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Thrombocythemia is a condition of high
platelet
Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby ini ...
(thrombocyte) count in the blood. Normal count is in the range of 150x10
9 to 450x10
9 platelets per liter of blood,
but investigation is typically only considered if the upper limit exceeds 750x10
9/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
Bone marrow is a semi-solid tissue found within the spongy (also known as cancellous) portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production (or haematopoiesis). It is composed of hematopoietic ce ...
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
Thrombocytopenia is a condition characterized by abnormally low levels of platelets, also known as thrombocytes, in the blood. It is the most common coagulation disorder among intensive care patients and is seen in a fifth of medical patients an ...
refers to abnormally low blood platelet numbers in the blood.
Signs and symptoms
High platelet counts do not necessarily signal any clinical problems, and can be picked up on a routine
full blood count
A complete blood count (CBC), also known as a full blood count (FBC), is a set of medical laboratory tests that provide information about the cells in a person's blood. The CBC indicates the counts of white blood cells, red blood cells and plat ...
. 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
Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molecu ...
as the principal stimulants of platelet production (e.g.
thrombopoietin
Thrombopoietin (THPO) also known as megakaryocyte growth and development factor (MGDF) is a protein that in humans is encoded by the ''THPO'' gene.
Thrombopoietin is a glycoprotein hormone produced by the liver and kidney which regulates the pro ...
) are elevated in these clinical states as part of the
acute phase reaction
Acute-phase proteins (APPs) are a class of proteins whose concentrations in blood plasma either increase (positive acute-phase proteins) or decrease (negative acute-phase proteins) in response to inflammation. This response is called the ''acute-p ...
. High platelet counts can occur in patients with
polycythemia vera
Polycythemia vera is an uncommon myeloproliferative neoplasm (a type of chronic leukemia) in which the bone marrow makes too many red blood cells. It may also result in the overproduction of white blood cells and platelets.
Most of the health ...
(high
red blood cell
Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...
counts), and is an additional risk factor for complications.
A very small number of people report symptoms of
erythromelalgia
Erythromelalgia or Mitchell's disease (after Silas Weir Mitchell) is a rare vascular peripheral pain disorder in which blood vessels, usually in the lower extremities or hands, are episodically blocked (frequently on and off daily), then become ...
, a burning sensation and redness of the extremities that resolves with cooling, or
aspirin
Aspirin, also known as acetylsalicylic acid (ASA), is a nonsteroidal anti-inflammatory drug (NSAID) used to reduce pain, fever, and/or inflammation, and as an antithrombotic. Specific inflammatory conditions which aspirin is used to treat inc ...
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
Essential thrombocythemia (ET) is a rare chronic blood cancer (myeloproliferative neoplasm) characterised by the overproduction of platelets (thrombocytes) by megakaryocytes in the bone marrow. It may, albeit rarely, develop into acute myeloid le ...
) is a potential cause of thrombophilia. Conversely,
secondary thrombocytosis
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. ...
very rarely causes thrombotic complications.
Causes
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
Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irritation, irritants, and is a protective response involving im ...
and
malignancy
Malignancy () is the tendency of a medical condition to become progressively worse.
Malignancy is most familiar as a characterization of cancer. A ''malignant'' tumor contrasts with a non-cancerous ''benign'' tumor in that a malignancy is not s ...
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 thrombocythemia in children are similar to adults. In addition,
hemolytic anemia
Hemolytic anemia or haemolytic anaemia is a form of anemia due to hemolysis, the abnormal breakdown of red blood cells (RBCs), either in the blood vessels (intravascular hemolysis) or elsewhere in the human body (extravascular). This most commonly ...
and
thalassemia
Thalassemias are inherited blood disorders characterized by decreased hemoglobin production. Symptoms depend on the type and can vary from none to severe. Often there is mild to severe anemia (low red blood cells or hemoglobin). Anemia can result ...
are often present in children living in the
Middle East
The Middle East ( ar, الشرق الأوسط, ISO 233: ) is a geopolitical region commonly encompassing Arabian Peninsula, Arabia (including the Arabian Peninsula and Bahrain), Anatolia, Asia Minor (Asian part of Turkey except Hatay Pro ...
. Other causes of reactive thrombocythemia include: post
surgery
Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical specialty that uses operative manual and instrumental techniques on a person to investigate or treat a pat ...
,
iron deficiency
Iron deficiency, or sideropenia, is the state in which a body lacks enough iron to supply its needs. Iron is present in all cells in the human body and has several vital functions, such as carrying oxygen to the tissues from the lungs as a key ...
, drugs, and
rebound effect
The rebound effect, or rebound phenomenon, is the emergence or re-emergence of symptoms that were either absent or controlled while taking a medication, but appear when that same medication is discontinued, or reduced in dosage. In the case of re ...
after
bone marrow suppression
Bone marrow suppression also known as myelotoxicity or myelosuppression, is the decrease in production of cells responsible for providing immunity ( leukocytes), carrying oxygen ( erythrocytes), and/or those responsible for normal blood clotting ...
