I. Introduction

Thrombocytopenia develops for several reasons, including genetic disorders, cancer, and the use of certain medications. Essential thrombocythemia, also known as primary thrombocythemia, occurs when the bone marrow makes too many platelets. Researchers do not know what causes this condition. Essential thrombocythemia is rare, affecting just 1 to 24 individuals out of every one million people in the world. Secondary thrombocytosis occurs as a result of another illness. For example, secondary thrombocytosis is often caused by infection, cancer, or anemia.

This guide offers a detailed overview of platelet count testing, including why it’s done, the type of sample required, and answers to frequently asked questions. It also explains the causes, symptoms, and treatment options for thrombocytopenia and thrombocythemia/thrombocytosis.

II. Overview of the Platelet Count

Why should I get tested?

The purpose of the platelet count is to determine if a person has a normal or an abnormal number of platelets in the blood. Anyone with signs of a high platelet count or low platelet count should have the test. Chest pain and weakness are some of the signs associated with too many platelets, while easy bruising, bleeding gums, and frequent nosebleeds are among the signs associated with a lack of platelets. The platelet count may also be performed as part of a routine physical, especially in older people.

When should I get tested?

The platelet count should be performed at the following times:

  • When an individual has unexplained bleeding or bruising
  • During a complete blood count, a test that counts the platelets, white blood cells, and red blood cells in a person’s blood
  • Within five to 10 days of starting heparin or another medication that prevents blood clots
  • After starting chemotherapy, which can deplete platelets and other cell types
  • As part of a routine physical, if the ordering provider determines it is necessary

What is required for the test?

A platelet count can be performed on a small sample of blood.

How do I prepare for the test?

No special preparation is required for the platelet count, and it is often ordered with other tests. Some of these tests may require fasting or another type of preparation. It’s important to ask if any special preparation is required before having blood drawn.

III. The Basics of Thrombocytopenia, Essential Thrombocythemia, and Secondary Thrombocytosis


Thrombocytopenia is characterized by an abnormally low number of platelets in an individual’s blood. The condition typically develops when a person’s bone marrow does not make the right number of platelets, when the spleen stores too many platelets instead of allowing them to circulate in the bloodstream, or when the body destroys or uses platelets faster than normal. Each of these issues has several potential causes.

Cancer is a common reason why the bone marrow does not make the right number of platelets, as cancer cells can damage the bone marrow. Some of the treatments for cancer, such as radiation therapy, destroy the bone marrow, leaving it unable to produce an adequate number of platelets. A condition called aplastic anemia can also result in a low platelet count. Aplastic anemia causes the bone marrow to stop manufacturing blood cells, leaving an individual without the platelets needed to prevent bleeding. Alcohol use, viruses, some medications, and exposure to harmful chemicals can also cause the bone marrow to stop producing enough platelets.

In individuals whose spleen stores too many platelets, the spleen is usually enlarged, a condition known as splenomegaly. This condition often develops in people who have cancer or cirrhosis, a condition that causes liver damage. Several conditions can cause the body to destroy platelets or use them faster than normal. Surgery, pregnancy, and widespread infection are all associated with platelet destruction. The body also destroys platelets when exposed to certain medications, such as sulfa antibiotics and medications used to control seizures.

Thrombocytopenia may not cause any symptoms at first. Once the platelet count becomes abnormally low, however, the individual may notice unexplained bruises or bleeding of the gums. Some people also experience nosebleeds or develop a rash made up of tiny points of redness. A severely low platelet count may lead to spontaneous bleeding, which becomes a medical emergency.


Essential Thrombocythemia

Essential thrombocythemia is a genetic disorder associated with mutations in the CALR, JAK2, TET2, THPO, or MPL genes. JAK2 and CALR mutations are the most common. The JAK2 gene contains instructions for manufacturing the proteins involved in cell proliferation, which is the growth and division of cells. CALR also plays a role in protein manufacturing; the gene contains instructions for producing a protein that tells other proteins how to fold correctly. A mutation in either of these genes can cause the bone marrow to produce too many platelets.

The most common sign of essential thrombocythemia is abnormal blood clotting. When blood clots form, they can cause strokes by blocking the flow of blood to the brain. Blood clots in the legs can cause ongoing pain and swelling. If a clot dislodges and travels to the lungs, it can cause difficulty breathing, placing the individual’s life at risk. Although people with essential thrombocythemia have too many platelets, they may also experience abnormal bleeding, which is thought to be caused by a reduction in the amount of protein available to help the blood clot normally. Abnormal bleeding can take the form of bleeding gums, frequent nosebleeds, or even bleeding in the gastrointestinal system. Essential thrombocythemia may also cause headaches, general weakness, an enlarged spleen, and burning or tingling of the skin.

Secondary Thrombocytosis

Secondary thrombocytosis develops when an underlying medical condition causes too many platelets to accumulate in the bloodstream. Surgical procedures can cause this condition, especially when they involve the spleen, as the spleen is responsible for storing some of the platelets in the body. Cancer, infections, iron-deficiency anemia, and widespread inflammation are some of the other common causes of secondary thrombocytosis.

Like essential thrombocythemia, secondary thrombocytosis can cause blood clots to form, increasing the risk for stroke and heart attack. Some people with this condition develop blood clots in the abdomen. Individuals with secondary thrombocytosis are also at risk for developing bleeding problems, although these problems are rarely life-threatening. Unlike essential thrombocythemia, secondary thrombocytosis goes away when the underlying condition is treated. For example, in someone with iron-deficiency anemia, secondary thrombocytosis is likely to resolve once the individual starts taking iron supplements and the deficiency has been reversed.

