Platelets (sometimes called thrombocytes) are cell fragments that circulate in the bloodstream and help blood to clot How Blood Clots Hemostasis is the body's way of stopping injured blood vessels from bleeding. Hemostasis includes clotting of the blood. Too little clotting can cause excessive bleeding from minor injury Too... read more . Thrombopoietin, primarily produced in the liver, stimulates the bone marrow to make large cells (megakaryocytes), which in turn make platelets from their cytoplasm. Platelets that are not used in clots circulate for 7 to 10 days and are then destroyed. About one third are always stored in the spleen.
The platelet count (number of platelets circulating in the bloodstream) is usually about 140,000 to 440,000 platelets per microliter (140 × 109 to 440 × 109 per liter). The platelet count can vary according to the menstrual cycle. It can decrease near the end of pregnancy (gestational thrombocytopenia) and increase in response to inflammation (secondary, or reactive, thrombocytosis). Neither of these conditions is serious, and most affected people have no problems resulting from either one.
Platelet disorders include
An abnormal increase in platelets (essential thrombocythemia Essential Thrombocythemia Essential thrombocythemia is a myeloproliferative neoplasm in which excess platelets are produced, leading to abnormal blood clotting or bleeding. The hands and feet may burn, turn red, and... read more and reactive thrombocytosis Secondary Thrombocythemia Secondary thrombocythemia is excess platelets in the bloodstream that develops as a result of another disorder and rarely leads to excessive blood clotting or bleeding. Platelets (thrombocytes)... read more )
Any of these disorders can cause problems with blood clotting.
In essential thrombocythemia Essential Thrombocythemia Essential thrombocythemia is a myeloproliferative neoplasm in which excess platelets are produced, leading to abnormal blood clotting or bleeding. The hands and feet may burn, turn red, and... read more , the bone marrow cells that make platelets grow excessively and make too many platelets despite no other disorder being identified. Surprisingly, the increased number of platelets most often causes excessive bleeding rather than clotting. Doctors sometimes give people aspirin to lower the risk of abnormal clotting if they have vascular disease or are at increased risk of a heart attack. Drugs to lower the platelet count may sometimes be needed.
In reactive thrombocytosis Secondary Thrombocythemia Secondary thrombocythemia is excess platelets in the bloodstream that develops as a result of another disorder and rarely leads to excessive blood clotting or bleeding. Platelets (thrombocytes)... read more , another medical disorder stimulates the bone marrow to make too many platelets (the platelets are made in reaction to the other disorder). Such disorders include infections, chronic inflammation (such as occurs in rheumatoid arthritis Rheumatoid Arthritis (RA) Rheumatoid arthritis is an inflammatory arthritis in which joints, usually including those of the hands and feet, are inflamed, resulting in swelling, pain, and often destruction of joints.... read more and inflammatory bowel disease Overview of Inflammatory Bowel Disease (IBD) In inflammatory bowel diseases, the intestine (bowel) becomes inflamed, often causing recurring abdominal pain and diarrhea. The two primary types of inflammatory bowel disease (IBD) are Crohn... read more ), iron deficiency Iron Deficiency Iron deficiency is a common cause of anemia, a condition in which the number of red blood cells is low. Iron deficiency usually results from loss of blood in adults (including bleeding from... read more , and certain cancers. The increased numbers of platelets usually do not cause any increase in clotting or bleeding risk. Specific treatment is not needed for the high number of platelets, but the underlying condition may need to be treated.
In thrombocytopenia Overview of Thrombocytopenia Thrombocytopenia is a low number of platelets (thrombocytes) in the blood, which increases the risk of bleeding. Thrombocytopenia occurs when the bone marrow makes too few platelets or when... read more , there are many causes of decreased numbers of platelets. Causes are generally divided into those involving decreased production of platelets and those involving increased destruction or loss of platelets.
In platelet dysfunction Platelet Dysfunction Platelet dysfunction may be due to a problem in the platelets themselves or to an external factor that alters the function of normal platelets. (See also Overview of Platelet Disorders and Overview... read more , people have the correct number of platelets, but the platelets do not function normally.
Bleeding in the skin may be the first sign of a low platelet count or platelet dysfunction. Many tiny red dots (petechiae) often appear in the skin on the lower legs, and minor injuries (including needlesticks) may cause black-and-blue bruises (ecchymoses or purpura). The gums may bleed, and blood may appear in the stool or urine. Menstrual periods or nosebleeds may be unusually heavy. The lower the platelet count, the more severe the symptoms.
People with too many platelets may have the same signs of bleeding as people with too few platelets because a very high number of platelets can absorb enough of an important clotting factor Blood clotting factors Hemostasis is the body's way of stopping injured blood vessels from bleeding. Hemostasis includes clotting of the blood. Too little clotting can cause excessive bleeding from minor injury Too... read more (a protein found in blood that works with platelets to help the blood clot ) to cause bleeding. However, some people instead have symptoms caused by abnormal blood clots. For example, people may have a swollen leg from a blood clot in a vein in their leg Deep Vein Thrombosis (DVT) Deep vein thrombosis is the formation of blood clots (thrombi) in the deep veins, usually in the legs. Blood clots may form in veins if the vein is injured, a disorder causes the blood to clot... read more , or they may have numbness and weakness because of a blood clot in their brain causing a stroke Ischemic Stroke An ischemic stroke is death of an area of brain tissue (cerebral infarction) resulting from an inadequate supply of blood and oxygen to the brain due to blockage of an artery. Ischemic stroke... read more .
Doctors can diagnose many platelet disorders by a simple blood test (a complete blood count Complete blood count Doctors select tests to help diagnose blood disorders based on the person's symptoms and the results of the physical examination. Sometimes a blood disorder causes no symptoms but is discovered... read more [CBC]) to measure the number of platelets.
Special tests may be needed to diagnose platelet dysfunction.