.
The
SARS
Severe acute respiratory syndrome (SARS) is a viral respiratory disease of zoonotic origin caused by the severe acute respiratory syndrome coronavirus (SARS-CoV or SARS-CoV-1), the first identified strain of the SARS coronavirus species, ''sever ...
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
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 growt ...
. These include:
essential thrombocythemia
Essential thrombocythemia (ET) is a rare chronic blood cancer (myeloproliferative neoplasm) characterised by the overproduction of platelets (thrombocytes) by megakaryocytes in the bone marrow. It may, albeit rarely, develop into acute myeloid leuk ...
,
chronic myelogenous leukemia
Chronic myelogenous leukemia (CML), also known as chronic myeloid leukemia, is a cancer of the white blood cells. It is a form of leukemia characterized by the increased and unregulated growth of myeloid cells in the bone marrow and the accumulat ...
,
polycythemia vera
Polycythemia vera is an uncommon myeloproliferative neoplasm (a type of chronic leukemia) in which the bone marrow makes too many red blood cells. It may also result in the overproduction of white blood cells and platelets.
Most of the health ...
, and
primary myelofibrosis
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 growth of abnormal cells in the bone marrow. T ...
.
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
A blood smear, peripheral blood smear or blood film is a thin layer of blood smeared on a glass microscope slide and then stained in such a way as to allow the various blood cells to be examined microscopically. Blood smears are examined in the ...
.
Diagnosis
Laboratory tests might include:
full blood count
A complete blood count (CBC), also known as a full blood count (FBC), is a set of medical laboratory tests that provide information about the cells in a person's blood. The CBC indicates the counts of white blood cells, red blood cells and plat ...
,
liver enzyme
Liver function tests (LFTs or LFs), also referred to as a hepatic panel, are groups of blood tests that provide information about the state of a patient's liver. These tests include prothrombin time (PT/INR), activated partial thromboplastin tim ...
s,
renal function
Assessment of kidney function occurs in different ways, using the presence of symptoms and signs, as well as measurements using urine tests, blood tests, and medical imaging.
Functions of a healthy kidney include maintaining a person's fluid ...
and
erythrocyte sedimentation rate
The erythrocyte sedimentation rate (ESR or sed rate) is the rate at which red blood cells in anticoagulated whole blood descend in a standardized tube over a period of one hour. It is a common hematology test, and is a non-specific measure of ...
.
If the cause for the high platelet count remains unclear,
bone marrow
Bone marrow is a semi-solid tissue found within the spongy (also known as cancellous) portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production (or haematopoiesis). It is composed of hematopoietic ce ...
biopsy
A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, or an interventional cardiologist. The process involves extraction of sample cells or tissues for examination to determine the presence or extent of a diseas ...
is often undertaken, to differentiate whether the high platelet count is reactive or essential.
Treatment
Often, no treatment is required or necessary for reactive thrombocytosis. In cases of reactive thrombocytosis of more than 1,000x10
9/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 750x10
9/L or 1,000x10
9/L, especially if there are other risk factors for thrombosis, treatment may be needed. Selective use of
aspirin
Aspirin, also known as acetylsalicylic acid (ASA), is a nonsteroidal anti-inflammatory drug (NSAID) used to reduce pain, fever, and/or inflammation, and as an antithrombotic. Specific inflammatory conditions which aspirin is used to treat inc ...
at low doses is thought to be protective. Extremely high platelet counts can be treated with
hydroxyurea
Hydroxycarbamide, also known as hydroxyurea, is a medication used in sickle-cell disease, essential thrombocythemia, chronic myelogenous leukemia, polycythemia vera, and cervical cancer. In sickle-cell disease it increases fetal hemoglobin and d ...
(a cytoreducing agent) or
anagrelide
Anagrelide (Agrylin/Xagrid, Shire and Thromboreductin, AOP Orphan Pharmaceuticals AG) is a drug used for the treatment of essential thrombocytosis (also known as essential thrombocythemia), or overproduction of blood platelets. It also has been u ...
(Agrylin).
In
Janus kinase 2
Janus kinase 2 (commonly called JAK2) is a non-receptor tyrosine kinase. It is a member of the Janus kinase family and has been implicated in signaling by members of the type II cytokine receptor family (e.g. interferon receptors), the GM-CSF re ...
positive disorders,
ruxolitinib
Ruxolitinib, sold under the brand names Jakafi and Jakavi, is a medication used for the treatment of intermediate or high-risk myelofibrosis, a type of myeloproliferative disorder that affects the bone marrow; polycythemia vera (PCV), when ther ...
(Jakafi) can be effective.
References
Further reading
*
External links
{{Diseases of megakaryocytes, us=y, state=collapsed
Coagulopathies