|3D rendering of four inactivated and three activated platelets|
Thrombocythemia is a condition of high platelet (thrombocyte) count in the blood. Normal count is in the range of 150x109 to 450x109 platelets per liter of blood,but investigation is typically only considered if the upper limit exceeds 750x109/L.
When the cause is unknown, the term thrombocythemia is used, as either primary thrombocythemia or essential thrombocythemia. The condition arises from a fault in the bone marrow cells leading to over-production of platelets but the cause of the fault is unknown, and this type is not common.
When the cause is known such as another disorder or disease, the term thrombocytosis is preferred, as either secondary or reactive thrombocytosis. Reactive thrombocytosis is the most common type and though it can often have no symptoms it can sometimes predispose to thrombosis. In contrast, thrombocytopenia refers to abnormally low blood platelet numbers in the blood.
High platelet counts do not necessarily signal any clinical problems, and can be picked up on a routine full blood count. However, it is important that a full medical history be elicited to ensure that the increased platelet count is not due to a secondary process. Often, it occurs in tandem with an inflammatory disease as the principal stimulants of platelet production (e.g. thrombopoietin) are elevated in these clinical states as part of the acute phase reaction. High platelet counts can occur in patients with polycythemia vera (high red blood cell counts), and is an additional risk factor for complications.[ citation needed ]
A very small number of people report symptoms of erythromelalgia, a burning sensation and redness of the extremities that resolves with cooling, or aspirin or both.
Scientific literature sometimes excludes thrombocytosis from the scope of thrombophilia by definition,but practically, by the definition of thrombophilia as an increased predisposition to thrombosis, thrombocytosis (especially primary thrombocytosis) is a potential cause of thrombophilia. Conversely, secondary thrombocytosis very rarely causes thrombotic complications.
Reactive thrombocythemia is the most common cause of a high platelet count. It accounts for 88% to 97% of thrombocythemia cases in adults, and near 100% in children. In adults, acute infection, tissue damage, chronic inflammation and malignancy are the common causes of reactive thrombocythemia. Usually, one or more of these conditions is present in more than 75% of the cases with reactive thrombocythemia. Causes for reactive thrombocytopenia in children are similar to adults. In addition, hemolytic anemia and thalassemia are often present in children living in the Middle East. Other causes of reactive thrombocythemia include: post surgery, iron deficiency, drugs, and rebound effect after bone marrow suppression.
The SARS disease caused thrombocytosis.
Once the reactive causes of thrombocythemia are ruled out, clonal thrombocythemia should be considered. The most common cause of clonal thrombocythemia is a myeloproliferative neoplasm. These include: essential thrombocythemia, chronic myelogenous leukemia, polycythemia vera, and primary myelofibrosis.
Extremely rare causes of thrombocythemia are spurious causes. This is due to the presence of structures resembling platelets in the blood such as needle-like cryoglobulin crystals, cytoplasmic fragments of circulating leukemic cells, bacteria, and red blood cell microvesicles. These structures are counted as platelets by the automated machine counter; therefore, causing the platelet number to be falsely elevated. However, such error can be avoided by doing a peripheral blood smear.
Laboratory tests might include: full blood count, liver enzymes, renal function and erythrocyte sedimentation rate.[ citation needed ]
If the cause for the high platelet count remains unclear, bone marrow biopsy is often undertaken, to differentiate whether the high platelet count is reactive or essential.[ citation needed ]
Often, no treatment is required or necessary for reactive thrombocytosis. In cases of reactive thrombocytosis of more than 1,000x109/L, it may be considered to administer daily low dose aspirin (such as 65 mg) to minimize the risk of stroke or thrombosis.
However, in essential thrombocythemia where platelet counts are over 750x109/L or 1,000x109/L, especially if there are other risk factors for thrombosis, treatment may be needed. Selective use of aspirin at low doses is thought to be protective. Extremely high platelet counts can be treated with hydroxyurea (a cytoreducing agent) or anagrelide (Agrylin).
In Janus kinase 2 positive disorders, ruxolitinib (Jakafi) can be effective.[ citation needed ]
Thrombosis is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel is injured, the body uses platelets (thrombocytes) and fibrin to form a blood clot to prevent blood loss. Even when a blood vessel is not injured, blood clots may form in the body under certain conditions. A clot, or a piece of the clot, that breaks free and begins to travel around the body is known as an embolus.
A thrombus, colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of cross-linked fibrin protein. The substance making up a thrombus is sometimes called cruor. A thrombus is a healthy response to injury intended to prevent bleeding, but can be harmful in thrombosis, when clots obstruct blood flow through healthy blood vessels.
Platelets, also called thrombocytes, are a component of blood whose function is to react to bleeding from blood vessel injury by clumping, thereby initiating a blood clot. Platelets have no cell nucleus; they are fragments of cytoplasm that are derived from the megakaryocytes of the bone marrow, which then enter the circulation. Circulating unactivated platelets are biconvex discoid (lens-shaped) structures, 2–3 µm in greatest diameter. Activated platelets have cell membrane projections covering their surface. Platelets are found only in mammals, whereas in other vertebrates, thrombocytes circulate as intact mononuclear cells.
Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism of coagulation involves activation, adhesion and aggregation of platelets, as well as deposition and maturation of fibrin.
Disseminated intravascular coagulation (DIC) is a condition in which blood clots form throughout the body, blocking small blood vessels. Symptoms may include chest pain, shortness of breath, leg pain, problems speaking, or problems moving parts of the body. As clotting factors and platelets are used up, bleeding may occur. This may include blood in the urine, blood in the stool, or bleeding into the skin. Complications may include organ failure.
Polycythemia vera is an uncommon myeloproliferative neoplasm in which the bone marrow makes too many red blood cells. It may also result in the overproduction of white blood cells and platelets.
Thrombocytopenia is a condition characterized by abnormally low levels of platelets, also known as thrombocytes, in the blood.
A megakaryocyte is a large bone marrow cell with a lobated nucleus responsible for the production of blood thrombocytes (platelets), which are necessary for normal blood clotting. In humans, megakaryocytes usually account for 1 out of 10,000 bone marrow cells, but can increase in number nearly 10-fold during the course of certain diseases. Owing to variations in combining forms and spelling, synonyms include megalokaryocyte and megacaryocyte.
Coronary thrombosis is defined as the formation of a blood clot inside a blood vessel of the heart. This blood clot may then restrict blood flow within the heart, leading to heart tissue damage, or a myocardial infarction, also known as a heart attack.
Hydroxycarbamide, also known as hydroxyurea, is a medication used in sickle-cell disease, chronic myelogenous leukemia, cervical cancer, and essential thrombocythemia. In sickle-cell disease it increases fetal hemoglobin and decreases the number of attacks. It is taken by mouth.
Essential thrombocythemia (ET) is a rare chronic blood cancer characterised by the overproduction of platelets (thrombocytes) by megakaryocytes in the bone marrow. It may, albeit rarely, develop into acute myeloid leukemia or myelofibrosis. It is one of four myeloproliferative neoplasms that occur when the body makes too many white or red blood cells, or platelets).
Heparin-induced thrombocytopenia (HIT) is the development of thrombocytopenia, due to the administration of various forms of heparin, an anticoagulant. HIT predisposes to thrombosis because platelets release microparticles that activate thrombin, thereby leading to thrombosis. When thrombosis is identified the condition is called heparin-induced thrombocytopenia and thrombosis (HITT). HIT is caused by the formation of abnormal antibodies that activate platelets. If someone receiving heparin develops new or worsening thrombosis, or if the platelet count falls, HIT can be confirmed with specific blood tests.
Thrombophilia is an abnormality of blood coagulation that increases the risk of thrombosis. Such abnormalities can be identified in 50% of people who have an episode of thrombosis that was not provoked by other causes. A significant proportion of the population has a detectable thrombophilic abnormality, but most of these develop thrombosis only in the presence of an additional risk factor.
Primary myelofibrosis (PMF) is a rare bone marrow blood cancer. It is classified by the World Health Organization (WHO) as a type of myeloproliferative neoplasm, a group of cancers in which there is abnormal growth of cells in the bone marrow. This overproduction is most often associated with a somatic mutation in the JAK2, CALR, or MPL gene markers. In PMF, the healthy marrow is replaced by scar tissue (fibrosis), resulting in a lack of production of normal blood cells. Symptoms include anemia, increased infection and an enlarged spleen (splenomegaly).
Myeloproliferative neoplasms (MPNs) are a group of rare blood cancers in which excess red blood cells, white blood cells or platelets are produced in the bone marrow. Myelo refers to the bone marrow, proliferative describes the rapid growth of blood cells and neoplasm describes that growth as abnormal and uncontrolled.
Anagrelide is a drug used for the treatment of essential thrombocytosis, or overproduction of blood platelets. It also has been used in the treatment of chronic myeloid leukemia.
Platelet transfusion, also known as platelet concentrate, is used to prevent or treat bleeding in people with either a low platelet count or poor platelet function. Often this occurs in people receiving cancer chemotherapy. Preventive transfusion is often done in those with platelet levels of less than 10 x 109/L. In those who are bleeding transfusion is usually carried out at less than 50 x 109/L. Blood group matching (ABO, RhD) is typically recommended before platelets are given. Unmatched platelets, however, are often used due to the unavailability of matched platelets. They are given by injection into a vein.
Basophilia is the condition of having greater than 200 basophils/μL in the venous blood.
Ruxolitinib, sold under the brand names Jakafi and Jakavi, is a medication for the treatment of intermediate or high-risk myelofibrosis, a type of myeloproliferative disorder that affects the bone marrow, polycythemia vera (PCV) when there has been an inadequate response to or intolerance of hydroxyurea, and steroid-refractory acute graft-versus-host disease. It was developed and marketed by Incyte Corp in the US under the brand name Jakafi, and by Novartis elsewhere in the world, under the brand name Jakavi.
Prefibrotic primary myelofibrosis (Pre-PMF) is a rare blood cancer, classified by the World Health Organization as a distinct type of myeloproliferative neoplasm in 2016. The disease is progressive to overt primary myelofibrosis, though the rate of progression is variable and not all patients progress. Symptoms and presentation can mimic essential thrombocythemia, with the main differentiator for pre-PMF being the presence of fibrosis in the bone marrow.