• Also Known As:
  • Thrombocytopenia
  • Immune Thrombocytopenia (ITP)
  • Immune Thrombocytopenic Purpura
  • Idiopathic Thrombocytopenic Purpura
  • Heparin-induced Thrombocytopenia (HIT)
  • Thrombotic Thrombocytopenic Purpura (TTP)
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What are platelets?

Platelets (thrombocytes) are tiny fragments of very large cells called megakaryocytes in the bone marrow. Platelets are released into the blood to circulate and are essential for proper blood clotting.

When there is an injury to a blood vessel or to tissue and bleeding begins, platelets help stop bleeding in multiple ways. They:

  • Adhere to the injury site
  • Clump together (aggregate) with other platelets to form a temporary plug
  • Release chemical signals that stimulate further aggregation of other platelets
  • Support the coagulation cascade, a process in which clotting factors in the blood are sequentially activated to help form a blood clot (thrombus)
  • Eventually become part of a stable blood clot at the site of the injury that remains in place until the injury heals

There are normally about 150,000 to 450,000 platelets per microliter of blood. For reference, a drop of liquid is about 50 microliters. So, a healthy person will have millions of platelets in a single drop of blood. Because of many small injuries that occur regularly, platelets are constantly being used up. They have a life span of about 8 to 10 days. Thus, the bone marrow must continually produce new platelets to replace those that are degraded, used up, and lost through bleeding.

The number of platelets in your blood can be determined with a platelet count, a common test that is usually done as part of a complete blood count (CBC). You may have a CBC done as part of a routine health exam or when your healthcare practitioner is evaluating you for a particular condition.

Your platelet count is interpreted by your healthcare practitioner within the context of other tests that you have had done (e.g., CBC) as well as other factors, such as your medical history. If you have a low platelet count, it means you have too few platelets circulating in your blood. Your blood may not clot appropriately and you may be at an increased risk for easy bruising and/or excessive bleeding.

However, a single low platelet count may or may not have medical significance. Generally, this is the case when the result is only slightly lower than the reference (normal) range. Your healthcare practitioner may repeat the test and may look at results from prior platelet counts. On the other hand, a result outside the reference range may indicate a problem and warrant further investigation. Your healthcare practitioner will determine whether a result that falls outside of the reference range means something significant for you.

A low platelet count, also called thrombocytopenia, can be caused by various conditions. It may develop suddenly (acute), may be temporary, or persist over time (chronic).

The risk for serious bleeding with thrombocytopenia does not happen until the number of platelets is very low, around 20,000 per microliter or lower. However, minor bleeding can be seen at about 50,000 per microliter if another condition is present (e.g., kidney disease). The number of platelets can drop rapidly depending on the condition that is causing the low number of platelets.

If your platelets are severely low and you are at risk of bleeding, you may be treated to increase your platelets and to reduce bleeding risk. After that, testing may be done to help determine a cause.


About Low Platelets

Causes of low platelet counts

A number of conditions and factors can cause a low platelet count. They can be rare inherited (genetic) conditions or they can be conditions that develop later in your life (acquired). Occasionally, an enlarged spleen due to a variety of conditions, can trap platelets and lead to low platelet counts.

Generally, a low platelet count can come from one of two mechanisms:

Decreased Platelet Production
Anything that interferes with platelet production by the bone marrow can cause low platelets. Some examples include:

