The main tests for thrombocytopenia include routine blood tests, blood smears, and further tests for the cause of the disease, including viral screening, indicators of autoimmune disease, levels of haematopoietic material, and overall assessment of systemic diseases such as thyroid, liver and kidney function. If a haematological disorder is considered a possibility, a bone marrow examination, including a smear of bone marrow aspiration fluid and a bone marrow biopsy, is often required. Some imaging tests such as ultrasound, CT, magnetic resonance imaging (MRI) and PET-CT are also often helpful in determining the cause of thrombocytopenia.