Overview of Platelet Disorders

Platelets (sometimes called thrombocytes) are cell fragments produced in the bone marrow 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 material inside their cell body (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 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

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.