A platelet count is a lab test to measure how many platelets you have in your blood. Platelets are parts of the blood that help the blood clot. They are smaller than red or white blood cells.
How the Test is Performed
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.
The normal number of platelets in the blood is 150,000 to 400,000 platelets per microliter (mcL).
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. If you do not have enough platelets, you may bleed too much.
If your platelet count is below 50,000, your risk of bleeding is much higher. Even every day activities can cause bleeding. If your platelets are low, you need to know how to prevent bleeding and what to do if you are 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
3 of the more common causes of this problem are:
- Cancer treatments, such chemotherapy or radiation
- Drugs and medicines
- Autoimmune disorders, in which the immune system mistakenly attacks and destroys healthy body tissue, such as platelets
HIGH PLATELET COUNT
A high platelet count is 400,000 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
- After certain infections, major surgery or trauma, or allergic reactions
- 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 light-headed
- 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; 2012:chap 26.
Miller JL, Rao AK. Blood platelets and von Willebrand disease. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 40.
Reviewed By: Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.