Platelet count |
| Definition: |
| A test that measures the number of platelets in blood. Platelets are necessary for normal blood clotting (hemostasis). Most importantly, they aggregate (clump) together to plug small holes in damaged vessels. They also activate factor VIII (a component of the coagulation cascade) and release phospholipids necessary for the coagulation cascade. |
| Alternative Names: |
| Thrombocyte count |
| How the test is performed: |
| Adult or child: Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding. Infant or young child: The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding. |
| How to prepare for the test: |
| Adults: No special preparation is necessary. Infants and children: The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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| How the test will feel: |
| When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing. |
| Why the test is performed: |
| The platelet count can be affected by many disease states. It may also be measured to assess the cause of excess bleeding. |
| Normal Values: |
| 150,000 to 400,000/mm3 Note: mm3 = millimeters cubed |
| What abnormal results mean: |
| A diminished number of platelets (below the lower limit of normal) is called thrombocytopenia and an elevated number (above the upper limit of normal) is called thrombocytosis. A decreased numbers of platelets may be associated with:
This test may be performed under many conditions and in the assessment of many disease states. |
| What the risks are: |
| Special considerations: |
| Drugs that can decrease platelet counts include chemotherapeutic agents, chloramphenicol, colchicine, H2 blocking agents, heparin, hydralazine, indomethacin, isoniazid, quinidine, streptomycin, sulfonamide, thiazide diuretic, and tolbutamide. Veins and arteries vary in size from one patient 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. |
Reviewed By: Rebecca Elstrom, M.D., Division of Hematology-Oncology, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.
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