A bone marrow biopsy is usually performed from the back of the iliac bone (pelvis). Usually, some liquid marrow is drawn out by a syringe (aspirate), and then a core of bone is taken (trephine) so that the marrow can be examined under the microscope by a haematologist. In suspected ITP, the reason for the biopsy is to make sure that there is no other cause (diagnosis) for low platelets. In most people with ITP a bone marrow biopsy is not needed.