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A.D.A.M. Medical Encyclopedia [Internet]. Atlanta (GA): A.D.A.M.; 2013.

A.D.A.M. Medical Encyclopedia.

Platelet count

Thrombocyte count

Last reviewed: February 2, 2013.

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.

Normal Values

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:

Three of the more common causes of this problem are:

  • Cancer treatments such as drugs or chemotherapy, as well as radiation
  • 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
  • Cancer
  • 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

Risks

There is very little risk involved when having your blood taken.

References

  1. Abrams CS. Thrombocytopenia. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 175.
  2. Bain BJ. The peripheral blood smear. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 160.

Review Date: 2/2/2013.

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.

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What works?

  • Platelet transfusions are used to prevent bleeding in patients with low platelet counts due to treatment‐induced bone marrow failurePlatelet transfusions are used to prevent bleeding in patients with low platelet counts due to treatment‐induced bone marrow failure
    This review was undertaken to determine the best use of platelet transfusions for the prevention of bleeding in patients who have haematological disorders and are receiving intensive (myelosuppressive) chemotherapy or stem cell transplantation. The review aimed to look at three main topics. One, what is the evidence to indicate if platelet transfusions should be given to prevent bleeding as compared to a strategy aimed at transfusion when bleeding occurs? Second, if platelet transfusions are given to prevent bleeding, when should they be given, for example, at what level of platelet count when measured in a blood sample? Three, if platelet transfusions are given what platelet dose should be used? We are unable to answer the first question, however new data from two large studies should be available when this review is updated in approximately two years time. With regard to the second question, there is no evidence to suggest a change from the current practice of using a platelet count of 10 x 109/L to trigger the use of platelet transfusions to prevent bleeding. However, more research is required to clarify this issue. The final question can be answered. Using a lower platelet dose did not lead to an increased risk of bleeding and fewer platelets were required. The reduction in the number of platelets used should, theoretically, reduce the risk of adverse events although no true differences were seen in the studies. However, adverse events are uncommon and therefore a statistically significant difference may not be seen.
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