Platelets, also called blood thrombocytes, are among the cellular components of blood and play an important role in blood clotting and thus hemostasis. A low number of platelets in the blood results in an increased tendency to bleed, while an increased number increases the risk of clot formation in the vessels. The body’s platelet count can be determined by a simple blood test.
What are platelets?
A blood test is used by physicians to further diagnose various diseases. In addition to erythrocytes and leukocytes, platelets are a cellular component of blood. The flat, dented, seedless discs are formed in the bone marrow. Their name is derived from ancient Greek and means “vessel”/”cavity” according to the platelet shape. Platelets are formed by strangulation of so-called megakaryoblasts (also known as bone marrow giant cells). Each individual platelet divides into a bright outer region and a readily stainable center. This center of the platelet contains clotting factors and cell organelles (cell structures). After their average life span of about 10 days, they are degraded in the spleen and liver. Platelets represent the smallest cells in the human body. Their size is only about 1-4µm – therefore they are only visible under a light microscope.
Measure blood values, blood test and platelets.
In healthy adult women and men, about 150,000-350,000 platelets are found per µl of blood. Platelet counts are determined as part of a blood count – with the help of fully automated particle counters. This allows the physician to determine whether the platelet count is within the normal range. An examination is recommended, for example, if there are symptoms of an increased tendency to bleed, before operations, after large blood losses, or if there is a suspicion of the presence of a thrombus (blockage of the bloodstream). Based on the bleeding time (time from injury to cessation of bleeding), platelet function can be tested.
Function, action, and roles
After a vessel is injured, for example by a cut, platelets attach to the connective tissue fibers of the wound edges. This process is called platelet adhesion. The individual platelets deform and clump together – this is called platelet aggregation. This results in the formation of a plug. The formation of this “wound patch” aims to close the wound and thus reduce blood loss. By simultaneously releasing messenger substances, the platelets start blood coagulation – this leads to further stabilization of the hemostatic plug. If the platelets are impaired in their function or reduced in number, it takes much longer for the bleeding to stop in the event of an injury. In addition, platelets have an important function in the immune defense system. Through a process called endocytosis, (uptake of non-cellular material into the cell), they absorb foreign substances from the blood before they lead to the initiation of disease.
Diseases
A decrease in platelet count (below 150,000/µl) is called thrombocytopenia and is associated with an increased tendency to bleed. In the event of an injury, there is then prolonged or increased bleeding, due to delayed hemostasis. In mild cases, patients also complain of an increased incidence of bruising or frequent nosebleeds. Another characteristic feature is the occurrence of petechiae – pinpoint hemorrhages on the skin and mucous membranes. In severe cases (platelet concentration below 1,000/µl), severe, sometimes life-threatening bleeding may occur. The following factors can trigger thrombocytopenia: Leukemia, chemotherapy, infectious diseases such as malaria, ringworm or Helicobacter pylori, pregnancy, etc. The therapy of thrombocytopenia depends on the triggering cause. A life-threatening reduction of platelets can be compensated by the administration of platelet concentrates. On the other hand, an increased number of platelets in the blood (above 1,000,000/µl) is called thrombocytosis. In this context, the risk of clot formation resulting in vascular occlusion is increased. For example, in the presence of an infection, the body reacts with an increased production of platelets.Accordingly, an increase in platelets may possibly be an indication of inflammation. As a result of large blood losses (e.g., due to surgery) or heavy stress on the body (e.g., competitive sports), the body also reacts with thrombocytosis.
