Platelet count

Definition

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

LOW PLATELET COUNT

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.

HIGH PLATELET COUNT

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)
• Iron deficiency
• After certain infections, major surgery or trauma
• Cancer
• Certain medicines
• Bone marrow disease called myeloproliferative neoplasm (which includes polycythemia vera)
• Spleen removal

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

Risks

There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another, and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

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

References

Cantor AB. Thrombocytopoiesis. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 7th ed. Philadelphia, PA: Elsevier; 2018:chap 28.

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.