Thrombocytopenia is the name for a low platelet count. Platelets are blood cells that help blood clot. The two main factors that cause low platelet counts are medication side effects and underlying health conditions.

A reduced platelet count in the blood is not always a serious problem. However, the condition affects the blood’s ability to clot. If a person’s blood does not clot, a wound may bleed severely. This can have serious complications in some cases.

This article examines the conditions, medications, and substances that can cause a low platelet count. It also outlines how to recognize the symptoms and what to expect from treatment.

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A platelet count measures the concentration of platelets in the blood. A normal platelet count is 150,000–450,000 platelets/µl. When the number of platelets is low, this concentration reduces.

A person with thrombocytopenia will have a platelet count below 150,000/µl.

Females usually experience a platelet count that varies slightly during the menstrual cycle and can fall near the end of pregnancy.

Thrombocytopenia may make it difficult for the body to stop bleeding following an injury. Bleeding can occur inside the body, beneath the skin, or at the skin’s surface.

People with thrombocytopenia usually do not experience serious bleeding until their platelet count is very low.

Learn more about platelet count ranges in thrombocytopenia.

Two main factors cause a person to have a low platelet count: an underlying health condition or a medication. These factors can lower the platelet count by affecting the production, storage, use, or destruction of platelets.

Medical conditions that can cause a low platelet count

A low platelet count may occur due to:

  • the bone marrow not producing enough platelets
  • the body destroying or using up the platelets that the bone marrow produces
  • the spleen holding onto too many platelets, meaning that the amount in the blood is too low

Certain medical conditions can also cause a person to have a low platelet count. These include:

  • Aplastic anemia: This rare blood condition occurs when the bone marrow stops making adequate new blood cells.
  • Autoimmune diseases: Certain autoimmune diseases can mistakenly cause a person’s immune system to attack and destroy their platelets. Diseases that can do this include idiopathic thrombocytopenic purpura (ITP), lupus, and rheumatoid arthritis.
  • Cancer: Some cancers, such as leukemia or lymphoma, can damage bone marrow and destroy blood stem cells. This can cause the stem cells to stop growing healthy blood cells. Some cancer treatments, including radiation therapy and chemotherapy, may also destroy stem cells.
  • Conditions that cause blood clots: Some conditions cause blood clots to develop. These conditions include thrombotic thrombocytopenic purpura (TTP) and disseminated intravascular coagulation (DIC). These conditions can cause the body to use all of the available platelets, leading to a low platelet count.
  • Infections: Bacterial or viral infections may temporarily lower a platelet count.
  • Large spleen: If a person’s spleen is large, it may store too many platelets. This can cause a low platelet count in the blood.
  • Surgery: In some cases, artificial heart valves, blood vessel grafts, or machines and tubing for blood transfusions or bypass surgery may destroy platelets.

Pregnancy can sometimes cause a person to develop mild thrombocytopenia. The exact reason for this is unknown, but it seems to be more common close to delivery.

Medications and substances that can cause a low platelet count

Various substances can cause a person to have a low platelet count, including:

  • medications
  • poisonous substances, such as pesticides, arsenic, and benzene
  • heavy alcohol consumption
  • quinine, which is in tonic water and some tablets for leg cramps

If a substance is causing a person’s low platelet count, a doctor may suggest that they stop taking it. Doing so should return the platelet count to normal.

If the cause is a drug a person takes for a different condition, the prescribing doctor might change the medication.

Over-the-counter (OTC) medications that can cause a low platelet count include:

Prescription medications that can cause thrombocytopenia include:

  • amiodarone
  • ampicillin and other antibiotics
  • cimetidine
  • glycoprotein IIb/IIIa inhibitors, including abciximab, eptifibatide, and tirofiban
  • heparin
  • piperacillin
  • seizure medications, such as carbamazepine
  • sulfonamides, such as trimethoprim-sulfamethoxazole
  • vancomycin

Symptoms of a low platelet count only occur at severely low levels. A count that is only slightly lower than normal may not produce symptoms.

If the count is low enough to cause spontaneous bleeding, an individual may notice minor bleeds that create small, round, dark red spots on the skin called petechiae.

Several petechiae can merge to form bruise-like rashes called purpura.

People with immune thrombocytopenia or ITP may also experience bleeding gums, nose, and blood in the urine or stools. In these cases, platelet counts are typically below 20,000/µl.

Learn more about ITP.

Platelets are a crucial component of the blood. They are responsible for repairing tissue damage and play a vital role in the blood-clotting system, helping stop bleeding and heal wounds. Blood clotting is also known as hemostasis.

The bone marrow produces platelets, and they are present in the blood and spleen.

How do platelets stop bleeding?

If damage occurs to the wall of a blood vessel, the vessel exposes a substance that activates platelets. Activated platelets trigger further events that bring in more platelets and a blood clot forms. This serves to plug any leak.

Activated platelets also release sticky proteins to help form the clot. A protein known as fibrin forms a mesh of threads that holds the plug together.

To diagnose a low platelet count, a doctor may begin by asking some questions and performing a physical examination. The questions might cover symptoms, family history, and medications. The examination will assess for skin rashes and bruising.

A laboratory platelet count will confirm the diagnosis, showing the exact concentration of platelets in the blood. The doctor is likely to perform other blood tests at the same time.

These may include:

  • a complete blood count (CBC)
  • a blood smear test, which involves looking at platelets under a microscope
  • other blood tests to assess blood clotting
  • bone marrow tests

There are two types of bone marrow tests: a bone marrow aspiration and a bone marrow biopsy. In both tests, a doctor uses a needle to take a sample of the bone marrow for examination. Aspiration involves collecting of a small amount of fluid, whereas a biopsy involves collecting some soft tissue.

A doctor may diagnose thrombocytopenia after ruling out other causes of a low platelet count.

Read about treatment for thrombocytopenia.

People with thrombocytopenia can reduce their risk of complications by:

  • taking care to avoid bumps and injuries that might lead to bruises and cuts
  • ensuring that any healthcare professionals who treat them know about this condition, as it can influence treatment decisions
  • taking care with OTC drugs, such as aspirin, acetaminophen, ibuprofen, and naproxen
  • avoiding infections where possible, if a person has undergone a splenectomy

Anyone experiencing unusual symptoms or having other concerns should discuss these with a doctor.

Read about how to increase a platelet count naturally.

Platelets are components of blood cells that play a vital role in forming blood clots. If a person has a low platelet count, called thrombocytopenia, their blood might not clot properly. This can lead to symptoms such as blood loss and bruising.

Causes of a low platelet count include medical conditions and exposure to certain medications and substances, such as alcohol and quinine.

Slightly low platelet counts that do not produce symptoms may not require treatment. However, if symptoms are present, treatment may be necessary.

Treatment can involve switching medications, reducing exposure to certain substances, or treating the underlying medical condition.