  • Cancers—some cancers such as leukemia, lymphoma, or another cancer that has spread to the bone marrow can cause a low platelet count. The cancer cells in the bone marrow may crowd out the normal bone marrow cells, including the cells that form platelets (megakaryocytes). People with leukemia often experience excessive bleeding due to a significantly decreased number of platelets.
  • Aplastic anemia—with this condition, the bone marrow’s production of all blood cell types is significantly decreased because the bone marrow is failing.
  • Chemotherapy or radiation therapy—can affect the bone marrow’s ability to produce platelets
  • Myelodysplastic syndrome—a group of disorders associated with dysfunctional and ineffective bone marrow that leads to decreased production of one or more types of blood cells
  • Vitamin B12 and folate deficiency—over time, a deficiency in either B12 or folate can lead to fewer but enlarged red blood cells (macrocytic anemia) as well as low platelets.
  • Bone marrow infection—infections can spread through the blood to the bone or an injury to bone can become infected. Most bone infections are caused by staphylococcus bacteria.
  • Bone marrow damage—caused by exposure to toxic chemicals such as benzene or certain pesticides
  • Cirrhosis—besides causing decreased platelet production, there are other factors that can contribute to low platelets in cirrhosis.

Some examples of rare inherited conditions that affect platelet production include:

  • Wiskott-Aldrich syndrome—a decrease in the size and number of platelets. This condition primarily affects males.
  • May-Hegglin anomaly—causes giant misshapen platelets and may result in low numbers of platelets
  • Gaucher disease—fatty substances accumulating in the spleen (and liver) can cause them to enlarge, reducing the number of circulating platelets.

Increased Platelet Use or Destruction
Some conditions or factors can cause platelets to be used up or destroyed faster than the bone marrow can produce them. Although these can increase risk of low platelets, many people with these conditions or factors have normal platelet counts and function.

Some examples include:

  • Viral infections such as mononucleosis, hepatitis, HIV, or measles
  • Sepsis, especially sepsis resulting from a serious Gram-negative bacterial infection (e.g., Escherichia coli, E. coli)
  • Certain drugs can cause low platelets. A few examples include acetaminophen, quinine, sulfa antibiotics, digoxin, vancomycin, diazepam, nitroglycerin, gold salts, and some diuretics.
  • Pregnancy—platelet counts tend to drop during pregnancy though remain within the reference range. Gestational thrombocytopenia (platelet count between 100,000 and 150,000) may occur in about 10% of pregnant women. Platelet counts less than 100,000 can be potentially life-threatening and can occur in immune thrombocytopenia, pre-eclampsia, or HELLP syndrome (hemolysis, elevated liver enzymes, low platelets).
  • Dilution—massive blood (red blood cells) transfusion without giving platelets (thrombocytopenia due to dilution effect)
  • Physical destruction of platelets, for example caused by artificial heart valves or equipment used during heart bypass surgeries
  • Disseminated intravascular coagulation (DIC)—this is a devastating and severe response that may occur due to system-wide infection, burns, or severe trauma, causing a significant and rapid decrease in platelet numbers.
  • Hemolytic uremic syndrome (HUS)—usually a result from a severe toxin-producing E. coli infection of the gut, causing destruction of platelets and red blood cells
  • Thrombotic thrombocytopenic purpura (TTP) is an acute, potentially life-threatening, though rare condition. It causes both clotting and destruction of red blood cells. Tiny clots form and deposit in small blood vessels throughout the body. This clotting uses up platelets at an accelerated rate, leading to a low number of platelets. It may be due to an inherited predisposition (rare) or it can be acquired.
  • Immune-related conditions that increase destruction of platelets—the body’s natural defense system, the immune system, normally protects against infections. It is usually able to distinguish between “self” and “non-self.” With autoimmune conditions, the body mistakenly recognizes its own proteins and tissues as “non-self” and produces an immune response of antibodies that target them. Your body can develop antibodies against platelets, thus greatly reducing their numbers. Some examples of immune-related diseases that can result in low platelets include:
    1. Immune thrombocytopenia (ITP, also called immune thrombocytopenic purpura or “idiopathic” thrombocytopenic purpura) is the most common cause of low platelets in children. In children, it typically develops after a viral infection and then resolves fully within a few months, often without treatment. Boys and girls are equally affected. With adults, ITP is more likely to be a chronic condition, affecting more women than men.
    2. Immune response when you already have an existing autoimmune condition such as lupus or rheumatoid arthritis
    3. Heparin-induced thrombocytopenia (HIT) results in low platelets when you are on (or recently have been on) heparin therapy and develop a platelet antibody. HIT is often associated with abnormal clotting rather than bleeding. (For more on this, see the article on HIT Antibody).
    4. Fetal or neonatal alloimmune thrombocytopenia (NAIT)—this is a rare immune-related condition but is a common cause of low platelets in newborns. It occurs when a pregnant mother develops antibodies against the developing baby’s platelets and recognizes them as “non-self.” The mother’s antibodies attack and destroy the fetus’ platelets. Most cases are mild, but serious cases can cause bleeding episodes and may require treatment.

