Platelet

Platelets, or thrombocytes are cells that stick together to form blood clots. They join together when exposed to the air (as in a cut or disturbance of blood vessel), though they are not cells in the conventional sense, but are fragmented pieces of megakaryocyte cytoplasm released from the bone marrow into the blood stream.

Platelets are separated, by centrifugation, from the rest of donated blood and given to patients who need them. A (see-through) bag of them is pale orange. They are separated because they don't survive the normal storage used for red blood cells, and must be stored separately.

A normal platelet count in a healthy person is between 150 and 400 (x 10⁹/L of blood). People can live independently with a count as low as 20. People can live in hospital with a count as low as 5, but spontaneous bleeding gets to be a problem. Platelets can be transfused if a patient's platelet count falls too low. A low platelet count is called thrombocytopenia, having too many platelets is called thrombocytosis.

See Also: Hemostasis