A low platelet count is a blood disorder that has a long list of possible causes. It is also known as thrombocytopenia.

Reduced platelet content in the blood is not always a serious problem. However, the condition affects the ability of the blood to clot, and wounds can bleed severely with this condition. This can have serious complications in some cases.

This article examines the conditions, medications, and substances that can cause a low platelet count, including idiopathic thrombocytopenic purpura (ITP), as well as how to recognize symptoms and what to expect from treatment.

The level of platelets is usually low as a result of two main factors.

Either an underlying medical condition is causing the reduced level, or an individual is taking a medication or substance that serves to reduce platelet count.

Medication and substances

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Platelets are the component in blood that enables it to clot.

Medicines, poisonous substances, heavy alcohol drinking, and even drinks with quinine in them, such as tonic water, can cause low platelet counts. Quinine is also found in tablets for leg cramps.

If a doctor finds one of these substances to be the cause of a low platelet count, stopping intake of the substance can return the platelet count to normal. If the cause is a drug being taken for a different condition, the prescribing doctor might change the medication.

Poisons that can cause thrombocytopenia include pesticides, arsenic, and benzene.

The following are antiplatelet or anti-clotting drugs that reduce the platelet count:

  • glycoprotein IIb/IIIa inhibitors, including abciximab, eptifibatide, and tirofiban
  • heparin

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

  • acetaminophen
  • ibuprofen
  • naproxen

Some prescribed medications can also cause thrombocytopenia, including:

  • amiodarone
  • ampicillin and other antibiotics
  • cimetidine
  • piperacillin
  • seizure medications, such as carbamazepine
  • sulfonamides, such as trimethoprim-sulfamethoxazole
  • vancomycin

Low platelet counts have a range of medical causes. The main causes are either reduced production or increased breakdown of platelets.

Platelets can also become trapped in greater numbers by the spleen. A number of conditions can lead to enlargement of this abdominal organ, which is the result of a number of conditions.

Causes that affect the production of platelets in the bone marrow include:

  • leukemia and other cancers that can replace the bone marrow
  • certain types of anemia
  • infections with viruses, including HIV and hepatitis C
  • sepsis
  • acute respiratory distress syndrome (ARDS)
  • cancer treatments, such as radiation and chemotherapy
  • autoimmune diseases, such as ITP
  • some medications, such as antibiotics, cardiovascular drugs, and seizure medications
  • exposure to toxic substances
  • excessive alcohol consumption
  • a family history of low platelet levels

A small proportion of pregnancies destroy platelets as they near completion. This condition is usually mild enough not to need treatment and returns to normal in time.

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People with a low platelet count may bruise more easily.

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

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

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

ITP can also cause the gums or nose to bleed without reason and the presence of blood in the urine or stools. In these cases of ITP, platelet counts are below 20,000 per μl.

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

Platelets are not invisible to the naked eye. The bone marrow produces them, and they travel in the blood for an average of 10 days before being destroyed.

How do platelets stop bleeding?

Platelets plug a leak in a blood vessel wall if it becomes broken or injured.

When a blood vessel wall is damaged, it exposes a substance that activates platelets. Activated platelets trigger further events that bring in more platelets, and a blood clot starts to form. 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.

A platelet count measures the concentration of platelets in the blood. A technician would carry this test out in a laboratory.

A normal platelet count is around 140,000 to 450,000 platelets per microliter (μl) of blood. When the number of platelets is low, this concentration reduces.

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

The risk of bleeding increases as the platelet count drops, but bleeding problems are unlikely unless the count is less than 80,000-100,000 platelets per μl.

The following platelet counts carry the risk of serious bleeding:

  • Between 20,000 and 50,000 per μl: There is more risk of bleeding when injured.
  • Less than 20,000 per μl: Bleeding happens even without injury.
  • Below 10,000 platelets per μl: Spontaneous bleeding can be severe and a risk to life.

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Blood tests can help identify a low platelet count.

A doctor will ask some questions and perform 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 bone marrow test
  • a complete blood count (CBC)
  • a blood smear test, which looks at platelets under a microscope
  • other blood tests to assess blood clotting

Some people may need to give a sample of their bone marrow. This involves taking fluid from the marrow through a needle. This is called a bone marrow biopsy.

A diagnosis of ITP may be made after ruling out other causes of low platelet count.

Slightly low platelet counts that do not produce symptoms may not require treatment.

For platelet counts low enough to cause physical effects, a doctor will address the cause directly. There is a wide range of possible causes. Treatment could involve switching medication or attempting to resolve an underlying medical condition.

For cases of ITP, treatment may include drugs that suppress the immune system, such as a corticosteroid drug called prednisone.

In severe cases, a blood transfusion may be necessary.

If there are no increases in platelet count after a year, a surgeon may remove the spleen in a procedure called a splenectomy. People with extremely severe or emergency presentations of low platelet count can be treated with a transfusion of platelets.

People who have a diagnosis of this condition can reduce the risk of complications by:

  • taking care to avoid bumps and injuries that might lead to bruises and cuts
  • ensuring that all of their health workers know about this condition, as it can impact treatment decisions
  • taking care with over-the-counter (OTC) drugs, as many contain aspirin
  • avoiding infections where possible, in the case of people who have had their spleen removed

Any concerns or unusual symptoms should be reported to a doctor.

ITP refers to idiopathic thrombocytopenic purpura. It is also known as immune thrombocytopenia.

The name of the condition relates to bleeding-induced rashes that occur as a result of a low platelet count. Idiopathic means that the cause is not known.

In ITP, the immune system attacks platelets. This often follows an infection in children.

ITP is a rare condition. The internal clotting that occurs can use up a large number of platelets.