A considerable portion of blood is contains platelets which are fragments of megakaryocytes, the cells in the bone marrow. After stimulation by a specific hormone known as thrombopoietin, the platelets come away from the megakaryocytes and enter the blood stream to circulate. On entering the blood stream they have about ten days to do their work before being filtered out by the spleen.
Through the hormones and proteins that they contain, platelets assist the blood to clot after a bruise or injury. Without them, you could bleed to death. However, an excess of platelets can lead blood clots in the blood stream which cause strokes. There are times when a lowered platelet level is required and can be induced by a daily dosage of aspirin and other drugs. Platelet counts are lowered for stroke patients, patients using intravenous drips and those who have had their heart repaired.
Burn victims, chemotherapy patients, marrow transplant patients and organ transplant patients often have very low platelet counts and require platelet transfusions. Platelets are acquired the same way as blood transfusions. The blood is drawn out into a centrifuge which separates the platelets other substances in the blood. The rest of the blood is then transfused back into the donor’s body. The procedure takes longer than then normal blood donation and can last up to about two hours. Platelets can only survive for about five days before they are transfused. For a full transfusion unit, at least six separate donations are required. A bone marrow transplant patient requires up to 120 platelets units which is 720 people donating platelets.