PLT in a blood test stands for Platelet Count. Platelets, also known as thrombocytes, are tiny blood cells that help the blood to clot. A platelet count test measures the number of platelets in a persons blood. The test is usually part of a complete blood count (CBC) test, which reveals important information about the number of different blood cells in the body. The test is done by taking a blood sample, which is then analyzed using automated laboratory technology. The results are reported as a number of platelets per microliter. A normal platelet count is between 150,000 and 450,000 platelets per microliter of blood. A low platelet count is known as thrombocytopenia, while a high platelet count is known as thrombocytosis. Both high and low platelet counts can have associated risks that can range from not causing any noticeable health problems to being very serious and life-threatening.