How low does platelet count drop before thrombocytopenia develop?

Thrombocytopenia is generally defined as a platelet count of less than 150,000 platelets per microliter of blood. However, significant clinical symptoms may not appear until the count drops below 100,000 platelets per microliter. In severe cases, platelet counts can fall below 20,000 to 30,000 platelets per microliter, leading to an increased risk of bleeding.