Platelet Tests

Platelets, also known as thrombocytes, are small blood cells. They form in your bone marrow, the sponge-like tissue in your bones. Platelets are essential for blood clotting.

A blood clot is a mass of blood that forms when platelets, proteins, and cells in the blood stick together. When you get hurt, your body forms a blood clot to stop the bleeding. There are two types of platelet tests: a platelet count test and platelet function tests.

A platelet count test measures the number of platelets in your blood: A lower-than-normal platelet count is called thrombocytopenia. This condition can cause you to bleed too much after a cut or other injury that causes bleeding.; A higher-than-normal platelet count is called thrombocytosis. This can make your blood clot more than you need it to.

Blood clots can be dangerous because they can block blood flow.; Platelet function tests check your platelets' ability to form clots. Platelet function tests may include one or more of the following: Closure time. This test measures the time it takes for platelets in a blood sample to plug a small hole in a tiny tube.

It helps screen for different platelet disorders.; Viscoelastometry. This test measures the strength of a blood clot as it forms. A blood clot has to be strong to stop your bleeding.; Platelet aggregometry.

This group of tests is used to measure how well platelets clump together (aggregate).; Lumiaggregometry. This test measures the amount of light produced when certain substances are added to a blood sample. It can help show if there are defects in the platelets.; Flow cytometry.

This test uses lasers to look for proteins on the surface of platelets. It can help diagnose inherited platelet disorders. This specialized test is only available at certain hospitals and laboratories.; Bleeding time.

This test measures how long it takes for bleeding to stop after small cuts are made in your forearm. It was once commonly used to screen for various platelet disorders but is not used much anymore.;

Why this test is done

You may need platelet count and/or platelet function testing if you have symptoms of having lower-than-normal or higher-than-normal platelets.

Symptoms of lower-than-normal platelets include:

• Bleeding for a long time after a minor cut or injury.
• Nosebleeds.
• Unexplained bruising.
• Pinpoint sized red spots on the skin, known as petechiae.
• Purplish, red, or brown spots on your skin, known as purpura. These may be caused by bleeding under the skin.
• Menstrual periods that have a heavy flow or last a long time.
• Blood in your urine, stool (poop), or from your rectum (where stool passes out of your body).

Symptoms of higher-than-normal platelets include:

• Numbness of hands and feet
• Headache
• Dizziness
• Weakness
• Pain, swelling, and warmth in your lower legs

You may also need platelet function testing if you are:

• Having a complicated surgery
• Taking medicines to lower blood clotting

How to prepare

You don't need any special preparations for a platelet count test.

If you are getting a platelet function test, you may need to stop taking certain medicines, such as aspirin and ibuprofen, before your test. Tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.

They will let you know if there are any special instructions to follow.

Sample type

Blood

Other names for this test

platelet count, PLT, PLT count thrombocyte count, platelet function tests, PFT, platelet function assay, PFA, platelet aggregation studies