Signs and Symptoms

Depending on how low your platelets are, you may have no noticeable signs or symptoms. In this case, the low platelets may be found by chance, such as during routine testing for a health exam.

If your platelet count is significantly low, however, you may develop signs and symptoms. Some examples include:

  • Unexplained, easy bruising
  • Small red spots on the skin that may sometimes look like a rash (petechiae)
  • Small purplish spots caused by bleeding under your skin (purpura)
  • Prolonged bleeding from a small cut or wound
  • Frequent nosebleeds
  • Bleeding in the digestive tract (black stools may be present)
  • Heavy menstrual bleeding
  • Bleeding from your mouth and gums
  • Bleeding inside your head (intracranial)


Low platelets (thrombocytopenia) can be diagnosed, evaluated, and monitored through blood tests. There is no single test to identify the underlying cause, but several tests may be done to determine why your platelets are low and to guide your treatment.

Laboratory Tests
Routine tests may include one or more of the following:

Other, more specialized tests may also be done to help diagnose the underlying cause of low platelets and to identify any contributing factors. The tests performed depend on the suspected condition. Some examples include:

Non-Laboratory Tests
Some other evaluations and imaging tests may be done to help diagnose the cause of low platelets. Some examples include:

  • Clinical medical history, family history, and an evaluation of all medications, supplements, food, and alcohol consumption
  • Sometimes an ultrasound of the spleen is performed to see if it is enlarged.
  • Sometimes a computed tomography (CT) or magnetic resonance imaging (MRI) scan may be done if internal bleeding is suspected.


Treatment depends on your condition’s severity and its cause. The most important treatment in the short term is to address severely low platelets and bleeding. After that, the underlying cause for the thrombocytopenia may be identified and treated. If the cause cannot be identified (“idiopathic”), then your low platelets must be managed and monitored. In some cases, when the cause cannot be diagnosed, low platelets will resolve without specific treatment, while in other cases, the condition may persist and require long-term treatment.

Mild to moderate thrombocytopenia:

  • Treatment may not be required but you will be monitored over time until the low platelet condition is resolved.
  • If the cause of your thrombocytopenia is a drug, then your condition is likely to resolve when you stop taking the drug.
  • Treatment may be necessary depending on your health status, for example, if you require surgery and your low platelets are considered a risk for bleeding.

If your condition gets worse or is severe, treatment may be necessary. Possible treatments include:

  • Platelet transfusions—this may be done if your platelets are critically low. (For more details, read the article on Transfusion Medicine.)
  • Prednisone—a steroid that helps improve platelet counts by slowing destruction
  • IV immunoglobulin (IVIG)—may be given when you have an immune-related thrombocytopenia; alternatively, anti-D immunoglobulin (if you are Rh-positive) may be given.
  • A drug such as romiplostim can be given to promote platelet production.
  • Surgery to remove the spleen (splenectomy)—platelet antibodies attach to platelets, which are then destroyed by the spleen; removing your spleen can decrease platelet destruction and may be done if other treatments have not been successful.
  • Switching to a different anticoagulant when low platelets are related to heparin therapy (immune-mediated heparin-induced thrombocytopenia)

For more details on treatment, see the links in the Related Content section.

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