Health Encyclopedia - Test
A platelet count is a 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
Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.
Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.
Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.
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
You may feel slight pain or a sting when the needle is inserted. You may also feel some throbbing at the site after the blood is drawn.
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 excess bleeding or clotting.
The normal number of platelets in the blood is 150,000 - 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 this bleeding. You need to know how to prevent bleeding and what to do if you have bleeding.
A lower-than-normal platelet count is called thrombocytopenia. Low platelet count can be divided into three major causes:
- Not enough platelets are made in the bone marrow
- Platelets are being destroyed while in the bloodstream
- Platelets are being destroyed while in the spleen or liver
Three of the more common causes of this problem are:
- Cancer treatments such as drugs or chemotherapy, as well as radiation
- Drugs and medicines
- Autoimmune disorders, in which occurs when 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 (thrombocytosis) refers to when your body is making too many platelets
- A type of anemia in which red blood cells in the blood are destroyed earlier than normal.
- After certain infections, major surgery or trauma, allergic reactions
- Certain medicines
- Chronic myelogenous leukemia (CML)
- Polycythemia vera
- 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
There is very little risk involved when having your blood taken.
Abrams CS. Thrombocytopenia. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 175.
Bain BJ. The peripheral blood smear. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 160.
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, Bethanne Black, Stephanie Slon, and Nissi Wang.