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What causes thrombocytopenia?
Low platelet counts, thrombocytopenia, can be caused by a variety of reasons. In general, they can be divided into:
decreased platelet production,
increased platelet destruction or consumption, or
increased splenic sequestration (capturing of circulating platelets in the spleen).
Some of the most common and important causes or thrombocytopenia are outlined below.
Decreased platelet production
Decreased platelet production is usually related to a bone marrow problem. In
some of these conditions, red blood cell and white blood cell productions may also be affected.
Viral infections affecting the marrow for example:
Epstein-Barr virus, and
Aplastic anemia is a general term used when the bone marrow fails to produce any blood cells (red cells, white cells, and platelets), also called pancytopenia. This can be caused by some viral infections (parvovirus or HIV), medications (gold, chloramphenicol, Dilantin, valproate (Depakote), or radiation, or rarely, it can be congenital (Fanconi's anemia).
Chemotherapy drugs frequently cause bone marrow suppression resulting in thrombocytopenia.
Some drugs other than chemotherapy can suppress platelet production, such as thiazide diuretics.
Cancers of the bone marrow and blood (leukemia) or cancers of the lymph nodes (lymphoma) can cause various degrees of thrombocytopenia.
Cancers from other organs can sometimes infiltrate (invade) the bone marrow and result in impaired production of platelets.
Long term alcohol can cause direct toxicity of the bone marrow.
Deficiency of vitamin B12 and folic acid can result in low platelet production by the bone marrow.
Increased platelet destruction or consumption
Increased platelet destruction or consumption can be seen a number of medical conditions. They can be divided into immune related and non-immune related causes.
Many medications can cause low platelet count by causing immunologic reaction against platelets, called drug-induced thrombocytopenia. Some examples may include:
Heparin, a commonly used blood thinner, and similar medications [low
molecular weight heparins like enoxaparin
(Lovenox) can occasionally induce an immune response against platelets resulting in rapid destruction of platelets. This condition is termed heparin-induced thrombocytopenia or HIT.
Idiopathic thrombocytopenic purpura (ITP) is a condition where the immune system attacks platelets. In severe conditions, ITP can result in very low platelet counts. In adults, this is
often a chronic (long standing) condition, whereas, in children, it can be caused acutely after a viral infection. This is usually a diagnosis of exclusion, meaning other causes need to be ruled out.
Some rheumatologic condition, such as systemic lupus erythematosus (SLE) or other autoimmune conditions (connective tissue diseases), can cause platelet destruction.
Transfusion of blood products and organ transplantation can sometimes cause immunologic disturbances resulting in thrombocytopenia.
Thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS) are
related conditions that can cause non-immune consumptive thrombocytopenia resulting from some
infections, pregnancy, some metastatic cancers, or chemotherapy. Other manifestations of these conditions include kidney insufficiency, confusion, anemia (hemolytic), and fever.
Classic HUS is largely seen in children and is generally thought of as an aftermath of an infection with a certain strain of Escherichia coli bacteria (E. coli O157:H7) which causes infectious diarrhea.
HELLP syndrome (hemolysis, elevated liver tests, low platelets) is another non-immune thrombocytopenia that may occur during pregnancy and can include elevation of liver enzymes and anemia (specifically, hemolytic anemia or rupturing of red blood cells).
Disseminated intravascular coagulopathy (DIC) is a rare but severe condition that may be a complication of overwhelming infections, traumas, burns, or pregnancy.
Injury to or inflammation of blood vessels (vasculitis) and, sometimes, artificial heart valves can cause increased destruction of platelets.
Severe infections (sepsis) or trauma can sometimes cause consumptive thrombocytopenia (without DIC).
Splenic sequestration can also lead to low platelet counts as a result of enlargement
or change in function of the spleen for a variety of reasons. When the spleen enlarges, it can retain (sequester) more than the usual amount of platelets. Common causes of thrombocytopenia due to splenic enlargement may include advanced liver disease
with portal hypertension (cirrhosis, for example, from chronic hepatitis B or C) and blood cancers (leukemias or lymphomas).
Dilutional thrombocytopenia can result from severe bleeding and transfusion of several units transfused red blood cells in a short time.
Pseudothrombocytopenia (false thrombocytopenia) is a commonly encountered condition where the number of platelets seen on a complete blood count analysis (CBC) may falsely appear low because of the clumping of platelets together. This can lead to
an artificially reduced automated count. If this is suspected, the blood can be redrawn in a tube with a material that prevents clumping of platelets for repeat analysis.
A peripheral smear review will identify platelet clumping.
Thrombocytopenia can also be present at birth, called neonatal thrombocytopenia. Most of these cases can be caused by processes similar to above, although, they are occasionally related to rare genetic conditions.