Platelets are tiny blood cells that help your body form clots to stop bleeding. If one of your blood vessels gets damaged, it sends out signals that are picked up by platelets. The platelets then rush to the site of damage and form a plug, or clot, to repair the damage.our health care provider may do a blood test called a complete blood count to find out if your bone marrow is making the right number of platelets: A normal platelet count is 150,000 to 450,000 platelets per microliter of blood. Risk for bleeding develops if a platelet count falls below 10,000 to 20,000.