Diagnosis of TMD is typically made through a combination of clinical evaluation and laboratory testing. Key diagnostic steps include: - A complete blood count (CBC) showing elevated white blood cells, particularly blasts. - Peripheral blood smear revealing megakaryoblasts. - Bone marrow biopsy, if necessary, to confirm the presence of megakaryoblasts. - Genetic testing for GATA1 mutations, which are commonly associated with TMD in Down syndrome.