The platelet count test is a common medical test that measures the number of platelets in a person’s blood. Platelets are small, colorless blood cells that help with blood clotting and prevent excessive bleeding. The test is usually done as part of a complete blood count (CBC), which is a routine blood test that is performed to evaluate a person’s overall health. The platelet count test is used to diagnose and monitor various medical conditions, such as bleeding disorders, thrombocytopenia (low platelet count), and thrombocytosis (high platelet count). The results of the platelet count test are usually reported in the number of platelets per microliter of blood, and the normal range is typically between 150,000 and 450,000 platelets per microliter.