IV. How a Platelet Count Works

During a platelet count, a laboratory scientist counts the number of platelets in a blood sample to determine if there are too many, too few, or just the right amount. A manual count is performed by diluting a blood sample with a solution of 1% ammonium oxalate. The ammonium oxalate causes any mature red blood cells in the sample to disintegrate, leaving the platelets, white blood cells, and immature red blood cells intact. The laboratory scientist then uses a device called a hemocytometer to isolate the platelets in a specific chamber. Once the platelets have been isolated, they are counted per microliter of blood.

The platelet count requires a blood sample, which is obtained via a procedure known as a venipuncture. During this procedure, a phlebotomist or medical assistant verifies the patient’s name and date of birth, identifies an appropriate venipuncture site, and performs several tasks to ensure the individual’s safety and comfort. Before inserting a needle into the vein, the phlebotomist typically ties a tourniquet around the upper arm, which makes the vein easier to see and feel. To prevent infection, the phlebotomist cleans the skin with a wipe containing alcohol or another antiseptic substance. Finally, a needle is inserted into the vein, and blood is directed into a collection tube.

V. Treatment for Thrombocytopenia, Essential Thrombocythemia, and Secondary Thrombocytosis


A mild decrease in an individual’s platelet count may not require any treatment, as the remaining platelets still have the ability to help the blood clot normally. If an individual’s platelet count drops severely, however, treatment may be necessary to prevent excessive bleeding. In some cases, individuals with thrombocytopenia take steroids to slow the rate of platelet destruction. Medications to suppress the immune response may be given when platelet destruction is caused by an autoimmune disorder or other problems with the immune system.

In individuals with a high risk of bleeding, or those who have already started bleeding due to thrombocytopenia, it may be necessary to administer healthy platelets via a platelet or blood transfusion.

Essential Thrombocythemia

Some people with essential thrombocythemia do not have any symptoms, so they don’t require treatment. Individuals with symptoms that are clearly a result of an elevated platelet count have several treatment options. No single treatment plan is right for everyone with this condition, so it’s important for anyone with essential thrombocythemia to be monitored by a medical professional. In some people with this condition, low-dose aspirin can be taken daily to prevent blood clots. Interferon, hydroxyurea, and anagrelide are also used to treat essential thrombocythemia.

Interferon reduces an individual’s platelet count by inhibiting the growth of progenitors called megakaryocytes. A megakaryocyte is a large cell produced by the bone marrow, and this large cell eventually breaks into platelets. Hydroxyurea is used to treat cancer; one of its side effects is a reduced platelet count, so it’s sometimes used to treat essential thrombocythemia. People who can’t tolerate hydroxyurea may be prescribed anagrelide, which is used to reduce an individual’s platelet count.

Secondary Thrombocytosis

In people with secondary thrombocytosis, treatment is aimed at resolving the underlying cause of the elevated platelet count. Once the underlying cause is resolved, the individual’s platelet count should return to normal.


What is a normal platelet count?

A normal platelet count ranges from 150,000 to 400,000 platelets per microliter of blood.

Why are platelets so important?

When someone sustains an injury, platelets help the blood clot, preventing excessive blood loss. Without enough platelets, it’s possible for someone to bleed so excessively that hypovolemic shock develops. Hypovolemic shock is a life-threatening condition that makes it difficult for the heart to pump blood to all of the body’s organs and tissues. If hypovolemic shock is not treated promptly, it can lead to organ failure.

How long does it take to learn the results of a platelet count?

The results of a platelet count are usually available to the ordering physician within 24 hours; however, it may take two to three days for the provider to review the result and share the information with the patient.

Are there any risks to having a platelet count performed?

The risks of the platelet count are the same as the risks for any other blood test. Venipuncture may cause bruising or bleeding at the needle insertion site. In some people, having blood drawn may lead to sweating, fainting, or a drop in blood pressure. There is also a slight risk of infection if the skin is not cleansed properly before the needle is inserted.

What can affect the results of a platelet count?

Some environmental factors and lifestyle habits can affect an individual’s platelet count. For example, people living at a high altitude may have higher platelet counts than people residing at lower altitudes. Exercising vigorously before a blood draw can also cause an individual’s platelet count to be elevated.

Which other tests may be required if a platelet count reveals an abnormal number of platelets in the blood?

If an individual has too many platelets without any obvious underlying cause, the ordering provider may request genetic testing to determine if the individual has any of the genetic mutations associated with essential thrombocythemia. For an individual with thrombocytopenia, the provider may order a blood smear to determine if the platelets are abnormal in shape or size.

VII. Additional Resources

To learn more about thrombocytopenia, essential thrombocythemia, and secondary thrombocytosis, and for more information about testing for these conditions, use the following resources.

Name Website Summary
The Mayo Clinic www.mayoclinic.org The Mayo Clinic provides an overview of thrombocytopenia, including causes, symptoms, and potential complications.
Genetics Home Reference www.ghr.nlm.nih.gov Genetics Home Reference explains the gene mutations associated with essential thrombocythemia.
Merck Manuals www.merckmanuals.com The consumer version of the Merck Manuals provides a plain-language overview of secondary thrombocytosis.
MedlinePlus www.medlineplus.gov Learn more about the complete blood count, which includes a platelet count, white blood cell count, and red blood cell count.
The Hemophilia, von Willebrand Disease & Platelet Disorders Handbook www.hog.org The nonprofit organization Hemophilia of Georgia outlines some of the tests available to aid in the diagnosis and management of platelet disorders.

VIII. Learn More From Our Sources