Thrombocytopenia, how long does it last?

It depends on cause: You need to know the cause. One common cause is called idiopathic thrombocytopenic purpura or itp. This is a chronic condition which can last from a few months to several years. Other causes can be short lived and platelets recover. You should be sure to find out the cause. Or seek a second opinion to learn more about your problem from another specialist.