Platelet Count


A platelet count is a lab test to measure how many platelets you have in your blood. Platelets are parts of the blood that helps the blood clot. They are smaller than red or white blood cells.

Alternative Names

Thrombocyte count

How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

Most of the time you do not need to take special steps before this test.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.

Why the Test is Performed

The number of platelets in your blood can be affected by many diseases. Platelets may be counted to monitor or diagnose diseases, or to look for the cause of too much bleeding or clotting.

Normal Results

The normal number of platelets in the blood is 150,000 to 400,000 platelets per microliter (mcL) or 150 to 400 × 109/L.

Normal value ranges may vary slightly. Some lab use different measurements or may test different specimens. Talk to your doctor about your test results.

What Abnormal Results Mean


A low platelet count is below 150,000 (150 × 109/L). If your platelet count is below 50,000 (50 × 109/L), your risk of bleeding is high. Even every day activities can cause bleeding.

A lower-than-normal platelet count is called thrombocytopenia. Low platelet count can be divided into 3 main causes:

  • Not enough platelets are being made in the bone marrow
  • Platelets are being destroyed in the bloodstream
  • Platelets are being destroyed in the spleen or liver

Three of the more common causes of this problem are:

  • Cancer treatments, such as chemotherapy or radiation
  • Drugs and medicines
  • Autoimmune disorders, in which the immune system mistakenly attacks and destroys healthy body tissue, such as platelets

If your platelets are low, talk to your health care provider about how to prevent bleeding and what to do if you are bleeding.


A high platelet count is 400,000 (400 × 109/L) or above

A higher-than-normal number of platelets is called thrombocytosis. It means your body is making too many platelets. Causes may include:

  • A type of anemia in which red blood cells in the blood are destroyed earlier than normal (hemolytic anemia)
  • Anemia due to low iron, sickle cell disease
  • After certain infections, major surgery or trauma
  • Cancer
  • Certain medicines
  • Bone marrow disease called polycythemia vera
  • Bone marrow making too many platelets without a known cause (primary thrombocythemia)
  • Recent spleen removal

Some people with high platelet counts may be at risk of forming blood clots. Blood clots can lead to serious medical problems


Veins and arteries vary in size so it may be harder to take a blood sample from one person than another.

Other slight risks from having blood drawn may include:

  • Excessive bleeding
  • Fainting or feeling lightheaded
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)


Cantor AB. Thrombocytopoiesis. In: Hoffman R, Benz EJ Jr, Silberstein LE, Heslop HE, Weitz JI, Anastasi J, eds. Hematology: Basic Principles and Practice. 6th ed. Philadelphia, PA: Elsevier Saunders; 2013:chap 26.

Chernecky CC, Berger BJ. Platelet (thrombocyte) count - blood. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:886-887.

Review Date: 2/7/2017

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Information developed by A.D.A.M., Inc. regarding tests and test results may not directly correspond with information provided by UCSF Medical Center. Please discuss with your doctor any questions or concerns you may have.