If for any reason your blood platelet count falls below normal, the condition is called
thrombocytopenia. Normally, you have anywhere from 150,000 to 450,000 platelets per microliter of circulating blood. Because each platelet lives only about 10 days, your body continually renews your platelet supply by producing new platelets in your bone marrow.
Thrombocytopenia has many possible causes.