateletpheresis are done by the separation of platelets from multiple bags of whole blood collected from donors or blood sellers. Since each blood bag (usually about 250 ml or 500 ml) only contains a small amount of platelets, it can take as many as a dozen blood bags (usually from 5 to 10 bags, depending on the size of blood bags and each donor's platelet count) to accumulate a single dose of platelets for just one patient. This greatly increased the risks of blood transfusion. Each unit of platelets separated from donated whole blood is called a "platelet concentrate".

Modern automatic plateletpheresis allows the blood donor to give a portion of his platelets, while keeping his red blood cells (RBCs) and at least a portion of blood plasma. Therefore, one or two doses of platelets can be safely harvested from each blood donor. This helps to further reduce undesirable side effects.

Requirements

• Weight
• Age
• RBC count
• WBC count
• Platelet count
• Fatty acids
• Interval

Other collected components

Even though RBCs can also be collected in the process, most blood donation organizations do not do so because it takes much longer for the human body to replenish the loss RBCs. If the donor donates both RBCs and platelets, it will take months rather than days or a couple of weeks for him/her to donate again (the guidelines regarding blood donation intervals are country-specific). This is surely a bad business strategy for the blood donation organizations.

Depending on the medical requirements, blood plasma is usually returned to the donor as well. However, in countries that have plasma processing facilities, a part of the donor's plasma can also be collected in a separate blood bag (see plasmapheresis).

Leukoreduction

Due to their higher relative density, WBCs are collected as an unwanted component with the platelets. Since it takes up to 3 liters of whole blood (the amount of a dozen of blood bags) to generate a dose of platelets, WBCs from one or several donors will also be collected alongside with platelets. A man of 70 kg has only about 6 liters of blood. If all WBCs go into the platelet blood bag, with so much foreign WBCs entering the body, it will surely cause damages. Therefore, it is a good idea to filter WBCs before transfusion of platelets. This is called leukoreduction, the reduction of leukocytes (WBCs).

Earlier platelet transfusions used a filter to remove WBCs at the time of transfusion. It takes a trained personnel about 10 minutes to assemble the equipments to filter the WBCs at bed-side. This is not the safest and most efficient way of filtration because living WBCs can release cytokines during storage and dead WBCs can break up into much smaller pieces of fragments that are causing immuno reactions. Moreover, bed-side filtration can lead to increased risks of infection and loss of valuable platelets. Many newer and more advanced plateletpheresis machines can filter WBCs at the time of separation.

For example, with marginally acceptible whole blood (WBCs: < 10,000/mm³; platelets: > 150,000/mm³), a dose (3×10¹¹) of platelets comes with about 2×10¹⁰ WBCs. This can seriously damage the patient's health. In comparison, a dose of platelets consist of multiple units of platelet concentrates may contain up to 6×10⁸ WBCs. A dose of single-donor platelets prepared using latest filters can only contain as little as 5×10^4~6 WBCs.

Manual platelet apheresis

• Platelet-rich plasma (PRP)
  • Widely used in North America
• Buffy coat (BC)
  • Widely used in Europe

Automatic platelet apheresis

The basic principles of automatic platelet apheresis are similar to the manual procedure. Only the whole procedure is done in a machine monitored by computer. Since the donor's blood is contained in a steriled single-use centrifuge, the processed blood can be returned to the donor's body safely. Therefore, the apheresis macine can repeat the draw-centrifuge-return cycle repeatedly to obtain more platelets.

A platelet donor usually must weight at least 50 kg (110 lb) and has a platelet count of at least 150×10⁵/mm³. Each country may have its detailed rules to protect the safety of both donor and recipient. A dose of platelet has about 3×10¹¹ platelets. Therefore, it takes 2 liters of blood having a platelet count of 150×10⁵/mm³ to produce one dose of platelets. Some regular donors have higher platelet counts (over 250-300×10⁵/mm³), it takes about one liter of their blood to produce a dose.

The blood takes about 8% of body weight. A 50 kg donor has about four liters of blood. The loss of platelets is never more than 50% and can be replenished by the body in about three days.

Most newer apheresis machines can separate a dose of platelets in about 60 to 120 minutes depending on the donor's health condition . Some models can even collect two doses in about the same time.

Haemonetics

The Haemonetics machine draws a larger amounts of blood in each cycle.

Usually 5-7 cycles (draw: 15 min, return: 10 min).

Trima

The Trima Automated Blood Collection System can collect two doses within two hours. The donor should have a platelet count of over 250×10⁵/mm³.

Trima draws and returns blood in very small amounts more frequently than Haemonetic's.

Usually more than 100 cycles (draw 40 sec, return 15 sec).