platelets are the tiny blood cells that help stop bleeding by binding together to form a clump or plug at sites of injury inside blood vessels. a normal platelet count is between 150 000 and 450 000 platelets per microliter (one-millionth of a liter abbreviated mcl). the average platelet count is 237 000 per mcl in men and 266 000 per mcl in women. a platelet count below 150 000 per mcl is called thrombocytopenia while a platelet count over 450 000 is called thrombocytosis. platelets seem to have a large backup capacity: blood typically still clots normally as long as the platelet count is above 50 000 per mcl (assuming no other problems are present). spontaneous bleeding doesn’t usually occur unless the platelet count falls to 10 000 or 20 000 per mcl. platelets are constantly being produced in the bone marrow. a low or high platelet count is not often a problem by itself but can frequently be a sign of another medical condition. for this reason high or low platelet counts require additional medical attention. 329
what is a normal platelet count?